Process for the preparation of geminal ( (difluorocycloalkyl)methyl) amines

5 FIELD OF INVENTION

The present invention relates to a process of making a difluoro compound, and particularly to a process of making a difluoro compound containing an amino group.

BACKGROUND

Difluoro compounds containing an amino group are useful intermediates in the o synthesis of compounds having therapeutic effects. PCT publication No. WO2004/108688 describes a method of making one of these difluoro compounds containing an amino group, [(4,4-difluorocyclohexyl)methyl]amine. However, an improved process of making these compounds is still desirable.

DESCRIPTION OF THE EMBODIMENTS s In one aspect, the present invention provides a process of making a compound comprising: a first step of reacting a compound of formula I with (dialkylamino)sulfur trifluoride to form a first product,

0 I wherein R ¹ is selected from hydrogen, C^alkyl, C _2-6 alkenyl, halogenated C _1-6 alkyl, C^alkoxy, -OH, and amino; and n, m, and p are independently selected from 0, 1 and 2.

As used here, the term "C _m-n " or "C _m-n group" used alone or as a prefix, refers to any group having m to n carbon atoms.

The term "hydrocarbon" used alone or as a suffix or prefix, refers to any structure comprising only carbon and hydrogen atoms up to 14 carbon atoms. The term "hydrocarbon radical" or "hydrocarbyl" used alone or as a suffix or prefix, refers to any structure as a result of removing one or more hydrogens from a hydrocarbon.

The term "alkyl" used alone or as a suffix or prefix, refers to a saturated monovalent straight or branched chain hydrocarbon radical comprising 1 to about 12 carbon atoms. Illustrative examples of alkyls include, but are not limited to, C i-galkyl groups, such as methyl, ethyl, propyl, isopropyl, 2-methyl-l -propyl, 2-methyl-2-propyl, 2- methyl-1 -butyl, 3 -methyl- 1 -butyl, 2-methyl-3 -butyl, 2,2-dimethyl-l -propyl, 2-methyl-l- pentyl, 3-methyl-l-pentyl, 4-methyl-l-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl, 4- methyl-2-pentyl, 2,2-dimethyl-l -butyl, 3, 3 -dimethyl- 1 -butyl, 2-ethyl-l -butyl, butyl, isobutyl, t-butyl, pentyl, isopentyl, neopentyl, and hexyl, and longer alkyl groups, such as heptyl, and octyl. An alkyl can be unsubstituted or substituted with one or two suitable substituents.

The term "alkenyl" used alone or as suffix or prefix, refers to a monovalent straight or branched chain hydrocarbon radical having at least one carbon-carbon double bond and comprising at least 2 up to about 12 carbon atoms. The double bond of an alkenyl can be unconjugated or conjugated to another unsaturated group. Suitable alkenyl groups include, but are not limited to C _2-6 alkenyl groups, such as vinyl, allyl, butenyl, pentenyl, hexenyl, butadienyl, pentadienyl, hexadienyl, 2-ethylhexenyl, 2-propyl-2-butenyl, 4-(2-methyl-3- butene)-pentenyl. An alkenyl can be unsubstituted or substituted with one or two suitable substituents.

The term "cycloalkyl," used alone or as suffix or prefix, refers to a saturated monovalent ring-containing hydrocarbon radical comprising at least 3 up to about 12 carbon atoms. Examples of cycloalkyls include, but are not limited to, C _3-7 cycloalkyl groups, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and cycloheptyl, and saturated cyclic and bicyclic terpenes. A cycloalkyl can be unsubstituted or substituted by

one or two suitable substituents. Preferably, the cycloalkyl is a monocyclic ring or bicyclic ring.

The term "alkoxy" used alone or as a suffix or prefix, refers to radicals of the general formula -O-R, wherein R is selected from a hydrocarbon radical. Exemplary alkoxy includes methoxy, ethoxy, propoxy, isopropoxy, butoxy, t-butoxy, isobutoxy, cyclopropylmethoxy, allyloxy, and propargyloxy.

The term "amino" refers to -NH ₂ .

Halogen includes fluorine, chlorine, bromine and iodine.

"Halogenated," used as a prefix of a group, means one or more hydrogens on the group is replaced with one or more halogens.

"RT" or "rt" means room temperature.

The term "Ra-Ni" refers to Raney® nickel such as Raney® 2800 nickel.

In one embodiment, the (dialkylamino)sulfur trifluoride used in the process is selected from (dimethylamino)sulfur trifluoride, (diethylamino)sulfur trifluoride and (morpholino)sulfur trifluoride.

In another embodiment, R ¹ is selected from hydrogen and C^alkyl.

In a further embodiment, n, m and p are 1 and R ¹ is hydrogen.

In another embodiment, in the process of making a compound, the compound of formula I and (dialkylamino) sulfur trifluoride are reacted at a mole ratio between 1:10 and 10:1. Particularly, the mole ratio between the compound of formula I and

(dialkylamino)sulfur trifluoride are between 2: 1 and 1 :2. More particularly, the mole ratio is about 1:1.1.

In another embodiment, the first step of reacting the compound of formula I and (dialkylamino)sulfur trifluoride is carried out at a temperature between -25 ⁰ C and 150 ⁰ C. Particularly, the reaction temperature is between -25°C and 25°C. More particularly, the reaction temperature is about 0 ⁰ C.

In another embodiment, the process of making a compound further includes a purification step of extracting the first compound with water and a water-insoluble solvent from the reaction mixture. Particularly, the water-insoluble solvent is selected from

chloroform, dichloromethane, and dichloroethane. More particularly, the water-insoluble solvent is dichloromethane.

In a further embodiment, the process of making a compound further includes another purification step of purifying the first compound by chromatography such as flash column chromatography using a suitable eluent.

In an even further embodiment, the process of making the compound further comprises a second step of reacting said first compound with a reducing agent to form a compound of formula II

II wherein R ¹ is selected from hydrogen, C^alkyl, C _2-6 alkenyl, halogenated Q-galkyl, C _1-6 alkoxy, -OH, and amino; and n, m, and p are independently selected from O, 1 and 2. In one embodiment, the reducing agent is selected from a sodium or lithium aluminum hydride, sodium borohydride, potassium borohydride, lithium trimethoxy borohydride, lithium cyanoborohydride, sodium triacetoxyborohydride, potassium hydride, calcium hydride, sodium hydride, and hydrogen with Ra-Ni. Particularly, the reducing agent is hydrogen with Ra-Ni and lithium aluminum hydride. In one embodiment, R ¹ of formula II is selected from hydrogen and C _h alky!.

In another embodiment, n, m and p of formula II are 1 and R ¹ is hydrogen. In another embodiment, the second step of the reaction is carried out at a temperature between 0°C and 150 ⁰ C in a polar solvent such as tetrahydrofuran. Particularly, the reaction temperature is between 5O ⁰ C and 100 ⁰ C. More particularly, the reaction temperature is about 75°C.

In another embodiment, the compound of formula II may be further purified using common purification procedures for organic compounds, such as distillation, extraction, and chromatography.

In another embodiment, the compound of formula I may be prepared by a process of reacting a compound of formula III with water and a hydrolysis catalyst,

III wherein R ¹ is selected from hydrogen, Q-βalkyl, C _2-6 alkenyl, halogenated Ci-βalkyl, Ci _-6 alkoxy, -OH, and amino; and n, m, and p are independently selected from 0, 1 and 2.

In a particular embodiment, R ¹ of formula III is selected from hydrogen and C _1-6 alkyl. In a more particular embodiment, n, m and p of formula III are 1 and R ¹ is hydrogen.

In one embodiment, the ethylene acetal orketal (1,3-dioxolane derivative) of formula III may be replaced with other type of ketone protecting group such as those illustrated in T.W. Greene & P.G.M. Wuts, Protective Groups in Organic Synthesis (2nd edition) J. Wiley & Sons, 1991.

In one embodiment, the hydrolysis catalyst is an acid. Particularly, the hydrolysis catalyst is ammonium cerium (IV) nitrate. In another embodiment, the step of reacting a compound of formula III with water may be carried out at a temperature between O ⁰ C and 100 ⁰ C. Particularly, the reaction is carried out at about 7O ⁰ C.

In one embodiment, the compound of formula III may be prepared by a process including: reacting a compound of formula IV with a tosylmethyl isocyanide at a temperature between -25 ⁰ C and 150 ⁰ C,

IV wherein R ¹ is selected from hydrogen, Q-βalkyl, C _2-6 alkenyl, halogenated C^alkyl, Cμβalkoxy, -OH, and amino; and n, m, and p are independently selected from 0, 1 and 2.

In a particular embodiment, R ¹ of formula IV is selected from hydrogen and C _1- βalkyl. In a more particular embodiment, n, m and p of formula IV are 1 and R ¹ is hydrogen.

In a further embodiment, the present invention provides a process of making a compound of formula II including the steps of:

II a) reacting a compound of formula IV with a tosylmethyl isocyanide at a temperature between -25 ⁰ C and 150 ⁰ C to form a compound of formula III,

rv b) reacting a compound of formula III with water and a hydrolysis catalyst to form a compound of formula I,

III c) reacting a compound of formula I with (dialkylamino)sulfur trifluoride to form a compound of formula V,

I d) reacting a compound of formula V with a with a reducing agent to form the compound of formula II,

V wherein R ¹ is selected from hydrogen, C^aUcyl, C2- ₆ alkenyl, halogenated Ci _-6 alkyl, Ci-βalkoxy, -OH, and amino; and n, m, and p are independently selected from 0, 1 and 2.

In a particular embodiment, R ¹ is selected from hydrogen and C _1-6 alkyl. In a more particular embodiment, n, m and p are 1 and R ¹ is hydrogen.

EXAMPLES

l,4-Dioxaspiro[4.5]decane-8-carbonitrile

A solution of t-BuOK (22.8 g, 0.203 mol) in a 1: 1 mixture of t-BuOH and 1,2- dimethoxyethane (200 niL) was added to a solution of 1,4-cyclohexanedione monoethylene ketal (15.5 g, 0.099 mol) and tosylmethyl isocyanide (20.3 g, 0.104 mol) in dimethoxyethane (200 mL) at 0 ⁰ C. The reaction mixture was stirred for one hour at 0 ⁰ C, allowed to warm to ambient temperature and stirred for one extra hour. The reaction mixture was poured in water (500 mL). The product was extracted with hexane (3 x 200 mL) and ether (3 x 200 mL). The combined organics were dried with anhydrous Na ₂ SO ₄ and the solvent was concentrated. The product was purified by flash chromatography on silica gel using EtOAc 40% in hexane as eluent to afford the title compound as a colorless liquid. Yield: 11.5 g (69%). ¹ H NMR (400 MHz, METHANOL-D ₄ ): δ 1.55 - 1.69 (m, 2 H), 1.70 - 1.80 (m, 2 H), 1.78 - 1.90 (m, 2 H), 1.90 - 2.05 (m, 2 H), 2.71 - 2.89 (m, 1 H), 3.86 - 3.98 (m, 4 H).

4-OxocyclohexanecarbonitriIe

A solution of ammonium cerium (IV) nitrate (3.70 g, 6.75 mmol) in water (100 mL) was added to a solution of l,4-dioxaspiro[4.5]decane-8-carbonitrile (11.3 g, 67.5 mmol) in MeCN (200 mL) and water (100 mL) at 70 ⁰ C. The reaction mixture was stirred for 45 minutes at 7O ⁰ C and cooled to ambient temperature where 100 mL of water were added. The product was extracted with ether (4 x 200 mL). The combined organics were

washed with brine and dried over MgSO ₄ . The product was purified by flash chromatography on silica gel using EtOAc 50% in hexane as eluent to afford the title compound as a colorless liquid. Yield: 6.30 g (75%). ¹ H NMR (400 MHz, CHLOROFORM-D): δ 2.07 - 2.31 (m, 4 H), 2.34 - 2.53 (m, 2 H), 2.54 - 2.72 (m, 2 H), 2.95 - 3.14 (m, I H).

4,4-Difluorocyclohexanecarbonitrile

A solution of (Diethylamino)sulfur trifluoride (46.7 g, 289 mmol) in DCM (200 mL) was slowly added to a solution of 4-oxocyclohexanecarbonitrile (32.4 g, 263 mmol) in DCM (400 mL) at 0°C. The reaction mixture was stirred for 2 hrs. and quenched with water (100 mL). The organic layer was separated and dried with anhydrous MgSO ₄ . The solvent was concentrated to provide a 7:3 mixture of 4,4-Difluorocyclohexanecarbonitrile and 4-fluorocyclohex-3-ene-l-carbonitrile. MCPBA 77% (45 g, 200 mmol) was stirred in CHCl ₃ (600 mL) for 30 min. The solution was dried with anhydrous Na ₂ SO ₄ and filtred. The 7:3 mixture of 4,4-Difluorocyclohexanecarbonitrile and 4-fluorocyclohex-3-ene-l- carbonitrile was added to the resulting MCPBA solution and stirred at ambient temperature for 18 hrs. The reaction mixture was washed with NaOH 1.5 M (3 x 300 mL) and dried with anhydrous MgSO ₄ . The solvent was concentrated and the residue was distilled under reduced pressure to provide the pure title compound as a colorless liquid. Yield 18.2 g (47%): IHNMR (400 MHz, CHLOROFORM) δ 1.86-1.96 (m, 1 H), 1.95-2.03 (m, 5 H), 2.03-2.22 (m, 2 H), 2.68-2.85 (m, 1 H).

[(4,4-Difluorocyclohexyl)methyI]amine

LiAlH ₄ (2.20 g, 57.9 mmol) was added to a solution of 4,4- difluorocyclohexanecarbonitrile (6.10 g, 42.0 mmol) in THF (250 mL) at ambient temperature. The reaction mixture was refluxed to 75°C and stirred for four hours. The reaction mixture was cooled to 0 ⁰ C and slowly quench by addition of MeOH over 1 hour. The mixture was filtered over a Celite pad and the filtrate was concentrated. The product was purified by distillation (65°C/15 mmHg) to afford the title compound as a colorless liquid. Yield: 2.55 g (40%). ¹ H NMR (400 MHz, CHLOROFORM-D): δ 1.17 - 1.46 (m, 3 H), 1.52 - 1.94 (m, 2 H), 2.03 - 2.32 (m, 2 H), 2.57 - 2.70 (m, 2 H).

[(4,4-Difluorocyclohexyl)methyl]amine

Raney® 2800 nickel, slurry in water, active catalyst (6 mL) was added to a solution of 4,4-difluorocyclohexanecarbonitrile (18.2 g, 125 mmol) in EtOH (300 mL). The reaction mixture was shaken overnight in a Parr® hydrogenation apparatus under a 50 PSI atmosphere of hygrogen. The reaction mixture was filtered over a celite pad and the solvent was concentrated to provide the title compound as a colorless liquid. Yield 16 g (87%). ¹ H NMR (400 MHz, CHLOROFORM-D): δ 1.17 - 1.46 (m, 3 H), 1.52 - 1.94 (m, 2 H), 2.03 - 2.32 (m, 2 H), 2.57 - 2.70 (m, 2 H).