BACKGROUND

1. Field of the Invention: The present invention generally relates to processes for the synthesis of drospirenone.

2. Description of the Relevant Art: Drospirenone is a synthetic steroid with progestin, anti- mineral corticoid and anti androgen activity. Drospirenone is currently being used as a synthetic progestin in oral contraceptive formulations. A regioselective synthesis for drospirenone has been described (see e.g., Angew. Chem. 94, 1982, 718) that uses the 17 keto derivative (V) as a key intermediate.

The synthesis of intermediate (V) and the transformation of intermediate (V) into drospirenone has been described in, for example, U.S. Published Patent Application Nos.: 2009/0023914; 20080207575; 2008/0200668; 2008/0076915, 20070049747, and 20050192450; U.S. Patent Nos. 6,933,395; 6,121,465, and 4,129,564, European Patent No. 0 075 189 and PCT Publication No. WO 2006/061309, all of which are incorporated herein by reference. Many of these routes introduce the required C3 side chain in the 17 position of intermediate (V). These conversions are usually carried out with carbanions, such as propargylalcohol, trimethylsulfoxonium iodide, or the use of the anion generated from a suitably protected derivative of 1- bromopropionaldehyde. After oxidation of the 3-hydroxy substituent to a 3-keto group, and the oxidative formation of the 17-spirolactone, the 3-keto-5-hydroxy~17-spirolactone is transformed via acid catalysis into drospireneone. If the oxidation is performed under acidic conditions at elevated temperatures, the oxidation and elimination can be run without isolation of the intermediate products.

Most of these procedures rely on the acid-catalyzed elimination of the 5-hydroxy group in the last step of the synthesis. It has been documented that 15,16-methylene-17-spirolactones are prone to undergo rearrangement to generate the inverted 17-spirolactone under mild acidic conditions (see, for example, Tetrahedron Letters, Vol. 27, No 45, 5463-5466) in considerable amounts. This isomer has very similar physical chemical properties, and typically requires chromatographic separation or repeated fractional recrystallizations to purify the product. This isomerization can make these approaches less desirable from an economical point of view.

For the above given arguments, a process that avoids the acidic treatment of intermediates containing the 15, 16-methylene- 17-spirolactone could offer a significant advantage because of the avoidance of the generation of the undesired 17-spirolactone isomer.

SUMMARY

Pn one embodiment, a method of making drospirenone includes: reacting the intermediate (1) with a propargyl alcohol anion, as depicted in the reaction (I) to yield intermediate (2), where each R ¹ , R ² is independently H, Si(R ⁵ ) ₃ , C(R ⁶ ) ₂ (OR ⁵ ) or CR ⁶ (OR ⁵ ) ₂ ; Z is CH ₂ OR ³ , CN, or CO ₂ R ⁴ ; where each R ³ is independently alkyl, Si(R ⁵ ) ₃ , or CH(OR ⁵ ) ₂ , phenyl, or benzyl; each R ⁴ and R ⁵ is independently hydrogen, alkyl, phenyl, benzyl, or an alkali metal and each R ⁶ is independently alkyl or hydrogen;

(!) reducing the alkyne functionality of intermediate (2) to form intermediate (3), as depicted in reaction (II);

(H)

oxidizing intermediate (3) to form intermediate (4), as depicted in reaction (III);

(IH)

treating intermediate (4) with a base to produce intermediate (5), as depicted in reaction (IV); and

(ivi converting the intermediate (5) to drospirenone by forming the spirolactone substituted, as depicted in reaction (V).

5 Drospirenone (V)

In an embodiment, R ¹ and R ² are H; Z is CH ₂ OR ³ ; and R ³ is Si(R ⁵ ) ₃ . hi reaction (I) the propargyl alcohol anion may be generated by the reaction of HC≡CCH ₂ OR ³ with potassium t- butoxide, wherein R ³ is tert-butyldimethyl silyl. Reaction (III) maybe performed using a chromium based oxidation. The elimination reaction (IV) may be performed using an alkali metal alkyloxide. The conversion of intermediate (5) to drospirenone is performed using a chromium based oxidation.

In an embodiment, R ¹ and R ² are H; Z is CH ₂ CO ₂ R ⁴ ; and R ⁴ is alkyl. hi reaction (I) the propargyl alcohol anion may be generated by the reaction of HC=CCH ₂ CO ₂ R with lithium hexamethyldisilylamide. The oxidation reaction (III) may be performed using 2,2,6,6- tetramethylpiperidine-1-oxyl or a derivative thereof. The elimination reaction (IV) may be performed using an alcoholic alkali hydroxide. The conversion of intermediate (5) to drospirenone may be performed under acidic conditions (e.g., using an organic acid), hi either embodiment, reaction (II) may be performed using Pd in the presence of hydrogen.

Li an alternate embodiment, a method of making drospirenone comprising: reacting the intermediate (1) with a propargyl alcohol, as depicted in the reaction (V) to yield intermediate (2), where each R ¹ , R ² is independently H, Si(R ⁵ ) ₃ , C(R ⁶ ) ₂ (OR ⁵ ) or CR ⁶ (OR ⁵ ) ₂ ;

Z is CN or CO ₂ R ⁴ ; where each R ³ is independently alkyl, Si(R ⁵ ) ₃ , or CH(OR ⁵ ) ₂ , phenyl, or benzyl; each R ⁴ and R ⁵ is independently hydrogen, alkyl, phenyl, benzyl, or an alkali metal and each R ⁶ is independently alkyl or hydrogen;

oxidizing intermediate (2) to form intermediate (9), as depicted in reaction (VI);

(YJ)

converting the intermediate (9) to drospirenone as depicted in reaction (VII).

9 Drospirenone (VII)

In an embodiment, R and R ² are H; Z is CH ₂ CO ₂ R ⁴ ; and R ⁴ is alkyl. In reaction (V) the propargyl alcohol anion may be generated by the reaction of HC≡CCH ₂ CO ₂ R with lithium hexamethyldisilylamide. The oxidation of reaction (VI) may be performed using 2,2,6,6- tetramethylpiperidine-1-oxyl or a derivative thereof. The conversion of intermediate (9) to drospirenone, in one embodiment, includes: reducing the alkyne functionality of intermediate (9) to form intermediate (8), as depicted in reaction (VIII); and

9 2 (vπi) treating intermediate (8) with an aqueous base followed by an aqueous acid to form drospirenone.

Pn an embodiment, reaction (VIII) is performed using Pd in the presence of hydrogen. The conversion of intermediate (9) to drospirenone, in an embodiment, includes: treating intermediate (9) with an aqueous acid to produce intermediate (10), as depicted in reaction (IX); and

10 (IX)

reducing the alkyne functionality of intermediate (10) to form intermediate QT) ₅ as depicted in reaction (X); and

10 11 (X)

treating intermediate QLL) with an aqueous base followed by an aqueous acid to form drospirenone.

Reaction (X) is performed using a metal catalyst, including, but not limited to, Rh, Raney Nickel, Ir, and Pd in the presence of hydrogen.

In an alternate embodiment, a method of making drospirenone includes: reacting the intermediate (V) with a methylene ylide, as depicted in the reaction (XI) to yield intermediate (12), where each R ¹ , R ² is independently H, Si(R ⁵ ) ₃ , C(R ⁶ ) ₂ (OR ⁵ ) or CR ⁶ (OR ⁵ ) ₂ ; Z is CH ₂ OR ³ , CN, or CO ₂ R ⁴ ; where each R ³ is independently alkyl, Si(R ⁵ ) ₃ , or CH(OR ⁵ ) ₂ , phenyl, or benzyl; each R ⁴ and R ⁵ is independently hydrogen, alkyl, phenyl, benzyl, or an alkali metal and each R ⁶ is independently alkyl or hydrogen;

reacting the intermediate (12) with a carbanion as depicted in the reaction (XII) to yield intermediate (13),

12 13 (XH)

oxidizing intermediate (13) to form intermediate (14), as depicted in reaction

13 14 (XIH)

converting the intermediate (14) to drospirenone as depicted in reaction (XIV).

14 Drospirenone

In an embodiment, the methylene ylide is a sulfur ylide. In an embodiment, Z is CN, and R ¹ and R ² are C(R ⁶ ^(OR ⁵ ). The oxidation of reaction (XIII) is performed using a chromium based oxidation. The conversion of intermediate (14) to drospirenone may be performed by treating intermediate (14) with an aqueous base followed by an aqueous acid to form drospirenone.

In an embodiment, drospirenone may be synthesized from any compound having the structure 15:

15

where Z is CN or CO ₂ R ⁴ ; R ⁷ is -OR ¹ or =0; R ⁸ is H and R ⁹ is -OR ² or R ¹ and R ² together form a double bond; R ¹⁰ , R ¹¹ , R ¹² , and R ¹³ are H or R ¹⁰ , R ¹¹ , R ¹² , and R ¹³ together form a triple bond; where each R ¹ and R ² is independently H, Si(R ⁵ ) ₃ , C(R ⁶ ) ₂ (OR ⁵ ) or CR ⁶ (OR ⁵ ) ₂ ; where each R ⁴ and R ⁵ is independently hydrogen, alkyl, phenyl, benzyl, or an alkali metal; and each R ⁶ is independently alkyl or hydrogen, hi an embodiment, drospirenone may be synthesized from any compound having the structure 16:

16

where Z is CN or CO ₂ R ⁴ R ⁷ is -OR ¹ or =0;

R is H and R is -OR or R and R together form a double bond; where each R ¹ and R ² is independently H, Si(R ⁵ ) ₃ , C(R ⁶ ) ₂ (OR ⁵ ) or CR ⁶ (OR ⁵ ) ₂ ; where each R ⁴ and R ⁵ is independently hydrogen, alkyl, phenyl, benzyl, or an alkali metal; and each R ⁶ is independently alkyl or hydrogen.

In an embodiment, drospirenone may be synthesized from any compound having the structure 17:

17

where Z is CN or CO ₂ R ⁴ ; R ⁷ Is -OR ¹ Or =O;

R ⁸ is H and R ⁹ is -OR ² or R ¹ and R ² together form a double bond; where each R ¹ and R ² is independently H, Si(R ⁵ ) ₃ , C(R ⁶ ) ₂ (OR ⁵ ) or CR ⁶ (OR ⁵ ) ₂ ; where each R ⁴ and R ⁵ is independently hydrogen, alkyl, phenyl, benzyl, or an alkali metal; and each R ⁶ is independently alkyl or hydrogen. In an embodiment, drospirenone may be synthesized from any compound having the structure 18:

18

where Z is CN or CO ₂ R ⁴ ; and where R ⁴ is hydrogen, alkyl, phenyl, benzyl, or an alkali metal. In an embodiment, drospirenone may be synthesized from any compound having the structure 19;

19

where Z is CN or CO ₂ R ; and where R ⁴ is hydrogen, alkyl, phenyl, benzyl, or an alkali metal.

In an embodiment, drospirenone may be synthesized from any compound having the structure 20:

20

where Z is CN or CO ₂ R ⁴ ; and where R ⁴ is hydrogen, alkyl, phenyl, benzyl, or an alkali metal. In an embodiment, drospirenone may be synthesized from any compound having the structure 21:

21 where Z is CN or CO ₂ R ⁴ ; and where R ⁴ is hydrogen, alkyl, phenyl, benzyl, or an alkali metal.

In an embodiment, drospirenone may be synthesized from any compound having the structure 22:

22

where Z is CN or CO ₂ R ⁴ ; and where R ⁴ is hydrogen, alkyl, phenyl, benzyl, or an alkali metal.

In an embodiment, drospirenone may be synthesized from any compound having the structure 23:

23

where Z is CN or CO ₂ R ⁴ ; and where R ⁴ is hydrogen, alkyl, phenyl, benzyl, or an alkali metal.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention will become apparent to those skilled in the art with the benefit— of— the —following detailed -description- of- embodiments -and- upon- reference _ -to_ the _ accompanying drawings in which: FIGS. 1-5 depict alternate reaction schemes for the synthesis of drospirenone.

While the invention may be susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. The drawings may not be to scale. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but to the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

hi one embodiment, drospirenone may be synthesized according to the scheme depicted in FIG. 1. FIG. 1 depicts a propargyl alcohol anion addition to the 17-keto substituent of the intermediate (1). R ¹ and R ² of intermediate (1) may be H, Si(R ⁵ ) ₃ , C(R ⁶ ) ₂ (OR ⁵ ) or CR ⁶ (OR ⁵ ) ₂ where each R ⁵ is independently alkyl, phenyl, or benzyl, and each R ⁶ is independently alkyl or hydrogen. The propargyl alcohol anion has the structure: ^" C≡CCH ₂ OR ³ ; where R ³ is independently alkyl, Si(R ⁵ ) ₃ , or CH(OR ⁵ ) ₂ , phenyl, or benzyl; and each R ⁵ is independently alkyl, phenyl, or benzyl. A lithium or potassium anion of the propargyl alcohol may be generated in situ using know methods as described in U.S. Published Patent Application Nos.: 2009/0023914; 20080207575; and 20050192450; and U.S. Patent Nos. 6,933,395 and 6,121,465, all of which are incorporated herein by reference. Reaction of the propargyl alcohol anion with intermediate (V) generates the 17- hydroxy addition product (2).

The 17-hydroxy addition product (2) may be hydrogenated in the presence of a suitable catalyst (e.g., Pd, Pt, Rh, Ru, Ir, Ni, and Raney Nickel) in the presence of hydrogen to give the saturated intermediate (3). Examples of suitable catalysts include, but are not limited to Pd/C and rhodium phosphine catalysts.

The resulting hydrogenated intermediate (3) may be treated with an oxidant to oxidize the 3-hydroxy substituent without effecting formation of the 17-spirolactone. Suitable oxidants include, but are not limited to chromium based oxidants (CrO ₃ /pyridine, Jones reagent, pyridiniumdichroffiate ^~ (PDC), ^" l)yri^iniunr ^" cKlofδchfonTate ^" (PCC), ^~ etc.)7 ^" IBX7 ^" KMnO ₄ rMnO ₂ , ^~ Ruθ4 ^~ an ^" d ^" 2,2,6,6-Tetramethylpiperidine-l-oxyl (TEMPO) or derivatives of TEMPO (e.g., 4-hydroxy- TEMPO, 4-acetamido-TEMPO, 4-methoxy-TEMPO, 4-benzyl-TEMPO, and polymer-supported TEMPO). Further details regarding TEMPO oxidations of steroidal compounds is described in U.S. Patent No. 2007/0049747 to Seilz et al., which is incorporated herein by reference. . Oxidation of the 3-hydroxy substituent leads to the 3-keto-5-hydroxy intermediate (4) depicted in FIG. 1.

The resulting 3-keto-5-hydroxy intermediate (4) may be dehydrated by acid or base catalyzed dehydration of the 5-hydroxy substituent to give the 3-keto-4-ene intermediate (5). Base catalyzed elimination my be effected by the treatment with an alkali metal alkyloxide (e.g, sodium methoxide). Other bases include tertiary amines (triethyamine, pyridine, etc.), alkali metal hydroxides in water and/or alcohol, or carbonate bases (e.g., K ₂ CO ₃ ).

Treatment of the 3-keto-4-ene intermediate (5) with a suitable oxidant yields drospirenone. Suitable oxidants include, but are not limited to chromium based oxidants (CrO ₃ /pyridine, Jones reagent, pyridinium dichromate (PDC), pyridinium chlorochromate (PCC), etc.), IBX, KMnO ₄ , MnO ₂ , RuO ₄ and 2,2,6,6-Tetramethylpiρeridine-l-oxyl (TEMPO) or derivatives of TEMPO (e.g., 4- hydroxy-TEMPO, 4-acetamido-TEMPO, 4-methoxy-TEMPO, 4-benzyl-TEMPO, and polymer- supported TEMPO). Further details regarding TEMPO oxidations of steroidal compounds is described in U.S. Patent No. 2007/0049747 to Seilz et al., which is incorporated herein by reference. . An advantage of the synthesis depicted in FIG. 1 is that the propargyl group acts as a protecting group to inhibit formation of the 17-spirolactone substituent during oxidation of the 3-hydroxy substituent. After the oxidation of the 3-hydroxy substituent is accomplished, the propargyl group may be reduced to its saturated form. The base catalyzed elimination of the 5-hydroxy group to form the 3-keto-4-ene portion of drospirenone may be performed without any concern for isomerization, since the spirolactone cannot be formed under the basic elimination conditions until the propargyl alcohol is oxidized. Another example of a synthesis of drospirenone is depicted in FIG. 2. FIG. 2 depicts a propargyl alcohol anion addition to the 17-keto substituent of the intermediate (1). R ¹ and R ² of intermediate (1) may be H, Si(R ⁵ ) ₃ , C(R ⁶ ) ₂ (OR ⁵ ) or CR ⁶ (OR ⁵ ) ₂ where each R ⁵ is independently alkyl, phenyl, or benzyl, and each R is independently alkyl or hydrogen. The propargyl alcohol anion has the structure: ^" C≡CZ, where Z is CN or CO ₂ R ⁴ ; where R ³ is independently alkyl, Si(R ⁵ ) ₃ , ϋr ^" CH(OR ⁵ ) ₂ rpheήyl, ^" θjrbenzylr ^" arld ^{^} eacrr R ⁴ arϊd ^~ R ^5~ is !MφeTitleiϊtly ^" hyclfogen, ^" alkyl,^phenyr, ^{^} benzyl, or an alkali metal. A lithium or potassium anion of the propargyl alcohol may be generated in situ using know methods as described above, all of which are incorporated herein by reference.

Reaction of the propargyl alcohol anion with intermediate (V) generates the 17-hydroxy addition product (2). The 17-hydroxy addition product (2) may be hydrogenated in the presence of a suitable catalyst (e.g., Pd, Pt, Rh, Ru, Ir, Ni, and Raney Nickel) to give the saturated intermediate (7).

Examples of suitable catalysts include, but are not limited to Pd/C and rhodium phosphine catalysts. The resulting hydrogenated intermediate (7) may be treated with an oxidant to oxidize the

3 -hydroxy substituent without effecting formation of the 17-spirolactone. Suitable oxidants include, but are not limited to chromium based oxidants (CrCVpyridine, Jones reagent, pyridinium dichromate (PDC), pyridinium chlorochromate (PCC), etc.), IBX, KMnO ₄ , MnO ₂ , RuO ₄ and

2,2,6,6-Tetramethylpiperidine-l-oxyl (TEMPO) or derivatives of TEMPO (e.g., 4-hydroxy-

TEMPO, 4-acetamido-TEMPO, 4-methoxy-TEMPO, 4-benzyl-TEMPO, and polymer-supported

TEMPO). Further details regarding TEMPO oxidations of steroidal compounds is described in U.S. Patent No. 2007/0049747 to Seilz et al., which is incorporated herein by reference. Oxidation of the

3-hydroxy substituent leads to the 3-keto~5-hydroxy intermediate (8) depicted in FIG. 2.

The resulting 3-keto-5-hydroxy intermediate (8) may be converted to drospirenone in a two step process, hi the first step, treatment with an aqueous base effects both dehydration of the 5 hydroxy substituent and hydrolysis of the -Z group (either -CN or CO ₂ R ⁴ ). Suitable bases include alkali metal hydroxides in water and/or a water/alcohol mixture, or carbonate bases (e.g., K ₂ CO ₃ ) in water or a water/alcohol mixture. Acidification of the resulting intermediate 3-keto-4-ene using an acid (e.g., an organic acid such as acetic acid) results in drospirenone.

Another example of a synthesis of drospirenone is depicted in FIG. 3. FIG. 3 depicts a

1 0 propargyl alcohol anion addition to the 17-keto substituent of the intermediate (V). R and R of intermediate (V) may be H, Si(R ⁵ ) ₃ , C(R ⁶ ) ₂ (OR ⁵ ) or CR ⁶ (OR ⁵ ) ₂ where each R ⁵ is independently alkyl, phenyl, or benzyl, and each R ⁶ is independently alkyl or hydrogen. The propargyl alcohol anion has the structure: ^" C≡CZ, where Z is CN or CO ₂ R ⁴ ; where R ³ is independently alkyl, Si(R ⁵ ) ₃ , or CH(OR ⁵ ) ₂ , phenyl, or benzyl; and each R ⁴ and R ⁵ is independently hydrogen, alkyl, phenyl, benzyl, or an alkali metal. A lithium or potassium anion of the propargyl alcohol may be generated in situ using know methods as described above, all of which arelncorporated herein by reference. Reaction of the propargyl alcohol anion with intermediate (1) generates the 17-hydroxy addition product (2).

The resulting addition product (2) may be treated with an oxidant to oxidize the 3-hydroxy substituent without effecting formation of the 17-spirolactone. Suitable oxidants include, but are 5 not limited to chromium based oxidants (CrOs/pyridine, Jones reagent, pyridinium dichromate (PDC), pyridinium chlorochromate (PCC), etc.), IBX, KMnO ₄ , MnO ₂ , RuO ₄ and 2,2,6,6- Tetramethylpiperidine-1-oxyl (TEMPO) or derivatives of TEMPO (e.g., 4-hydroxy-TEMPO, 4- acetamido-TEMPO, 4-methoxy-TEMPO, 4-benzyl-TEMPO, and polymer-supported TEMPO). Further details regarding TEMPO oxidations of steroidal compounds is described in U.S. Patent No.

10 2007/0049747 to Seilz et al, which is incorporated herein by reference. Oxidation of the 3-hydroxy substituent leads to the 3-keto-5-hydroxy intermediate (9) depicted in FIG. 2.

The 3-keto-5-hydroxy intermediate (9) may be hydrogenated in the presence of a suitable catalyst (e.g., Pd, Pt, Rh, Ru, Ir, Ni, and Raney Nickel) to give the saturated intermediate (8). Examples of suitable catalysts include, but are not limited to Pd/C and rhodium phosphine catalysts.

15 The resulting saturated intermediate (8) may be converted to drospirenone in a two step process, hi the first step, treatment with an aqueous base effects both dehydration of the 5 hydroxy svibstituent and hydrolysis of the -Z group (either -CN or CO ₂ R ⁴ ). Suitable bases include alkali metal hydroxides in water and/or a water/alcohol mixture, or carbonate bases (e.g., K ₂ CO ₃ ) in water or a water/alcohol mixture. Acidification of the resulting intermediate 3-keto-4-ene using an acid

20 (e.g., an organic acid such as acetic acid) results in drospirenone.

Another example of a synthesis of drospirenone is depicted in FIG. 4. FIG. 4 depicts a propargyl alcohol anion addition to the 17-keto substituent of the intermediate (1). R ¹ and R ² of intermediate (1) may be H, Si(R ⁵ ) ₃ , C(R ⁶ ) ₂ (OR ⁵ ) or CR ⁶ (OR ⁵ ) ₂ where each R ⁵ is independently alkyl, phenyl, or benzyl, and each R ⁶ is independently alkyl or hydrogen. The propargyl alcohol

25 anion has the structure: ^" C≡CZ, where Z is CN or CO ₂ R ⁴ ; where R ³ is independently alkyl, Si(R ⁵ ) ₃ , or CH(OR ⁵ ) ₂ , phenyl, or benzyl; and each R ⁴ and R ⁵ is independently hydrogen, alkyl, phenyl, benzyl, or an alkali metal. A lithium or potassium anion of the propargyl alcohol may be generated in situ using know methods as described above, all of which are incorporated herein by reference. Reaction of the propargyl alcohol anion with intermediate (1) generates the 17-hydroxy addition

^~ 30 ^~ product Q) ^~ The resulting addition product (2) may be treated with an oxidant to oxidize the 3-hydroxy substituent without effecting formation of the 17-spirolactone. Suitable oxidants include, but are not limited to chromium based oxidants (CrCVpyridine, Jones reagent, pyridinium dichromate (PDC), pyridinium chlorochromate (PCC), etc.), IBX, KMnO ₄ , MnO ₂ , RuO ₄ and 2,2,6,6- Tetramethylpiperidine-1-oxyl (TEMPO) or derivatives of TEMPO (e.g., 4-hydroxy-TEMPO, A- acetamido-TEMPO, 4-methoxy-TEMPO, 4-benzyl-TEMPO, and polymer-supported TEMPO). Further details regarding TEMPO oxidations of steroidal compounds is described in U.S. Patent No. 2007/0049747 to Seilz et al., which is incorporated herein by reference. Oxidation of the 3-hydroxy substituent leads to the 3-keto-5-hydroxy intermediate (9) depicted in FIG. 2. The resulting 3-keto-5-hydroxy intermediate (9) may be dehydrated by acid or base catalyzed dehydration of the 5-hydroxy substituent to give the 3-keto-4-ene intermediate (10). Base catalyzed elimination may be effected by the treatment with an alkali metal alkyloxide (e.g, sodium methoxide). Other bases include tertiary amines (triethylamine, pyridine, etc.), alkali metal hydroxides in water and/or alcohol, or carbonate bases (e.g., K ₂ CO ₃ ). Acid catalyzed elimination may be effected by the use of a mineral acid in a water/alcohol mixture. For example, acid catalyzed dehydration may be performed using a mixture of sulfuric acid in methanol.

The 3-keto-5-hydroxy intermediate (10) may be hydrogenated in the presence of a a suitable catalyst (e.g., Pd, Pt, Rh, Ru, Ir, Ni, and Raney Nickel) to give the saturated intermediate (11). Examples of suitable catalysts include, but are not limited to Pd/C and rhodium phosphine catalysts. The resulting saturated intermediate (11) may be converted to drospirenone in a two step process. In the first step, treatment with an aqueous base effects both dehydration of the 5 hydroxy substituent and hydrolysis of the -Z group (either -CN or CO ₂ R ⁴ ). Suitable bases include alkali metal hydroxides in water and/or a water/alcohol mixture, or carbonate bases (e.g., K ₂ CO ₃ ) in water or a water/alcohol mixture. Acidification of the resulting intermediate 3-keto-4-ene using an acid (e.g., an organic acid such as acetic acid) results in drospirenone.

In an alternate embodiment, drospirenone may be synthesized via an oxirane. FIG. 5 depicts a synthesis in which intermediate (1) is converted to an oxirane by the use of a methylene ylide. R ¹ and R ² of intermediate (1) may be H, Si(R ⁵ ) ₃ , C(R ⁶ ) ₂ (OR ⁵ ) or CR ⁶ (OR ⁵ ) ₂ where each R ⁵ is independently alkyl, phenyl, or benzyl, and each R is independently alkyl or hydrogen. Methylene ylides that may be used include sulfur ylides and selenium ylides. Sulfur ylides include, but are not limited to dimethyloxosulfonium methylide, (CHs) ₂ SOCH ₂ , also known as the Corey-Chaykovsky reagent ("CCR"), dimethylsulfonium methylide, and (CHs) ₂ SCH ₂ . CCR may be obtained from trimethyl sulfoxonium iodide, obtained by reaction of DMSO and methyl iodide, reacted with a strong base such as sodium hydride to generate CCR in situ. Selenium ylides include, but are not limited, PhSeCH ₂ and MeSeCH ₂

The resulting oxirane is reacted with a carbanion having the structure ^" CH-Z, where Z is CN or CO ₂ R ⁴ ; where R ⁴ is hydrogen, alkyl, phenyl, benzyl, or an alkali metal. A lithium or potassium anion of may be generated in situ using know methods. Reaction of the carbanion with intermediate (12) generates the 17-hydroxy addition product (13).

The resulting addition product (13) may be treated with an oxidant to oxidize the 3-hydroxy substituent without effecting formation of the 17-spirolactone. Suitable oxidants include, but are not limited to chromium based oxidants (CrOa/pyridine, Jones reagent, pyridinium dichromate (PDC), pyridinium chlorochromate (PCC), etc.), IBX, KMnO ₄ , MnO ₂ , RuO ₄ and 2,2,6,6- Tetramethylpiperidine-1-oxyl (TEMPO) or derivatives of TEMPO (e.g., 4-hydroxy-TEMPO, 4- acetamido-TEMPO, 4-methoxy-TEMPO, 4-benzyl-TEMPO, and polymer-supported TEMPO). Further details regarding TEMPO oxidations of steroidal compounds is described in U.S. Patent No. 2007/0049747 to Seilz et al., which is incorporated herein by reference. Oxidation of the 3-hydroxy substituent leads to the 3-keto-5-hydroxy intermediate (14) depicted in FIG. 2. The resulting 3-keto-5-hydroxy intermediate (14) may be converted to drospirenone in a two step process, hi the first step, treatment with an aqueous base effects both dehydration of the 5 hydroxy substituent and hydrolysis of the -Z group (either -CN or CO ₂ R ⁴ ). Suitable bases include alkali metal hydroxides in water and/or a water/alcohol mixture, or carbonate bases (e.g., K ₂ CO ₃ ) in water or a water/alcohol mixture. Acidification of the resulting intermediate 3-keto-4-ene using an acid (e.g., an organic acid such as acetic acid) results in drospirenone.

The methods described above have lead to a number of compounds that may be used to synthesis drospirenone. In an embodiment, drospirenone may be synthesized from any compound having the structure 15:

15

where Z is CN or CO ₂ R ⁴ ; R ⁷ Is -OR ¹ Or =O;

R ⁸ is H and R ⁹ is -OR ² or R ¹ and R ² together form a double bond; R ¹⁰ , R ¹¹ , R ¹² , and R ¹³ are H or R ¹⁰ , R ¹¹ , R ¹² , and R ¹³ together form a triple bond; where each R ¹ and R ² is independently H, Si(R ⁵ ) ₃ , C(R ⁶ ) ₂ (OR ⁵ ) or CR ⁶ (OR ⁵ ) ₂ ; where each R ⁴ and R ⁵ is independently hydrogen, alkyl, phenyl, benzyl, or an alkali metal; and each R ⁶ is independently alkyl or hydrogen. hi an embodiment, the compound has the structure (16):

16

where Z is CN or CO ₂ R ⁴

R ⁷ is -OR ¹ or =0;

R ⁸ is H and R ⁹ is -OR ² or R ¹ and R ² together form a double bond; where each R ¹ and R ² is independently H, Si(R ⁵ ) ₃ , C(R ⁶ ) ₂ (OR ⁵ ) or CR ⁶ (OR ⁵ ) ₂ ; where each R ⁴ and R ⁵ is independently hydrogen, alkyl, phenyl, benzyl, or an alkali metal; and each R ⁶ is independently alkyl or hydrogen. In another embodiment, the compound has the structure (17):

17

where Z is CN or CO ₂ R ⁴ ; R ⁷ is -OR ¹ or =0;

R ⁸ is H and R ⁹ is -OR ² or R ¹ and R ² together form a double bond; where each R ¹ and R ² is independently H, Si(R ⁵ ) ₃ , C(R ⁶ ) ₂ (OR ⁵ ) or CR ⁶ (OR ⁵ ) ₂ ; where each R ⁴ and R ⁵ is independently hydrogen, alkyl, phenyl, benzyl, or an alkali metal; and each R ⁶ is independently alkyl or hydrogen.

Specific examples of compounds that may be used for the synthesis of drospirenone include the following:

18 19

22 23

Where in each of compounds (18) - (23), Z is CN or CO ₂ R ⁴ ; and where R ⁴ is hydrogen, alkyl, phenyl, benzyl, or an alkali metal.

EXAMPLES

The following examples are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventor to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. FIGURE 1 - Experimental example

21

2a

A solution of compound (1) (5g, 15.2mmol) and tert-butyldimethyl (2-propynyloxy)silane (2.83g, 16.7mmol) in 75 ml of dry THF was added dropwise through an addition funnel to a precooled slurry of potassium tert-butoxide (8.49g, 75.7mmol) at -10 C. A thick white precipitate is formed during the addition and the resulting mixture was stirred for an hour at 0 C. TLC analysis (70% EtOAc/Hexanes) showed completion of the reaction and showed a less polar product. The reaction was quenched by the addition of ice water (100ml) and neutralized by adding acetic acid (4.3ml). The THF layer was separated and the aqueous layer was extracted with EtOAc (2 x 50ml). The combined organic layers were washed with water (2 x 100ml), brine (100ml) and dried over anhydrous sodium sulfate. The solvent was removed under vacuum to afford compound (2a) (7.5g, 99.2%) as a solid which was used in the next step without any purification. NMR (CDCl ₃ ) δ 0.139 (s, 6H, Si-CH ₃ ), 0.385 (m, IH), 0.628 (m, IH), 0.857 (s, 18-Me), 0.896 (s, 19-Me), 0.918 (s, 3H, Si-CH ₃ ), 0.927 (s, 6H, Si-CH ₃ ), 4.05 (s, IH), 4.428 (s, 2H, -OCH ₂ ) FTIR(ATR): 3311, 3017, 2929, 2858, 2270, 1058 cm ⁴

Compound (2a) (5g, 9.98mmol) was dissolved in 100 ml of ethyl acetate in a Parr hydrogenation bottle and was mixed with 10% palladium on charcoal (Ig, 0.09mmol). This mixture was hydrogenated on a Parr apparatus at a pressure of 20 psi for 90 minutes. The catalyst was filtered and washed with ethyl acetate. The solvent was removed in vacuo to afford compound (3a) as a colorless foam (5.01g, 99%).

NMR (CDCl ₃ ) δ 0.0758 (s, 6H, Si-CH ₃ ), 0.283 (m, IH), 0.628 (m, IH), 0.856 (s, 18-Me), 0.893 (s, 19-Me), 0.918 (s, 9H, Si-CH ₃ ), 3.69 (m, 2H), 4.05 (s, IH). FTIR(ATR): 3374, 3017, 2929, 2858, 1259, 1091, 1049, 835 cm ^"1

Chromium trioxide (4.95g, 49.5mmol) was added to a solution of pyridine (7.83g, 99.05mmol) in anhydrous dichloromethane (100 ml). The resulting mixture was stirred for 15 minutes during which time the color changed to burgundy. A solution of compound (3a) (5g, 9.90mmol) in 50 ml of dichloromethane was added and the mixture was stirred at room temperature for 6h. The excess oxidizing agent was quenched by adding isopropanol. The reaction mixture was diluted with MTBE (50 ml) and was passed through a short pad of Celite. The solid was washed again with 2:1 MTBE-CH ₂ Cl ₂ (50ml x2). The solvent was removed in vacuo to give a residue which was dissolved in 100 ml of EtOAc, was washed with water, and dried over anhydrous sodium sulfate. The solvent was removed in vacuo to afford compound (4a) as a pale yellow foam (4.5g, 90.3%).

NMR (CDCl ₃ ) δ 0.08 (s, 6H, Si-CH ₃ ), 0.31 (m, IH), 0.914 (s, 9H, Si-CH ₃ ), 0.931 (s, 6H, 18-Me, 19-Me) 3.70 (m, 2H). FTIR (ATR): 3399, 3022, 2950, 2929, 2862, 1708, 1649, 1259, 1041 cm ^"1

A solution of compound (4a) (5g, 9.94mmol) in 50ml of MeOH was refluxed with NaOH (397mg, 9.94mmol) for 3h. When the reaction was over, as shown by TLC, the reaction mixture was cooled to room temperature and added to ice cold water (150 ml). The mixture was extracted with ethyl acetate (3 x 50 mL). The combined EtOAc layers were washed with water (100ml) brine (50ml) and dried over sodium sulfate. The solvent was removed in vacuo to afford compound (5) as a colorless amorphous solid (4.5g, 92%). NMR (CDCl ₃ ) δ 0.05 (s, 6H, Si-CH ₃ ), 0.296 (m, IH), 0.886 (s, 9H, Si-CH ₃ ), 0.908 (s, 3H, 18-Me), 1.07 (s, 3H, 19-Me), 3.68 (m, 2H), 5.95 (s, IH). FTIR(ATR): 3450, 3009, 2950, 2858, 1653, 1603, 1095 cm ^"1

Drospirenone

A solution of compound (5a) (5g, 9.94mmol) in 30ml of acetone was cooled to -15 C as a 2.7M solution of Jones reagent (3.68ml, 9.94mmol) was added drop wise. The reaction mixture was stirred at 0 C for 2h, during this time TLC showed completion of the reaction. The reaction was quenched by adding isopropanol and diluted with water. The reaction mixture was extracted with EtOAc. The combined EtOAc layers were washed with water, sat. NaHCO ₃ and brine. The EtOAc layers-were dried over-sodium-sulfate-and-solvent- was -removed-by -vacuum -to-afford-cmde drospirenone as a pale yellow foam (3g, 82%) Recrystallization from acetone-hexane gave 1.5g of pure drospirenone as white solid.

NMR (CDCl ₃ ) δ 0.0548 (m, IH), 0.88( m, IH), 1.008(s, 3H, 18-Me), 1.11 (s, 3H, 18-Me), 6.03 (s, IH). FTIR(ATR): 3025, 2971, 2942, 1763, 1654, 1590, 1186 cm ^'1 FIGURE 2 - Experimental example

2b

Lithium hexamethyldisilylamide (LiHMDS) 1.0 M/THF (75.7mL, 75.7mmol) was introduced into a 50OmL, 3 -neck flask equipped with an addition funnel and a pierced septa for the introduction of a thermocouple probe. The mixture was diluted with THF (25mL). The solution was stirred (Teflon paddle) and chilled to an internal temperature of -72 ⁰ C. A THF (75mL) solution of ketodiol (5g, 15.13mmol) containing ethyl propiolate (3.07mL, 30.26mmol) was added dropwise over 1 hour while not allowing the temperature to rise above -65 ⁰ C. Upon completion of the addition the mixture was stirred for 3 hrs while allowing the temperature to warm slowly to -6O ⁰ C. Finally, the mixture was warmed to -4O ⁰ C over 1 hour.

The mixture was quenched through the addition of acetic acid (4.25mL)/water (5.OmL) followed by the addition of saturated ammonium chloride solution (10OmL). The mixture was stirred for 3 min and then transferred to a separatory funnel. The layers were separated and the upper, THF layer was diluted with ethyl acetate (75mL). The organic phase was washed with water (3 x 10OmL) and brine (I x 10OmL). AU the aqueous washes were extracted with ethyl acetate (2 x 3OmL). The combined organic extract was dried over sodium sulfate, filtered, and evaporated in vacuo (45 ⁰ C) to afford a thick oil. Dichloromethane (ca, 35mL) was added and evaporated in vacuo. The flask was cooled slightly and dichloromethane (33ml) was added to give a solid mass. The solid was broken up and stirred until a homogeneous slurry was obtained. Hexanes (35mL) was added slowly to the stirred mixture and the mixture was stored at 2-4 C overnight. The solid was filtered, washed with 30% dichloromethane/hexanes, and dried in vacuo at ambient temperature for 4 hours to give (2b) 5.86g (90.4%) of a white powder.

7b

Compound (2b) (5.Og, 11.67mmol) was dissolved in THF (5OmL) and 5% Pd/C (622mg,

0.29mmol Pd) was added and the mixture was shaken at 15 psi H ₂ for 2 hours. The mixture was diluted with ethyl acetate (25mL) and filtered through a pad of Celite. The filter pad was washed with ethyl acetate (3 x 25mL) and the filtrate was evaporated to dryness to afford 5.Og (99.1%) of triol (7b) as a stable foam.

8b

Compound (7b) (5.Og, 11.56mmol) was dissolved in dichloromethane (5OmL) and the solution was stirred vigorously and chilled to -15 ⁰ C (NaCl/ice) and TEMPO (45.16mg, 0.29mmol, 2.5 mol%) was added. The mixture was treated dropwise over about 15-20 min. with a mixture of sodium hypochlorite (12.5%) (11.17mL, 23.12mmol) in water (8.OmL) containing potassium bicarbonate (833mg, 8.32mmol). The mixture was allowed to warm to 0 C for 1.25 hrs. Analysis of- the reaction- by^FL(3-(60%-EtΘAc/hex)- shows -the appearance of a slightly less polar product- (ΔRf=0.8 cm). The mixture was chilled to -5 C and was quenched through the dropwise addition (ca 10-15 min) of a water (15.OmL) solution of sodium phosphate (1.27g, 7.75mmol) and sodium metabisulfite (1.1 Og, 5.78mmol). The layers were separated and the dichloromethane solution was washed with water (2x) and brine. All aqueous washes were extracted with additional dichloromethane (2 x 15mL). The combined dichloromethane extract was dried over sodium sulfate, filtered, and evaporated to give 4.88g (98.08%) of ketone (8b) as a stable foam.

Drospirenone

Compound (8b) was added to a methanol (1OmL) solution containing 8.0 M KOH solution

(6.3mL, 50.36mmol) preheated to 60 C. The solution was heated at reflux for 2.5 hours. The mixture was chilled in an ice bath and treated with acetic acid (36mL) and water (5.OmL). The solution was stirred at 50-60 C for 15 hours. The volatiles were evaporated in vacuo and the acetic acid solution was poured into cold water (15OmL) to give a white precipitate. The aqueous mixture was extracted with ethyl acetate (2 x 10OmL). The ethyl acetate extracts were washed with water (2x), saturated sodium bicarbonate solution, and brine. The combined ethyl acetate extract was dried over sodium sulfate. Evaporation of the solvent gave a yellow foam. Trituration of the foam with acetone/hexane followed by evaporation gave 4.27g (92.62%) of a light yellow solid. Recrystallization of the solid from acetone/hexanes gave 3.07g of drospirenone with an HPLC purity of 99.66%. Evaporation of the mother liquor and recrystallization of the residue affords an additional 0.54g of slightly impure drospirenone. FIGURE 3 - Experimental example

2c

Lithium hexamethyldisilylamide (LiHMDS) 1.0 M/THF (75.7mL, 75.7mmol) was introduced into a 50OmL, 3 -neck flask equipped with an addition funnel and a pierced septa for the introduction of a thermocouple probe. The mixture was diluted with THF (25mL). The solution was stirred (Teflon paddle) and chilled to an internal temperature of -72 ⁰ C. A THF (75mL) solution of ketodiol (5g, 15.13mmol) containing ethyl propiolate (3.07mL, 30.26mmol) was added dropwise over 1 hour while not allowing the temperature to rise above -65 ⁰ C. Upon completion of the addition the mixture was stirred for 3 hrs while allowing the temperature to warm slowly to -6O ⁰ C. Finally, the mixture was warmed to -4O ⁰ C over 1 hour.

The mixture was quenched through the addition of acetic acid (4.25mL)/water (5.OmL) followed by the addition of saturated ammonium chloride solution (10OmL). The mixture was stirred for 3 min and then transferred to a separatory funnel. The layers were separated and the upper, THF layer was diluted with ethyl acetate (75mL). The organic phase was washed with water (3 x 10OmL) and brine (I x 10OmL). All the aqueous washes were extracted with ethyl acetate (2 x 3OmL). The combined organic extract was dried over sodium sulfate, filtered, and evaporated in vacuo (45 ⁰ C) to afford a thick oil. Dichloromethane (ca. 35mL) was added and evaporated in vacuo. The flask was cooled slightly and dichloromethane (33ml) was added to give a solid mass. The solid was broken up and stirred until a homogeneous slurry was obtained. Hexanes (35mL) was added slowly to the stirred mixture and the mixture was stored at 2-4 C overnight. The solid was filtered, washed with 30% dichloromethane/hexanes, and dried in vacuo at ambient temperature for 4 hours to give (2c) 5.86g (90.4%) of a white powder.

9c

Propiolate adduct (2c) (5.86g, 13.67mmol) was suspended in dichloromethane (6OmL). The mixture was stirred vigorously and chilled to -15 ⁰ C (NaCl/ice) and TEMPO (54mg, 0.35mmol, 2.5mol%) was added. The mixture was treated dropwise over about 15-20 min. with a mixture of sodium hypochlorite (12.5%) (13.2mL, 27.34mmol) in water (8.OmL) containing potassium bicarbonate (985mg, 9.84mmol). During the addition of the hypochlorite solution, a 5-8 C temperature rise was observed and the mixture became yellow. The mixture was allowed to warm to at 0 C for 2 hrs. Analysis of the reaction by TLC (60% EtO Ac/hex) shows the appearance of a slightly less polar product (ARf=O.8 cm). The mixture was chilled to -5 C and was quenched through the dropwise addition (ca 10-15 min) of a water (15.OmL) solution of sodium phosphate (1.5Og, 9.16mmol) and sodium metabisulflte (1.3Og, 6.84mmol). Once again, a temperature rise of 5-8 C was observed and the yellow color was quenched. The layers were separated and the dichloromethane solution was washed with water (2x) and brine. All aqueous washes were extracted with additional dichloromethane (2 x 15mL). The combined dichloromethane extract was dried over sodium sulfate and the bulk of the solvent was evaporated in vacuo. Upon the observation of solids in the mixture during the evaporation, the evaporation was discontinued and the residue in the flask diluted with MTBE (35mL). While stirring, the mixture was slowly diluted with hexanes (35mL). The mixture was then chilled in an ice bath for 30 min. The solid was filtered, washed with 25% MTBE/hexane, and dried to give intermediate (9c) (4.98g, 85.31%) as a white solid.

NMR(CDCl ₃ ) δ 0.462 (q, IH), 0.699 (m, IH), 0.924 (s, 18-Me), 0.952 (s, 19-Me), 1.338 (t, J=7Hz, OCH ₂ CH ₃ ), 2.517 (d, IH), 3.021(d, IH), 4.269 (t, OCH ₂ CH ₃ ) ppm. FTIR(ATR): 3493, 3252, 2948, 2226, 1697, 1241 cm ^"1 .

8c

Alkynyl ketone (9c) (5.37g, 12.59mmol) was dissolved in THF (27mL) in a 25OmL shaker bottle. 5% Pd/C (670mg, 2.5mol%) was added to the solution and the mixture was shaken under a hydrogen pressure of 15 psi. Over approximately 30 min, there was observed a rapid up take of hydrogen. The pressure was continually adjusted to 15 psi until the uptake of hydrogen ceased and was shaken for a total of 1.5 hrs. The mixture was diluted with a small amount of methanol and filtered through Celite. The filter pad was washed with methanol (ca.3 x 25mL).

NMR(CDCl ₃ ) δ 0.353 (q, IH), 0.704 (m, 2H), 0.930 (s, 18-Me), 0.933 (s, 19-Me), 1.279 (t, J=7Hz, OCH ₂ CH ₃ ), 2.480 (d, IH), 2.672 (m, 2H), 3.981(d, IH), 4.162 (t, OCH ₂ CH ₃ ) ppm. FTIR(ATR): 3465, 2946, 1712, cm ^"1 .

Drospirenone

The filtrate containing compound (8c), described above, was added in one portion to a methanol (1OmL) solution containing 8.0 M KOH solution (6.3mL, 50.36mmol) preheated to 60 C. The solution was heated at reflux for 2.5 hours. The mixture was chilled in an ice bath and treated with-acetic-acid-(36mL)-and-water-(5.0mL) _^ -The-solution-was stirred-at -50-60 C-for- 45-hours.— The- volatiles were evaporated in vacuo and the acetic acid solution was poured into cold water (15OmL) to give a white precipitate. The aqueous mixture was extracted with ethyl acetate (2 x 10OmL). The ethyl acetate extracts were washed with water (2x), saturated sodium bicarbonate solution, and brine. The combined ethyl acetate extract was dried over sodium sulfate. Evaporation of the solvent gave a yellow foam. Trituration of the foam with acetone/hexane followed by evaporation gave 4.27g (92.62%) of a light yellow solid. Recrystallization of the solid from acetone/hexanes gave 3.07g of drospirenone with an HPLC purity of 99.66%. Evaporation of the mother liquor and recrystallization of the residue affords an additional 0.54g of slightly impure drospirenone. FIGURE 4 - Experimental example

2d

Lithium hexamethyldisilylamide (LiHMDS) 1.0 M/THF (75.7mL, 75.7mmol) was introduced into a 50OmL, 3-neck flask equipped with an addition funnel and a pierced septa for the introduction of a thermocouple probe. The mixture was diluted with THF (25mL). The solution was stirred (Teflon paddle) and chilled to an internal temperature of -72 ⁰ C. A THF (75mL) solution of ketodiol (5g, 15.13mmol) containing ethyl propiolate (3.07mL, 30.26mmol) was added dropwise over 1 hour while not allowing the temperature to rise above -65 ⁰ C. Upon completion of the addition the mixture was stirred for 3 hrs while allowing the temperature to warm slowly to -6O ⁰ C. Finally, the mixture was warmed to -4O ⁰ C over 1 hour.

The mixture was quenched through the addition of acetic acid (4.25mL)/water (5.OmL) followed by the addition of saturated ammonium chloride solution (10OmL). The mixture was stirred for 3 min and then transferred to a separatory funnel. The layers were separated and the upper, THF layer was diluted with ethyl acetate (75mL). The organic phase was washed with water (3 x 10OmL) and brine (1 x 10OmL). All the aqueous washes were extracted with ethyl acetate (2 x 30ϊnE)^Tlie ^" combined organic extract ^wa¥ ^~ dϊied ^" over sodiumlmlfate7 fϊltered7and evapofated ^" /?f vacuo (45 ⁰ C) to afford a thick oil. Dichloromethane (ca. 35mL) was added and evaporated in vacuo. The flask was cooled slightly and dichloromethane (33ml) was added to give a solid mass. The solid was broken up and stirred until a homogeneous slurry was obtained. Hexanes (35mL) was added slowly to the stirred mixture and the mixture was stored at 2-4 C overnight. The solid was filtered, washed with 30% dichloromethane/hexanes, and dried in vacuo at ambient temperature for 4 hours to give (2d) 5.86g (90.4%) of a white powder.

9d

Propiolate adduct (2d) (5.86g, 13.67mmol) was suspended in dichloromethane (60 mL). The mixture was stirred vigorously and chilled to -15 ⁰ C (NaCl/ice) and TEMPO (54mg, 0.35mmol, 2.5mol%) was added. The mixture was treated dropwise over about 15-20 min. with a mixture of sodium hypochlorite (12.5%) (l3.2mL, 27.34mmol) in water (8.OmL) containing potassium bicarbonate (985mg, 9.84mmol). During the addition of the hypochlorite solution, a 5-8 C temperature rise was observed and the mixture became yellow. The mixture was allowed to warm to at 0 C for 2 hrs. Analysis of the reaction by TLC (60% EtO Ac/hex) shows the appearance of a slightly less polar product (ΔR _f =0.8 cm). The mixture was chilled to -5 C and was quenched through the dropwise addition (ca 10-15 min) of a water (15.OmL) solution of sodium phosphate (1.50g, 9.16mmol) and sodium metabisulfite (1.3Og, 6.84mmol). Once again, a temperature rise of 5-8 C was observed and the yellow color was quenched. The layers were separated and the dichloromethane solution was washed with water (2x) and brine. All aqueous washes were extracted with additional dichloromethane (2 x 15mL). The combined dichloromethane extract was dried over sodium sulfate and the bulk of the solvent was evaporated in vacuo. Upon the observation of solids in the mixture during the evaporation, the evaporation was discontinued and the residue in the flask diluted with MTBE (35mL). While stirring, the mixture was slowly diluted with hexanes (35mL). The mixture was then chilled in an ice bath for 30 min. The solid was filtered, washed with 25% MTBE/hexane, and dried to give intermediate (9d) (4.98g, 85.31%) as a white solid.

NMR(CDCl ₃ ) δ 0.462 (q, IH), 0.699 (m, IH), 0.924 (s, 18-Me), 0.952 (s, 19-Me), 1.338 (t, J=7Hz, OCH ₂ CH ₃ ), 2.517 (d, IH), 3.021(d, IH), 4.269 (t, OCH ₂ CH ₃ ) ppm. FTIR(ATR): 3493, 3252, 2948, 2226, 1697, 1241 cm ^"1 .

1Od

Compound (9d) (5.Og) was dissolved in methanol (5OmL) and treated with 1.0 N sulfuric acid (1OmL). The mixture was heated to reflux for 3 hours, cooled, and neutralized through the addition of saturated sodium bicarbonate solution. Most of the methanol was evaporated in vacuo at ambient temperature and diluted with water. The aqueous mixture was extracted with ethyl acetate. The ethyl acetate extract was washed with water and brine, dried over sodium sulfate, filtered, and evaporated to give 4.95g of unsaturated ketone (IQd) as a stable foam.

Hd

Compound (IQd) (5.Og, 12.24mmol) was dissolved in degassed benzene (5OmL) and treated ^ith^hlόTolri¥(tπplϊeltylpho^hin^)rho^iurrr(I) ^{^} (2837 Inϊg7θ .3 lmmol^ndl:rreπre^ultmgTnixture was stirred in a hydrogen atmosphere for 10 hours. The solution was evaporated, reconstituted in 50% ethyl acetate/hexanes, and passed through a short column of neutral alumina. Evaporation of the solvent gave 4.95g of did) as a stable foam.

Drospirenone

Compound (lid) (4.95g, 12.01mmol) was dissolved in 10% aqueous methanol (5OmL) and solid potassium carbonate (4.98g, 36.04mmol) was added. The mixture was stirred at room temperature for 30 min and the bicarbonate was neutralized through the addition of acetic acid (2.06mL, 36.04mmol). The methanol was evaporated in vacuo at ambient temperature and diluted with water. The aqueous mixture was extracted with ethyl acetate. The ethyl acetate extract was washed with water and brine, dried over sodium sulfate, filtered, and evaporated to give 4.1Og (93%) of a semi solid. The material was dissolved in dichloromethane and evaporated in vacuo to give a stable foam. The foam was dissolved in ethyl acetate (5 mL) and allowed to stand overnight. The resulting solid was filtered, washed with cold ethyl acetate, and dried in vacuo to afford 2.86g (66%) of pure drospirenone. FIGURE 5 - Experimental example 1

Ie A dichloromethane (5OmL) solution of ketodiol (1) (5.Og, 15.13mmol) was treated with ethyl vinyl ether (7.24mL, 75.65mmol), followed by the addition of pyridinium tosylate (380mg, 1.15mmol). The solution was stirred at room temperature for 30 min. The dichloromethane solution was washed with water (2x), brine, and dried over sodium sulfate. Following filtration, evaporation of the solvent gave 6.14g of the 3-protected compound (Ie) as a stable foam.

12e

Compound (Ie) (6.14g, 15.13mmol) was dissolved in DMSO/THF (15mL/15mL), treated with trimethylsulfonium iodide (4.63g, 22.70mmol) and the mixture was chilled to -15 C. The mixture was treated portion wise with potassium t-butoxide (3.23g, 28.82mmol). The mixture was stirred at -15 C for 45 min and then poured into ice/water (200 mL). The aqueous mixture was extracted with ethyl acetate. The ethyl acetate extract was washed with water (2x) and brine, dried over sodium sulfate, and filtered. Evaporation of the solvent gave 6.21g (98.42%) of oxirane (12e) as a stable foam.

A THF (3OmL) solution of di-isopropyl amine (12.02mL, 85.03mmol) was chilled to -40 C and treated with butyl lithium (2.5 M/hexanes,_34.01mL _L 85.03mmol) and the mixture was stirred for 15 min. A THF (5mL) solution of acetonitrile (4.7mL, 90.79mmol) was added dropwise to the in situ generated lithium di-isopropylamide (LDA) solution to give a slurry of the acetonitrile anion. After stirring for 15 min at -4O ⁰ C, compound (12e) (6.21g, 14.91mmol) as a THF (25mL) solution was added dropwise over 10 min. The mixture was stirred for 30 min and then quenched through the addition of saturated ammonium chloride solution (21OmL). The mixture was extracted with ethyl acetate. The ethyl acetate extract was washed with water (3x) and brine, dried over sodium sulfate, and filtered. Evaporation of the solvent gave 7.07g of the addition product (13e) as a tacky foam.

14e

Compound l_3e (5.0g, 10.93mmol) was dissolved in acetone (25mL) and chilled to 0 C. The stirred solution was treated dropwise with 2.7M chromic acid (Jones Reagent) (7.OmL, 18.91mmol). After 1.5 hrs, the excess Cr (VI) was quenched through the addition of 2-propanol until the green color of Cr (IV) was evident. Water (300 mL) was added and the mixture was stirred until all the chromium salts were dissolved. The aqueous mixture was extracted with ethyl acetate. The ethyl acetate extract was washed with water (2x) and brine, dried over sodium sulfate, and filtered. Evaporation of the solvent gave 3.83g (96%) of ketone (14e) as a stable foam.

Drospirenone Compound (14e) (3.83g, 10.48mmol) was dissolved in methanol (38mL) and treated with 8.0 M KOH solution (7.OmL, 56mmol) and the mixture was heated at reflux for 5 hours. The mixture was cooled to 0 C and treated with acetic acid (15mL) and water (6mL) and the mixture was stirred at 50 C for 6 hours. The solvents were evaporated in vacuo and the residue was diluted with water (20OmL). The aqueous mixture was extracted with ethyl acetate. The ethyl acetate extract was washed with water (2x) and brine, dried over sodium sulfate, and filtered. Evaporation of the solvent gave 3.76g (94%) of crude drospirenone as a stable foam. The crude drospirenone was dissolved in 60% ethyl acetate/hexanes and passed through a short column of neutral alumina (10x w/w) and the column was eluted with the same solvent. Following evaporation of the solvent, 2.58g (65%) of crystalline drospirenone was obtained. Recrystallization from acetone/hexanes afforded pure drospirenone. FIGURE 5 - Experimental example 2

Intermediate (1) (5g, 15.13mmol) was dissolved in DMSO/THF (50mL/50mL), treated with trimethylsulfonium iodide (4.63g, 22.70mmol), and the mixture was chilled to -15 C. The mixture was treated portion wise with potassium t-butoxide (5.03g, 43.88mmol). The mixture was stirred at -15 C for 45 min and then poured into ice/water (20OmL). The aqueous mixture was extracted with ethyl acetate. The ethyl acetate extract was washed with water (2x) and brine, dried over sodium sulfate, and filtered. Evaporation of the solvent gave 5.11g (98%) of oxirane (12f) as a stable foam.

13f A THF (3OmL) solution of di-isopropyl amine (12.02mL, 85.03mmol) was chilled to 40 C and treated with butyl lithium (2.5 M/hexanes, 34.0ImL, 85.03mmol) and the mixture was stirred for 15 min. A THF (5mL) solution of acetonitrile (4.7mL, 90.79mmol) was added dropwise to the above lithium di-isopropylamide (LDA) solution to give a slurry of the acetonitrile anion. After stirring for 15 min at -40 C, compound (12f) (5.11g, 14.83mmol) as a THF (75mL) solution was added dropwise over 10 min. The mixture was stirred for 30 min and then quenched through the addition of saturated ammonium chloride solution (30OmL). The mixture was extracted with ethyl acetate. The ethyl acetate extract was washed with water (3x) and brine, dried over sodium sulfate, and filtered. Evaporation of the solvent gave 5.75 g of addition product (13f) as a tacky foam.

14f

Compound 13f (5.75g, 14.95mmol) was dissolved in acetone (25mL) and chilled to 0 C. The stirred solution was treated dropwise with 2.7M chromic acid (Jones Reagent) until the orange color of Cr (VI) persisted. After 1.5 hrs, the excess Cr (VI) was quenched through the addition of 2- propanol until the green color of Cr (IV) was evident. Water (30OmL) was added and the mixture was stirred until all the chromium salts were dissolved. The aqueous mixture was extracted with ethyl acetate. The ethyl acetate extract was washed with water (2x) and brine, dried over sodium sulfate, and filtered. Evaporation of the solvent gave 5.5g (96%) of ketone (14f) as a stable foam.

Drospirenone

5 Compound (14f) (5.5g, 14.38mmol) was dissolved in methanol (5OmL) and treated with 8.0

M KOH solution (9.35mL, 74.77mmol) and the mixture was heated at reflux for 5 hours. The mixture was cooled to 0 C and treated with acetic acid (25mL) and water (1OmL) and the mixture was stirred at 50 C for 6 hours. The solvents were evaporated in vacuo and the residue was diluted with water (30OmL). The aqueous mixture was extracted with ethyl acetate. The ethyl acetate

10 extract was washed with water (2x) and brine, dried over sodium sulfate, and filtered. Evaporation of the solvent gave 4.95g (94%) of crude drospirenone as a stable foam. The crude drospirenone was dissolved in 60% ethyl acetate/hexanes and passed through a short column of neutral alumina (10x w/w) and the column was eluted with the same solvent. Following evaporation of the solvent, 3.43g (65%) of crystalline drospirenone was obtained. Recrystallization from acetone/hexanes

15 afforded pure drospirenone.

In this patent, certain U.S. patents, U.S. patent applications, and other materials (e.g., articles) have been incorporated by reference. The text of such U.S. patents, U.S. patent applications, and other materials is, however, only incorporated by reference to the extent that no conflict exists between such text and the other statements and drawings set forth herein, hi the

20 event of such conflict, then any such conflicting text in such incorporated by reference U.S. patents, U.S. patent applications, and other materials is specifically not incorporated by reference in this patent.

Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to

-25- be eonstrued-as illustrative-only-and-is-for-the-purpose-of-teaching-those skilled-in the art the-general- manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as examples of embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims.