A process for preparing trisubstituted phenyl derivatives comprising

a (1 H-1 ,2,4-triazol-1 -yl)alkyl group Field of the invention

The present invention relates in general to the field of organic chemistry, and in particular to the preparation of phenyl derivatives comprising a (1 H-1 ,2,4-triazol-1-yl)alkyl group such as anastrozole (2,2'-(5-((1 H-1 ,2,4-triazol-1 -yl)methyl)-1 ,3-phenylene)

bis(2-methyl-propanenitrile).

Background of the invention

Compounds belonging to the group of phenyl derivatives comprising a (1 H-1 ,2,4-triazol-1 - yl)alkyl group may represent valuable nonsteroidal aromatase inhibitors. For example, anastrozole (2,2'-(5-((1 H-1 ,2,4-triazoM -yl)methyl)-1 ,3-phenylene)

bis(2-methyl-propanenitrile) is in use for treatment of estrogen dependent breast cancer.

EP 0 296 749 A1 discloses (substituted aralkyl)heterocyclic compounds, among others a deuterated anastrozole derivative prepared by two different pathways. In both pathways, the last reaction step is reacting the sodium sodium salt of 1 ,2,4-triazole with 1- chlorodideuteriomethyl-3,5-bis(2-cyanoisopropyl)toluene. Neither yield nor purity of the product is given. WO 2005/105762 A1 discloses the preparation of anastrazol wherein 1 -bromomethyl-3,5- bis(2-cyanoisopropyl)toluene is reacted with the sodium salt of 1 ,2,4-triazole. Thereby it was found that the isomer (2,2'-(5-((1 H-1 ,3,5-triazol-1 -yl)methyl)-1 ,3-phenylene) bis(2-methyl-propanenitrile), also called isoanastrozol, is formed as an undesired by-product. Said isoanastrozole was present in anastrazol even after repeated purification by crystallization in an amount of more than 0.5% determined by HPLC. Furthermore, it was found that the content of isoanastrozole impurity can be significantly reduced to below 0.1 % level by purification in form of anastrozole acid addition salts, however, overall yield was quite low. In Ge, Zemei; Cui, Jialing; Cheng, Tieming; Li, Runtao; Chinese Journal of Medicinal

Chemistry, (2003) Vol. 13, No. 3, 146-147, preparation of anastrozole via N-alkylation of 1 ,2,4-triazole with 1 -bromomethyl-3,5-bis(2-cyanoisopropyl)toluene by phase transfer catalysis is reported, wherein xylene is used as the solvent, K ₂ C0 ₃ /KOH is used as the base, and tetra-n-butylammonium bromide (TBAB) is used as the phase transfer catalyst, and reaction was carried out under reflux conditions. However, this phase transfer catalysis requires harsh reaction conditions in view of reaction temperature and reaction times. The product was purified by repeated re-crystallisations, however there is no information concerning purity detected by HPLC.

WO 2006/108155 A1 describes a process for preparing anastrozole via N-alkylation of 1 ,2,4-triazole with 1-bromomethyl-3,5-bis(2-cyanoisopropyl)toluene in the presence of a base selected from the group consisting of NaOH, KOH, K ₂ C0 ₃ and Na ₂ C0 ₃ at

temperatures below -20°C. The resulting crude product is purified by aqueous extraction operations, filtration and re-crystallisation, wherein the impurity profile of anastrozole is not more than about 0.16% area by HPLC of isoanastrozole, not more than about 0.14% area by HPLC of 3,5-bis(2-cyanoisopropyl)toluene, and not more than about 0.18% area by HPLC of other impurities.

WO 2007/002722 A1 also discloses a process for preparing anastrozole via N-alkylation of 1 ,2,4-triazole with 1-bromomethyl-3,5-bis(2-cyanoisopropyl)toluene in the presence of NaOH at temperatures below -20°C, wherein the product has a purity of 99.94% area by HPLC and 0.06% area by HPLC of an impurity other than isoanastrozole. The low reaction temperatures of the processes of WO 2006/108155 A1 and WO 2007/002722 A1 are disadvantageous for industrial application.

WO 2007/039913 discloses a process for preparing anastrozole wherein

1-halogenomethyl-3,5-bis(2-cyanoisopropyl)toluene is reacted with the potassium or sodium salt of 1 ,2,4-triazole. The purity of the product is 99.9% area by HPLC after purification comprising aqueous work up operations, column chromatography and recrystallisation.

US 2007/0100148 discloses a process for preparing anastrozole wherein 1-bromomethyl- 3,5-bis(2-cyanoisopropyl)toluene is reacted with the sodium salt of 1 ,2,4-triazole. The product is purified by aqueous work-up, filtration over silica gel and recrystallisation. While the thus obtained anastrozole has a puritity of 99.97% by HPLC, yields are quite low.

DE 10 2005 037 484 A1 discloses a process for preparing anastrozole via N-alkylation of 1 ,2,4-triazole with 1-bromomethyl-3,5-bis(2-cyanoisopropyl)toluene. Purification of the crude product is effected by multiple purification steps, wherein formation of an anastrozole acid addition salt is the key step. Purity of anastrozole obtained by said process is 99.5% by HPLC, while yields are quite low. Therefore, the object of the present invention is to provide an improved process for preparing phenyl derivatives comprising a (1 H-1 ,2,4-triazol-1-yl)alkyl group such as anastrozole (2,2'-(5-((1 H-1 ,2,4-triazol-1 -yl)methyl)-1 ,3-phenylene)

bis(2-methyl-propanenitrile).

Summary of the invention

Various aspects, advantageous features and preferred embodiments of the present invention as summarized in the following items, respectively alone or in combination, contribute to solving the object of the invention:

A process for preparing a compound of formula II

wherein and R ₂ independently from each other represent

substituted or unsubstituted alkyl, substituted or unsubstituted aryl or substituted or unsubstituted alkylaryl,

X is a substituted or unsubstituted alkylene group wherein a compound of formula I

wherein and R ₂ and X are defined as above and wherein Z is a leaving group, is reacted with 1 ,2,4-triazole in the presence of a polyethylene glycol (PEG) phase transfer catalyst.

The term "alkyl" as used herein typically includes straight, branched or cyclic CTC ₁₂ hydrocarbons, preferably Ci-C ₈ hydrocarbons.

The term "aryl" as used herein typically refers to C ₆ -C ₁₄ monocyclic or bicyclic hydrocarbon aromatic rings wherein 1 to 3 carbon atoms are exchanged by oxygen, nitrogen or sulfur, preferably C ₆ -Ci ₀ monocyclic or bicyclic hydrocarbon aromatic rings such as phenyl or naphtyl.

The term "arylalkyl" as used herein typically means that the aforementioned aryl moieties are incorporated into the aforementioned straight or branched alkyl moieties either at one of the proximal or distal ends of the alkyl chain or between the aforementioned alkyl chains. Proximal end means the portion of P^ and R ₂ adjacent to the benzene moiety of compound of formula I, while distal means the terminal end of the arylalkyl moiety.

The term "alkylene" as used herein typically includes straight, branched or cyclic C C ₁₂ hydrocarbons, preferably C^-C ₈ hydrocarbons.

The term "substituted" as used herein typically means that the aforementioned alkyl, aryl, arylalkyl and alkylene moieties are substituted with functional group(s) which do(es) not adversely affect N-alkylation reaction of the process according to item 1 . For example, the functional group(s) may be selected from the group consisting of nitro, cyano, -CO-OR ₃ , -CS-OR ₃ , -S0 ₂ -OR ₃ , -CO-R ₃ , -CS-R ₃ , -S0 ₂ -R ₃ , -0-R ₃ , -S-R ₃ wherein R ₃ is .substituted or unsubstituted alkyl, substituted or unsubstituted aryl or substituted or unsubstituted alkylaryl, and the meaning of "alkyl", "aryl" and "alkylaryl" are defined as above.

The term "phase transfer catalyst" as used herein means a catalyst providing for migration or movement of a reactant in a heterologous system from one phase into another phase where reaction can take place. For example, the phase transfer catalyst may provide for migration or movement of a base which is in solid or substantially solid state in the reaction mixture, into the liquid phase of the reaction mixture.

The term "leaving group" is a term commonly used in the art to mean any atom or group of atoms that can depart; typically the leaving group departs with a pair of electrons in a heterolytic bond cleavage that is in the form of anions or neutral molecules during a substitution or displacement reaction. The leaving group may be selected from, without being limited to, halides, such as iodide, bromide and chloride; sulfonates, such as triflates, fluorosulfonates, tosylates, besylates, mesylates; and the like. A preferred leaving group Z is CI, Br or I.

The procedural concept according to this aspect of the invention involving conversion of a compound of formula I to a compound of formula II provides for an industrially applicable, robust and competitive process. By applying a polyethylene glycol (PEG) phase transfer catalyst, surprisingly mild reaction conditions can be used in a beneficial manner, and reaction times can be significantly shortened, while the product can be obtained in exceptionally high yields. Moreover, the amount of undesired by-products or degradation products is effectively reduced or can be minimized, which in turn provides for significantly simplified purification of the compound of formula II, yielding a highly pure product.

(2) A process for preparing a compound of formula II

wherein and R ₂ independently from each other represent

substituted or unsubstituted alkyl, substituted or unsubstituted aryl or substituted or unsubstituted alkylaryl,

X is a substituted or unsubstituted alkylene group, wherein a compound of formula I

wherein and R ₂ and X are as defined above and Z is a leaving group, is reacted with 1 ,2,4-triazole in a solvent allowing precipitation of a compound of formula III

, wherein and R ₂ and X are as defined above and wherein the compound of formula III can be separated from the reaction mixture.

The reaction can be terminated when conversion to the desired compound is substantially complete. Preferably, conversion is controlled by suitable means, for example by thin layer chromatography.

According to this technical solution of the object of the invention, which may be used alternative to, or concurrent with, the technical solution of item (1 ) above by selecting a solvent allowing precipitation of compound of formula III, while preferably maintaining the compound of formula II in solution with the solvent, isolation and purification of compound of formula II is significantly simplified by removing the undesired by-product of compound of formula III from the reaction mixture (which has precipitated from the selected solvent), preferably at the end of the reaction. This favours industrial application by providing a robust and competitive process, as well as simplified purification of compound of formula II, while significantly contributing to high yield purity. If desired, a "one pot" concept is made possible since all work-up steps can be easily carried out by, for example, extraction and/or filtration in order to remove undesired by-products, while no laborious chromatography or other purification step is necessary which would have to be carried out outside a reaction system. Compounds of formula II, in particular anastrozole, represent hazardous compounds. Anastrozole is an aromatase inhibitor generally classified as substance of category 4, and for handling such substances, special care has to be taken during industrial manufacturing, particularly regarding health, safety and environmental issues. Thus, the present "one pot" concept contributes to an industrially applicable and competitive process, whilst significantly improving working conditions such that legal, health,

environmental and safety (HSE) issues are taken into account. The process according to item (1 ) or (2), wherein and R ₂ independently from each other represent substituted or unsubstituted alkyl, preferably C!-C ₁₂ alkyl, more preferably C C ₆ alkyl, even more preferably C ₃ -C ₆ alkyl, yet even more preferably propyl, in particular isopropyl.

The process according to any one of the preceding items, wherein R^ and R ₂ are isopropyl substituted in 2-position.

The process according to item (3) or (4), wherein RT and R ₂ are independently from each other substituted with at least one functional group selected from the group consisting of nitro, cyano, -CO-OR ₃ , -CS-OR ₃ , -S0 ₂ -OR ₃ , -CO-R ₃ , -CS-R ₃ , -S0 ₂ -R ₃ , -0-R ₃ , -S-R ₃ , wherein R ₃ is substituted or unsubstituted alkyl, substituted or unsubstituted aryl or substituted or unsubstituted alkylaryl; preferably cyano, -CO- OR ₃ , -CO-R ₃ , -0-R ₃ ; more preferably cyano.

The process according to item (5), wherein R^ and R ₂ are substituted with one functional group respectively.

The process according to any one of the preceding items, wherein Ri and R ₂ are the same.

The process according to any one of the preceding items, wherein X is C1-C12 alkylene, preferably d-C ₈ alkylene, more preferably Ci-C ₆ alkylene, even more preferably C^C^ alkylene, in particular methylene.

The process according to any one of the preceding items, wherein both R^ and R ₂ represent isopropyl substituted in 2-position with cyano, and X is methylene.

The process according to any one of the preceding items, wherein Z is selected from the group consisting of halides and sulfonates, preferably Z is selected from CI, Br or I , triflates, fluorosulfonates, tosylates, besylates and mesylates, most preferred Z is Br.

The process according to any one of the preceding items, wherein R^ and R ₂ are located at the 3-position and 5-position of the benzene ring of compound of formula I respectively. (12) The process according to item (1 ) and further items dependent thereon, wherein the reaction is carried out in a solvent selected from the group of polar protic solvents, the group of polar aprotic solvents and the group of non polar aprotic solvents, preferably linear or branched alcohols, carboxylic acid alkyl esters, linear or cyclic alkyl ethers, alkyl nitriles, alkyl halides, ketones, Ν,Ν-dialkyl carboxylic acid amides, dialkyl sulfoxides, alkanes, alkenes, substituted or unsubstituted aromatic hydrocarbons, perhalogenated hydrocarbons, more preferably linear or branched d-d-alcohols, CrC ₄ -carboxylic acid-C ₁ -C ₄ -alkyl esters, linear C -C ₄ -dialkyl ethers or cyclic ethers wherein at least one C ₃ -C ₇ -linear alkyl residue cooperatively with at least one oxygen atom form(s) a ring, C -C ₄ -alkyl nitriles, Ci-C ₄ -alkyl halides, d-d- ketones, N,N-d-C ₄ -dialkyl d-C ₄ -carboxylic acid amide, C ₁ -C ₄ -dialkyl sulfoxides, C ₅ - do-alkanes, C ₅ -Ci ₀ -alkenes, substituted or unsubstituted C ₆ -Ci ₂ -aromatic hydrocarbons, d-d-perhalogenated hydrocarbons, even more preferably i- propanol ,n-butanol, dimethylformamide, substituted or unsubstituted C ₆ -do- aromatic hydrocarbons, dimethyl sulfoxide, THF, MTBE, ethyl acetate, methylene chloride or acetone, yet even more preferably i-propanol ,n-butanol,

dimethylformamide, substituted or unsubstituted C ₆ -Ci ₀ -aromatic hydrocarbons, most preferably C ₆ -C ₁₀ -aromatic hydrocarbons, and in particular toluene.

(13) The process according to item (2), wherein the solvent allowing precipitation of compound of formula III is selected from aromatic hydrocarbons, ethers and solvent mixtures thereof, provided that said selected solvent precipitates the compound of formula III.

(14) The process according to any one of preceding items, wherein the reaction is

carried out in toluene, methyl tert. -butyl ether (MTBE), or a mixture of the solvents with each other or with other solvents.

According to the preferred embodiments of above items, the formation of compound of formula III

representing an undesired by-product can be substantially reduced, such that exceptionally high yields of the compound of formula II are obtained and purification of the compound of formula II is considerably simplified.

A process for preparing a compound of formula II'

, wherein a compound of formula Γ

is reacted with 1 ,2,4-triazole in toluene as a solvent.

The reaction can be terminated when conversion to the desired compound is substantially complete. Preferably, conversion is controlled by suitable means, for example by thin layer chromatography. In accordance with this preferred embodiment of this aspect, a concurrently formed compound of formula III'

is separated from the reaction mixture, preferably after termination of the reaction. Concerning the description of leaving group Z, reference is made to the description in item (1 ) and (10) above.

According to this aspect of the invention, by selecting toluene as a particularly suitable solvent, the formation of the compound of formula III' is effectively reduced or minimized during the reaction or is easily removed after its precipitation, which provides for both substantially enhanced yields and exceptional purity of the compound of formula II'. In addition, purification of the compound of formula ΙΓ can be markedly simplified by removing the undesired by-product of the compound of formula III' at the end of the reaction. Thus, a "one pot" concept is made possible since all work-up steps can be easily carried out by extraction and/or filtration in order to remove undesired by-products, while no laborious chromatography or other purification step is necessary which would have to be carried outside the reaction vessel. Reference is made to the explanations above regarding HSE constraints of the compound of formula ΙΓ, representing anastrozole.

The process according to any one of items (2) to (15), wherein the compound of formula III or III' is removed from the reaction mixture at the end of the reaction by filtration.

The process according to any one of items (2) to (16), wherein the reaction is carried out in the presence of a phase transfer catalyst, preferably said phase transfer catalyst is selected from the group of polyethylene glycols, tetraalkyl ammonium salts and tetraalkyl phosphonium salts, more preferably said phase transfer catalyst is selected from the group of polyethylene glycols and tetraalkyl ammonium salts, and in particular said phase transfer catalyst is a polyethylene glycol. The process according to item (1) or (17), wherein the polyethylene glycol phase transfer catalyst is a polyethylene glycol (PEG) phase transfer catalyst having an average molecular weight of about 200 to 800 g/mol, preferably about 300 to 700 g/mol; more preferably about 400 to 600 g/mol; even more preferably, the PEG transfer catalyst is PEG 400 or PEG 600, in particular PEG 600.

The process according to item (17) or (18), wherein the phase transfer catalyst is used in about 0.01 to 0.5 times molar amounts, preferably 0.03 to 0.1 times molar amounts, more preferably 0.04 to 0.09 times molar amounts, and in particular 0.06 to 0.08 times molar amounts relative to compound of formula I.

The process according to any one of the preceding items, wherein said reaction is carried out in the presence of a base selected from the group consisting of linear or branched alkoxides; hydroxides, carbonates or hydrogencarbonates of alkaline metals or alkaline earth metals; preferably KOH, NaOH, NaHC0 ₃ , Na ₂ C0 ₃ , KHC0 ₃ , K ₂ C0 ₃ , KO-tert-butyl; more preferably KOH, K ₂ C0 ₃ , KO-tert-butyl; in particular K ₂ C0 ₃ .

The process according to any one of the preceding items, wherein the compound of formula I or , dissolved in a solvent according to item (12), (13) or (14), is added continuously to a stirred mixture comprising 1 ,2,4-triazole or a salt thereof, a base according to item (19) and a solvent according to item (12).

The process according to item (21), wherein the addition is carried out continuously over a period of about 5 to 240 min, preferably over a period of about 5 to 120 min.

The process according to any one of the preceding items, wherein the reaction is carried out at a temperature of about 20 to 120°C, preferably 40 to 50°C, more preferably 40 to 45°C.

The process according to any one of the preceding items, wherein the reaction is carried out for a time of 0.5 to 12 h, preferably 2.5 to 10 h, more preferably 2.7 to 6.5 h, and in particular 2.8 to 5 h. (25) The process according to item (1) or (2), wherein the compound of formula I or Γ is added to a solution comprising 1 ,2,4-triazole or a salt thereof over a period of about 5 to 240 min, preferably over a period of about 5 to 120 min, the reaction being carried out for a time of 0.5 to 12 h, preferably of 2.5 to 10 h, at a temperature of about 20 to 120°C, preferably 40 to 50°C.

The process according to any one of the preceding items, wherein the ratio of the volume of the solvent employed in said process to the mass of the compound of formula I or I' employed in said process is in a range of 2: 1 to 15: 1 , preferably 3: 1 to 12: 1 , more preferably 5:1 to 1 1 : 1 , even more preferably 7: 1 to 10: 1 , and in particular 9: 1 to 10: 1. (27) The process according to any one of the preceding items, wherein the PEG phase transfer catalyst is used in about 0.01 to 0.5 times molar amounts, preferably 0.03 to 0.1 times molar amounts, more preferably 0.04 to 0.09 times molar amounts, and in particular 0.06 to 0.08 times molar amounts relative to the compound of formula I. (28) The process according to any one of the preceding items, further comprising a step of forming an acid addition salt of the compound of formula II or of formula II', preferably an HCI addition salt.

The process according to any one of the preceding items, further comprising a step of crystallising or recrystallising the compound of formula II or formula ΙΓ or its acid addition salt from a suitable solvent.

(30) The process according to item (29), wherein the compound of formula II or formula ΙΓ or its acid addition salt is recrystallised from a solvent comprising or consisting of toluene or isopropanol.

(31 ) The process according to any one of the preceding items, wherein the compound of formula II or ΙΓ or its acid addition salt has a purity of higher than 99.7, such as up to 99.95%, measured by HPLC.

(32) A process for producing a pharmaceutical composition, comprising the steps of:

i) preparing a compound of formula II or I Γ or its acid addition salt according to any one of items (1 ) to (31 ), and

ii) mixing said compound of formula II or II' or its acid addition salt with at least one pharmaceutically-acceptable excipient. The term "pharmaceutical composition" as used herein means a formulation comprising a safe and effective amount of active agent and pharmaceutically- acceptable excipients.

The term "pharmaceutically acceptable excipient" as used herein means any physiologically inert, pharmacologically inactive material known in the art being compatible with the physical and chemical characteristics of the active agent.

Detailed description of the Invention

The present invention is now described in more detail by referring to further preferred and further advantageous embodiments and examples, which are however presented for illustrative purposes only and shall not be understood as limiting the scope of the present invention.

In order to improve a process for the preparation of a compound of formula II (phenyl derivatives comprising a (1 H-1 ,2,4-triazol-1 -yl)alkyl group) and a compound of formula II' (anastrozole, that is 2,2'-(5-((1 H-1 ,2,4-triazol-1 -yl)methyl)-1 ,3-phenylene)bis(2-methyl- propanenitrile), extensive test series were carried out by the inventors to find critical factors that are particularly suited to increase product yields and to decrease the number and compound of formula I', wherein Z represents amount of by-products, while significantly simplifying preparation due to beneficial reaction conditions and/or less necessary purification steps. The compound of formula II' (anastrozole, that is 2,2'-(5-((1 H-1 ,2,4-triazol-1 -yl)methyl)-1 ,3- phenylene)bis(2-methyl-propanenitrile) may be prepared via N-alkylation of 1 ,2,4 triazole with the a leavin group as described above:

However, in such conventional processes for preparing anastrozole, an isomer compound of formula III', the so-called isoanastrozole, is formed in relatively large amounts. In conventional processes, removal of the compound of formula III' from the crude product of the compound of formula Ι is difficult and affords one or multiple laborious subsequent purification step(s), wherein the yield of anastrozole is significantly decreased by said purification step(s). Furthermore, a drawback of some prior art processes is that they require harsh and/or industrially not applicable reaction conditions. According to sent invention, a compound of formula II

wherein Ri and R ₂ independently from each other represent

substituted or unsubstituted alkyl, substituted or unsubstituted aryl or substituted or unsubstituted alkylaryl, and X is a substituted or unsubstituted alkylene group,

is prepared by a process wherein a compound of formula I

wherein F and F are defined as above,

and wherein Z is a leaving group,

is reacted with 1 ,2,4-triazole in the presence of a polyethylene glycol (PEG) phase transfer catalyst.

The above mentioned aspect provides a process for preparing a compound of formula II in exceptionally high yields. In addition, the process can be carried out at mild reaction conditions, that is at moderate reaction temperatures in combination with significantly shortened reaction times. Due to the mild reaction conditions, formation of undesired byproducts or degradation products is effectively prevented. Thus, the process provides for a significantly simplified purification of the compound of formula II, yielding a highly pure product. According to invention, a compound of formula II

wherein and R ₂ independently from each other represent

substituted or unsubstituted alkyl, substituted or unsubstituted aryl or substituted or unsubstituted alkylaryl, and X is a substituted or unsubstituted alkylene group,

is prepared by a process wherein a compound of formula I

wherein and R ₂ are defined as above, and wherein Z is a leaving group,

is reac -triazole in a solvent allowing precipitation of a compound of formula III

wherein the compound of formula ill can be separated from the reaction mixture, preferably after termination of the reaction.

It was surprisingly found that this aspect of the invention provides for significantly simplified isolation and purification of the compound of formula II. As a solvent is selected to allow precipitation of the isomer compound of formula III, while preferably maintaining the compound of formula II in solution with the solvent, the undesired by-product compound of formula III can be simply removed at the end of the reaction. Thereby, a "one pot" concept is rendered possible, since all work-up steps can be easily carried out, for example by extraction and/or filtration in order to remove undesired by-products - no laborious chromatography or other purification step is necessary which would have to be carried out outside a reaction system. Compounds of formula II may also represent hazardous compounds. Therefore, the present "one pot" concept contributes to an industrially applicable and competitive process, while working conditions are significantly improved such that legal, health, environmental and safety (HSE) issues are taken into account.

According to yet another aspect of the invention, a compound of formula ΙΓ

is prepared by a process wherein a compound of formula I'

wherein Z is a leaving group,

is reacted with 1 ,2,4-triazole in toluene as a solvent. In this embodiment, the process is performed such that the compound of formula III'

Γ ^ N is removed from the reaction mixture, preferably after termination of the reaction, and preferably by filtration.

It was found feasible to yield a highly pure compound of formula ΙΓ by selecting toluene as the solvent for the reaction in order to effectively reduce or prevent the formation of the compound of formula III' during the reaction. Thereby, the compound of formula ΙΓ is obtained in both enhanced yields and exceptional purity. Furthermore, this aspect of the invention also renders possible the aforementioned "one pot" concept. The compound of formula Γ is readily available. For example, it can be prepared as described in WO 2005/105762 A1 .

According to a preferred embodiment, the undesired isomer compound of formula III or III' is removed from the reaction mixture at the end of the reaction by filtration.

Preferably, the reaction is carried out in the presence of a phase transfer catalyst, preferably said phase transfer catalyst is selected from the group of polyethylene glycols, tetraalkyl ammonium salts and tetraalkyl phosphonium salts, more preferably said phase transfer catalyst is selected from the group of polyethylene glycols and tetraalkyl ammonium salts, and in particular said phase transfer catalyst is a polyethylene glycol.

It was surprisingly found that carrying out the conversion of compound of formula I' into the compound of formula II' in the presence of a polyethylene glycol (PEG) phase transfer catalyst provides for both mild reaction conditions and high yields. Preferably, the PEG phase transfer catalyst has an average molecular weight of about 200 to 800 g/mol, more preferably about 300 to 700 g/mol; even more preferably about 400 to 600 g/mol; yet even more preferably, the PEG transfer catalyst is PEG 400 or PEG 600, in particular PEG 600. Furthermore, the PEG phase transfer catalyst is suitably used in about 0.01 to 0.5 times molar amounts, preferably 0.03 to 0.1 times molar amounts, more preferably 0.04 to 0.09 times molar amounts, and in particular 0.06 to 0.08 times molar amounts relative to the compound of formula I. Thus, a stable and reliable process is provided. The amount of catalyst relative to the compound of formula I is suitably selected such that the reaction can be smoothly accomplished under mild conditions, while the content of isomer III or III' is surprisingly reduced in an effective manner.

According to another preferred embodiment, a process according to any one of the aforementioned aspects of the invention is carried out in a solvent selected from the group of polar protic solvents; polar aprotic solvents; and non polar aprotic solvents, preferably linear or branched alcohols, carboxylic acid alkyl esters, linear or cyclic alkyl ethers, alkyl nitriles, alkyl halides, ketones, Ν,Ν-dialkyl carboxylic acid amides, dialkyl sulfoxides, alkanes, alkenes, substituted or unsubstituted aromatic hydrocarbons, perhalogenated hydrocarbons, more preferably linear or branched C C ₄ -alcohols, C^C^carboxylic acid-Ci- C ₄ -alkyl esters, linear C ₁ -C ₄ -dialkyl ethers or cyclic ethers wherein at least one C ₃ -C ₇ -linear alkyl residue cooperatively with at least one oxygen atom form(s) a ring, C ₁ -C ₄ -alkyl nitriles, C ₁ -C ₄ -alkyl halides, CrC-ketones, N,N-C ₁ -C ₄ -dialkyl C ₁ -C ₄ -carboxylic acid amide, C ₁ -C4- dialkyl sulfoxides, C ₅ -C ₀ -alkanes, C ₅ -C ₀ -alkenes, substituted or unsubstituted C ₆ -Ci ₂ - aromatic hydrocarbons, CVC^-perhalogenated hydrocarbons, even more preferably i-propanol, n-butanol, dimethylformamide, substituted or unsubstituted C ₆ -Ci ₀ -aromatic hydrocarbons, dimethyl sulfoxide, THF, MTBE, ethyl acetate, methylene chloride or acetone, yet even more preferably i-propanol , n-butanol, dimethylformamide, substituted or unsubstituted C ₆ -C ₁₀ -aromatic hydrocarbons, most preferably C ₆ -C ₁₀ -aromatic

hydrocarbons, and in particular toluene.

The c ompound of formula III

representing an undesired by-product can be substantially reduced, wherein

exceptionallyhigh yields of the compound of formula II are obtained and purification of the compound of formula II is considerably simplified. This can be further enhanced when the reaction is carried out in a solvent further chosen to allow precipitation of compound of formula II I. Such a preferred solvent is particularly selected from aromatic hydrocarbons, ethers and solvent mixtures of these solvents with each other or with other solvents, provided that said selected solvent precipitates the compound of formula III. To this end, in the process according to this preferred embodiment the reaction is preferably carried out in toluene, methyl tert.-butyl ether (MTBE) or a mixture thereof.

Furthermore, it was surprisingly found that the residual amount of the isomer compound of formula III can be significantly reduced by suitably setting the ratio of the volume of the solvent employed in said process to the mass of the compound of formula I or Γ employed in said process. Therefore, the ratio of the volume of the solvent employed in said process to the mass of the compound of formula I or I' employed in said process is preferably set within in a range of 2: 1 to 15: 1 , preferably 3: 1 to 12: 1 , more preferably 5:1 to 1 1 : 1 , even more preferably 7: 1 to 10:1 , and in particular 9: 1 to 10: 1.

Preferably, the aforementioned processes are carried out in the presence of a base selected from the group consisting of linear or branched alkoxides; hydroxides, carbonates or hydrogencarbonates of alkaline metals or alkaline earth metals; preferably KOH, NaOH, NaHC0 ₃ , Na ₂ C0 ₃ , KHC0 ₃ , K ₂ C0 ₃ , KO-tert-butyl; more preferably KOH, K ₂ C0 ₃ , KO-tert- butyl; in particular K ₂ C0 ₃ .

According to a further preferred embodiment, in the aforementioned processes, the compound of formula I or I' dissolved in one of the aforementioned solvents is added continuously to a stirred mixture comprising 1 ,2,4-triazole or a salt thereof, one of the aforementioned bases and one of the aforementioned solvents. Preferably, said addition is carried out continuously over a period of about 5 to 240 min, preferably over a period of about 5 to 120 min.

According to a still further preferred embodiment, the aforementioned processes are carried out under at least one condition selected from:

a) the reaction is carried out at a temperature of about 20 to 120°C, preferably

40 to 50°C, more preferably 40 to 45°C;

b) the reaction is carried out for a time of 0.5 to 12 h, preferably 2.5 to 10 h, more preferably 2.7 to 6.5 h, and in particular 2.8 to 5 h.. According to another aspect of the invention, a process for producing a pharmaceutical composition comprises the steps of:

i) preparing a compound of formula II or II' according to any one of preceding items (1 ) to (30) or a pharmaceutically acceptable salt thereof, and ii) mixing said compound of formula II or II' with at least one pharmaceutically- acceptable excipient.

Pharmaceutically-acceptable excipients include, but are not limited to, solvents, polymers, plasticizers, fillers, binders, buffer systems, surfactants, dyes or pigments, preservatives and flavouring agents.

According to a preferred embodiment of the invention, a compound of formula II or II' produced by the aforementioned processes is purified by applying at least one of the following steps: a) washing the combined filtrates obtained from the process with water, b) converting compound of formula II or II' into its respective acid addition salt, c) washing an aqueous phase comprising the aforementioned acid addition salt with an organic solvent,

d) converting the acid addition salt of compound of formula II or II' into compound of formula II or II' in free form,

e) washing the organic phase comprising compound of formula II or II' with water, preferably said organic phase is filtered in a subsequent step,

f) treating the organic phase with a discolorating agent,

9) crystallizing compound of formula II or II'.

According to a further preferred embodiment of the invention, steps a) to g) are

subsequently carried out. In step a), a filter residue is washed with a solvent according to preceding item (12), wherein the filtrate from the reaction mixture and the washing solvent are combined, representing combined filtrates which are washed with water.

Then, in step b), a compound of formula II or II', present in said combined filtrates, is converted to its respective acid addition salt by adding an acid. Preferably, said acid is an organic or inorganic acid, more preferably oxalic acid, hydrochloric acid, hydrobromic acid, even more preferably hydrochloric acid or hydrobromic acid, in particular hydrochloric acid.

Furthermore, preferably said acid is added in concentrated form or in the form of a diluted aqueous solution, preferably in the form of a diluted aqueous solution, more preferably in the form of a diluted aqueous solution having a normality in a range of about 0.05 N to 10

N, even more preferably about 0.4 N to 5 N, yet even more preferably about 0.8 N to 3N, and in particular 1 N.

In step c), an aqueous phase comprising the resulting acid addition salt of the compound of formula II or ΙΓ is separated from the organic phase, and the aqueous phase is washed with a nonpolar aprotic solvent. Preferably, said nonpolar aprotic solvent is selected from the group of alkanes, alkenes, aromatic hydrocarbons, perhalogenated hydrocarbons, more preferably linear or cyclic alkanes, even more preferably cyclic alkanes, yet even more preferably cyclopentane or cyclohexane, in particular cyclohexane.

Next, in step d), the acid addition salt of the compound of formula II or II' is converted into the compound of formula II by adding a base to the aqueous solution, preferably by adding an inorganic base, more preferably an alkaline metal hydroxide or an alkaline earth metal hydroxide, even more preferably an alkaline metal hydroxide, yet even more preferably NaOH or KOH. Said base is added in concentrated form or in form of a diluted aqueous solution, preferably in the form of a diluted aqueous solution more preferably in the form of a diluted aqueous solution having a normality in a range of about 0.05 N to 10 N, even more preferably about 0.4 N to 5 N, yet even more preferably about 0.8 N to 3N, and in particular 1 N.

In step e), an organic solvent is added prior to or subsequent to addition of the base to the aqueous solution, preferably said solvent is selected from the group consisting of nonpolar aprotic solvents, more preferably from the group consisting of alkanes, alkenes, aromatic hydrocarbons, perhalogenated hydrocarbons, preferably aromatic hydrocarbons or linear or cyclic alkanes, more preferably aromatic hydrocarbons, in particular toluene. Preferably, the organic solvent in which the compound of formula II is dissolved is separated from the aqueous phase and washed with water. More preferably, the resulting organic phase is evaporated and the resulting residue is taken up in a polar aprotic solvent, preferably selected from the group of carbon acid esters, more preferably ethyl acetate, wherein the resulting solution or suspension is stirred in the presence of a filter aid, wherein the solution or suspension is filtered over a bed of said filter aid. Preferably, said filter aid is selected from the group consisting of cellulose filter aid, kieselguhr and silica gel, preferably silica gel. Furthermore, preferably the resulting suspension is stirred at ambient temperature, preferably 10 to 35°C, more preferably 15-25°C.

In step f), an organic phase comprising the compound of formula II or ΙΓ, preferably an organic phase obtained from the above described step e), is evaporated and the residue is taken up in a polar protic solvent, preferably linear or branched Ci-C alcohols, more preferably 2-propanol, and a discoloration agent is added to the solution or suspension, wherein the resulting mixture is stirred for a predetermined time at a predetermined temperature, and then filtered at the predetermined temperature. Preferably, said discoloration agent is charcoal, preferably activated charcoal. Furthermore, said

predetermined temperature is within a range of 15 to 100°C, preferably 20 to 90°C, more preferably 25 to 85°C, in particular at the reflux temperature of the polar protic solvent. After filtration in step f), the filter residue may be washed with a polar protic solvent which is preferably a linear or branched ^C ₄ alcohol, more preferably 2-propanol, and the filtrate and the washing solvent are combined and represent the combined filtrates. In step g), the combined filtrates of step e) are cooled and optionally stirred for crystallisation of the compound of formula II or II' at a temperature of about -20 to 30°C, preferably -20 to -10°C, more preferably -10 to -8°C, wherein cooling and optional stirring is preferably carried out for 2 to 3 h. Preferably, the crystals of the compound of formula II which formed in said combined filtrates are separated and washed with a polar protic solvent, preferably linear or branched Ci-C ₄ alcohols, more preferably 2-propanol, wherein said protic solvent preferably has a temperature of about -20 to 30°C, preferably -20 to -10°C, more preferably -10 to -8°C. The crystals of the compound of formula II or ΙΓ can be dried under normal or reduced pressure, preferably at reduced pressure, at 20°C for 2 h, preferably at 40 to 45 °C for 7 h.

Preferably, the compound of formula II or ΙΓ produced by the aforementioned processes and purified by at least one of the above described step a) to g) has a purity of 99.7 to 99.95% measured by HPLC.

The following examples are merely illustrative of the present invention and they should not be considered as limiting the scope of the invention in any way. The examples and modifications or other equivalents thereof will become apparent to those versed in the art in the light of the present entire disclosure.

Examples Methods:

HPLC purity determinations

1. Reagents and reference substances

Acetonitrile Far UV e. g. Fisher art.-no. A/0627/17

Potassium dihydrogen phosphate e. g. Merck art.-no. 1.04871

ortho-Phosphoric acid 85% e. g. Merck, art.-no. 1.00563

Water HPLC quality

2. Solutions to be prepared

Buffer solution pH 3.0

5.45 g potassium dihydrogen phosphate are dissolved in 1900 ml water. The pH of this solution is adjusted to 3.0 ± 0.05 with ortho-phosphoric acid 85%. Afterwards, the solution is filled-up to 2000.0 ml with water and filtered through a membrane filter (0.45 μηη). Solvent

Buffer solution pH 3.0 : Acetonitrile in the relation 1 : 1 (V7V) Test solution

50.0 mg of substance are dissolved with solvent to 25.0 ml (c

The test solution is prepared once.

3. Chromatographic system

Preparation of compound of formula II' (anastrozole)

Example 1 and variations thereof: Preparation of compound of formula II' (anastrozole) by using toluene as the solvent and a phase transfer catalyst

A) Employing toluene in a ratio of approx. 9 : 1 (v/m) relative to compound of formula Γ A solution of Γ (2 = Br, 328.9 g, 1.0 mol) in toluene (1.32 L) was added to a stirred mixture of K ₂ C0 ₃ (179.7 g, 1.3 eq.), 1 ,2,4-triazole (72.5 g, 1.05 eq.), PEG 600 (30.0 g, 0.05 eq.), and toluene (1.65 L) at 40 - 45 °C. After stirring for 3 h at 44 - 45 °C, the mixture (II' : III' = 8: 1 , calcd.) was filtered and the residue (III', approx. 41 g, 14 %, purity: 81.2 %), was washed with warm toluene (0.5 L). The filter residue was washed with water and dissolved in warm methanol (500 mL). The resulting solution was evaporated to dryness to give 40.9 g (13.9 %) of isomer III' (81.2 %, HPLC). The filtrate was washed with water, obtaining 3.56 L of a solution of compound II'. HPLC: 89.4 % of compound II', 3.5 % of isomer III' (3.5 %), corresponding to an isomeric ratio of approx. 26:1 (ΙΓ : III'). Yield: (91.3 %, calcd.). In the following Examples 1 B) to D), the ratio (v/m) of volume of toluene relative to mass of compound of formula Γ was varied: B) Employing toluene in a ratio of approx. 3 : 1 (v/m) relative to compound of formula I' Similar to example 1 , item A). Yield: 42.14 g (71.8 %) HPLC: 78.1 % of compound II', 7.16 % of isomer III', corresponding to an isomeric ratio of approx. 1 1 :1 (ΙΓ : III').

C) Employing toluene in a ratio of approx. 7 : 1 (v/m) relative to compound Γ

Similar to example 1 , item A). Yield: 56.91 g (97.0 %), HPLC: 86.2 % of compound II', 4.78 % of isomer III', corresponding to an isomeric ratio of approx. 18: 1 (Ι : III').

D) Employing toluene in a ratio of approx. 10 : 1 (v/m) relative to compound

Similar to example 1 , item A). Yield: 28.88 g (98.4 %), HPLC: 88.8 % of compound II', 3.25 % of isomer III', corresponding to an isomeric ratio of approx. 27: 1 (Ι : III").

In the following Examples 1 E) to 1 H), the kind of base and/or the amount of base and/or the reaction temperature was varied: E) Employing 2.2 eg of KtOBu

Similar to example 1 , item A) but stirring at 9 - 21 °C for 4.5 h. Yield: quantitative. HPLC: 75.16 % of compound ΙΓ, 3.05 % of isomer III', corresponding to an isomeric ratio of approx. 25:1 (ΙΓ : III'). F) Employing 1.2 eg of KtOBu

Similar to example 1 , item E. Yield: quantitative, HPLC: 75.38 % of compound II', 3.39 % of isomer III', corresponding to an isomeric ratio of approx. 22: 1 (Ι : III').

G) Employing 1 .1 eg. of Κ _? 00 ₃

Similar to example 1 , item A) but employing toluene in a ratio of 6 : 1 (v/m) relative to compound I' and heating at 41 - 60 °C for 9.5 h. Yield: 76.94 g (105 %). HPLC: 81.9 % of compound II', 8.45 % of isomer III', corresponding to an isomeric ratio of approx. 10:1 (ΙΓ : III').

H) Employing 2.2 eg. of K _? CO^

Similar to example 1 , item D). Yield: 54.6 g (93.1 %). HPLC: 89.2 % of compound II', 4.13 % of isomer III', corresponding to an isomeric ratio of approx. 22: 1 (Ι : III'). In the following Examples 1 I) to M), the kind of phase transfer catalyst and/or the amount thereof and/or the reaction temperature was varied:

I) Employing PEG 600, 0.03 eg.

Similar to example 1 , item D) but stirring at 52 - 53 °C for 3.5 h. Yield: 27.05 g (92.2 %) HPLC: 88.6 % of compound ΙΓ, 4.43 % of isomer III', corresponding to an isomeric ratio of approx. 20: 1 (II' : III').

J) Employing PEG 600. 0.1 eg.

Similar to example 1 , item D) but stirring at 10 - 20 °C for 4.0 h. Yield: 28.94 g (98.6 %) HPLC: 89.3 % of compound ΙΓ, 3.54 % of isomer III', corresponding to an isomeric ratio of approx. 25: 1 (II' : III').

K) Employing PEG 400. 0.05 eg.

Similar to example 1 , item D) but employing K ₂ C0 ₃ in a ratio of 1.5 eq and stirring at 40 - 45 °C for 2.75 h. Yield: 53.0 g (90.3 %) HPLC: 89.0 % of compound II', 3.78 % of isomer III', corresponding to an isomeric ratio of approx. 24: 1 (Ι : III').

L) Employing PEG 400. 0.075 eg.

Similar to example 1 , item D) and stirring at 40 - 45 °C for 4 h Yield: 50.91 g (86.8 %). HPLC: 89.3 % of compound II', 2.42 % of isomer III', corresponding to an isomeric ratio of approx. 37: 1 (II' : III').

M) Employing TBAB, 0.062 eg.

Similar to example 1 , item G) but employing TBAB (0.062 eq.) as the phase transfer catalyst, a mixture of K ₂ C0 ₃ and KOH (1 : 1 , n/n) in a ratio of 1.2 eq. relative to the compound of formula Γ and 1 .2 eq. of 1 ,2,4-triazole relative to the compound of formula I'. The mixture was heated at 28 - 34 °C for 4 h. Yield: 5.22 g (88.9 %), HPLC: 85.4% of compound ΙΓ, 5.5% of isomer III', corresponding to an isomeric ratio of approx. 15: 1 (Ι : III').

In the following Examples 1 N) and O), the amount of 1 ,2,4-triazole was varied: N) Employing 1 ,2,4-triazole, 1.0 eg.

Similar to example 1 , item A) but employing K ₂ C0 ₃ in a ratio of 1.1 eq., and toluene in a ratio of approx. 6 : 1 (v/m) relative to compound I'. Yield: 12.3 g (94.6 %). HPLC: 83.4 % of compound IP, 4.18 % of isomer III', corresponding to an isomeric ratio of approx. 20: 1 (ΙΙ':ΙΙΓ). O) Employing 1 ,2,4-triazole, 1 .1 eq.

Similar to example 1 , item A) but employing K ₂ C0 ₃ in a ratio of 1.3 eq., and toluene in a ratio of approx. 10: 1 (v/m) relative to compound I'. Yield: 28.10 g (95.8 %) HPLC: 85.3 % of compound ΙΓ, 3.27 % of isomer III*, corresponding to an isomeric ratio of approx. 26: 1 (ΙΓΙΙΓ).

Example 2: Preparation of compound of formula II' (anastrozole) by employing MtBE as the solvent and a PEG phase transfer catalyst

A mixture of I' (Z = Br, 19.73 g, 60 mmol), 1 ,2,4-triazole (4.15 g, 1.0 eq.), K ₂ C0 ₃ (9.12 g, 1.1 eq.), PEG 600 (1 .86 g, 0.05 eq.) and MtBE (300 mL) was stirred for 6.25 h at reflux (approx. 55 °C). The mixture was filtered and filter cake was washed twice with MtBE (10 mL). The filtrates were cooled to crystallization and filtered. The crystals were washed four times with MtBE (10 mL) and dried. HPLC: isomeric ratio of approx. 27 : 1 (II' : III').

Comparative Example 1 : Preparation of compound of formula ΙΓ (anastrozole) by using TBAB as the phase transfer catalyst and less suitable solvents A) Employing Dichloromethane as the solvent

A mixture of 1 ,2,4-triazole (1.38 g, 1.0 eq.), TBAB (0.4 g, 0.062 eq.) and dichlormethane (30 mL) was charged. Aq. sodium hydroxide (18.87 N , 6.4 mL, 6.0 eq.), Γ (Z = Br, 6.58 g, 20 mmol) and dichlormethane (10 mL) were added. The mixture was stirred for 2 h at ambient temperature and 2.5 h at reflux. Water (30 mL) was added and the phases were separated. The organic phase was washed with water (3 x 30 mL) and evaporated to give 6.28 g (107.0 %) of an isomeric mixture of compounds Ι and III* (7.3 : 1 ).

B) Employing ethyl acetate as the solvent

A mixture of I' (Z = Br, 6.58 g, 20 mmol), 1 ,2,4-triazole (1.38 g, 1.0 eq.), PEG 600 (0.6 g, 0.05 eq.), K ₂ C0 ₃ (6.08 g, 2.2 eq.) and ethyl acetate (40 mL) was stirred for 5 h at ambient temperature and 1.5 h at 31 - 41 °C. The solution was washed with water (3 x) and evaporated to dryness to yield 6.3 g (106.8 %) of a mixture of compounds ΙΓ and III' (4 : 1).

The solvents used in A) and B) are less suitable compared to e.g. toluene, as they are less suitable in forming precipitates of undesired side product (isomer compound of formula III'). Example 3: Preparation of compound of formula ΙΓ (anastrozole) employing a suitable solvent, without using a phase transfer catalyst

Similar to example 1 , item G) using toluene as solvent, but employing 1 .4 eq. of K ₂ C0 ₃ and 1.1 eq. of 1 ,2,4-triazole, relative to the compound of formula F and no phase transfer catalyst. The mixture was heated at 75 °C for 6 h. Yield: 69.20 g (94.4 %). HPLC: 77.22 % of compound IF, 5.57 % of isomer III', corresponding to an isomeric ratio of approx. 14: 1 (IF : III').

Comparative Example 2: Employing different kinds of less suitable solvents and without using a phase transfer catalyst

A) Employing acetonitrile as the solvent

A mixture of F (Z = Br, 3.05 g, 10 mmol), 1 ,2,4-triazole (3.96 g, 5.7 eq.), and acetonitrile (26 mL) was stirred for 5 h under reflux. The solvent was distilled off under reduced pressure at 70 °C and ethyl acetate (80 mL) was added. The solution was washed with water (3 x), dried over sodium sulphate and evaporated to dryness to yield 2.8 g (88.2 %) of an isomeric mixture of compounds IF and III' (1 : 1 ).

B) Employing acetone as the solvent

A mixture of F (Z = Br, 3.05 g, 10 mmol), 1 ,2,4-triazole (0,76 g, 1.1 eq.), K ₂ C0 ₃ (2, 1 g, 1.5 eq.) and acetone (200 mL) was stirred for 2 h under reflux. The mixture was allowed to reach room temperature and filtered. The filter residue was washed with acetone and the filtrates were evaporated under reduced pressure to give 3.14 g (99,3 %) of an isomeric mixture of compounds IF and III' (5.1 : 1). C) Employing n-butanol as the solvent

A mixture of 1 ,2,4-triazole (4.35 g, 1.05 eq.), KOH (5,05 g, 1.5 eq.) and 1-butanol (280 mL) was heated to distillation and 100 mL of solvent was distilled of at 44-57°C under reduced pressure. Then n-butanol (100 mL) and F (Z = Br, 19.73 g, 60 mmol) were added, the mixture was stirred for 3.5 h at 42 - 48 °C and filtered. The filtrates were washed six times with water (40 mL) and the organic phase was evaporated under reduced pressure to give 18.94 g (107.6 %) of an isomeric mixture of compounds IF and III' (5.5 : 1 ). D) Employing DMF as the solvent

A solution of Γ (Z = Br, 7.23 g, 23.7 mmol) in dimethylformamide (20 mL) was added to a stirred mixture of K ₂ C0 ₃ (4.9 g, 1.5 eq.), 1 ,2,4-triazole (1.8 g, 1.1 eq.) and dimethylformamide (20 mL) at 2 - 3 °C. After heating to ambient temperature over a period of 2 h and stirring for 2 h at 22 - 25 °C, potable water (130 mL) was added and the mixture was extracted twice with ethyl acetate (50 mL). The organic phase was washed three times with potable water (40 mL), dried over sodium sulphate and evaporated to dryness to yield 6.7 g (89.5 %) of an isomeric mixture of compounds Ι and III' (9.7 : 1 ).

The solvents used in A) to D) are less suitable compared to e.g. toluene, as they are less suitable in forming precipitates of undesired side product (isomer compound of formula III').

Purification of a compound of formula II' (anastrozole)

Example 4: Purification of a compound of formula II' (anastrozole) via its acid addition salt

A fraction (784 g) of the solution obtained according to example 1 item A), was extracted with HCI (aq., 1 N, 240 mL). The organic layer was treated with cyclohexane (870 mL), extracted with HCI (aq., 1 N, 66 mL, 4 x), and discarded. The combined aqueous phases were washed with toluene (70 mL). The aqueous phase was subsequently treated with toluene (525 mL) and NaOH (aq., cone, 26 mL) with stirring. The organic phase was separated and washed with water. The solvent was removed under reduced pressure and ethyl acetate was added to obtain 640 mL of a turbid solution, containing 57.5 g (97 %) of compound II'. The mixture was treated with Si0 ₂ with stirring and filtered over a bed of Si0 ₂ . The residue was successively washed with ethyl acetate and the combined clear filtrates were taken to dryness under reduced pressure.

Example 5: Further purification of a compound of formula ΙΓ (anastrozole) by recyrstallization A) Re-crystallisation from toluene (1 :4, m/v)

A fraction (174.2 g) of a crude product obtained similar to example 4 was treated with toluene (700 mL) and activated charcoal. The mixture was heated to reflux and filtered. The filter residue was washed with hot toluene and the filtrate was cooled to approximately -7 °C. The resulting suspension was stirred for 3.5 h at -7 °C and filtered. The crystals were washed once with cold toluene (35 mL), four times with cooled 2-propanol (35 mL) and dried. Yield: 159 g (91.3 %) of a colourless crystalline powder. Mp.: 83.6 - 84.3 °C. DSC: peak at approx. 84 °C. Purity: 99.94 % (HPLC). Assay (HCI0 ₄ ): 100.1 %. Heavy metals: nmt 20 ppm. Loss on drying: 0.10 %. Sulphated ash: 0.03 %. ¹ H-NMR (CDCI ₃ , 300 MHz, ppm): δ 1 .7 (s, 12 H, CH ₃ ), 5.4 (s, 2 H, CH ₂ ), 7.3 (s, 2 H, CH), 7.5 (s, 1 H, CH), 8.0 (s, 1 H CH), 8.2 (s, 2 H, CH). ¹³ C-NMR (CDCI ₃ , 75 MHz, ppm): 5 29.0, 37.2, 53.0, 122.1 , 123.8, 124.3, 136.7, 143.3, 143.4, 152.3. IR (KBr, cm ^"1 ): 3103, 2985, 2236 _{{v CN} ), 1607, 1502, 1476, 1369, 1359, 876. GC/MS (El, m/z): 293.1 [Mf .

B) Recrystallisation from 2-propanol (1 :8, m/v)

A fraction (43.5 g) of the residue obtained according to example 4 was treated with 2- propanol (370 mL) and activated charcoal. The mixture was heated to reflux and filtered. The filter residue was washed with hot 2-propanol and the filtrate was cooled to approximately - 8 °C. The resulting suspension was stirred for 2.5 h at -8 to -10 °C and filtered. The crystals were separated by filtration, washed three times with 12.5 mL of cooled 2-propanol and dried. Yield: 40.1 g (92 %) of a colourless crystalline powder (mp. 84 °C). Purity: 99.85 % (HPLC). DSC: peak at approx. 84 °C.

C) Re-crystallisation from 2-propanol (1 :4, m/v)

Similar to example 5, item B) but employing 2-propanol in a ratio of 1 :4 (m/v) relative to the distillation residue obtained according to example 1 , item A). Yield: 236.9 g (94.8 %). D) Re-crystallisation from 2-propanol (1 :2, m/v)

Similar to example 4, item B) but employing 2-propanol in a ratio of 2: 1 (m/v) relative to the distillation residue obtained according to example 1 , item A). Yield: 74.0 g (95.2 %). Mp.: 83.9 - 84.3 °C. DSC: peak at approx. 85 °C. Purity: 99.93 % (HPLC). Heavy metals: nmt 20 ppm. Loss on drying: 0.04 %. Sulphated ash: 0.02 %. Assay: (HCI0 ₄ ): 100.3 %.

E) Re-crystallisation from 1-propanol (1 :4, m/v)

Similar to example 4, item B) but employing 1 -propanol in a ratio of 1 :4 (m/v) relative to the distillation residue obtained according to example 1 , item A). Yield: 8.56 g (85.6 %). Purity: 99.96 % (HPLC).

F) Re-crystallisation from cyclohexane Compound ΙΓ (0.1 g) was dissolved in cyclohexane (20.3 mL) at reflux temperature. The mixture was cooled slowly until crystallization was observed. The crystals were separated by filtration and dried at 40 °C under reduced pressure. Yield: 0.08 g (80 %) G) Re-crystallisation from cyclohexane and ethyl acetate (1 : 1 )

Compound Ι (5 g) was dissolved in a mixture of ethyl acetate and cyclohexane (10 mL / 10 mL) at reflux temperature and cooled slowly until crystallization was observed. The crystals were separated by filtration and dried under reduced pressure. Yield: 3.15 g (63.0

%)

H) Re-crystallisation from chloroform

Compound ΙΓ (2 g) was dissolved in chloroform (10 mL) at ambient temperature and the solvent was slowly evaporated. Yield: 1.65 g (82.5 %).