Process for preparation of ospemifene

1. A process for the preparation of ospemifene, a compound of formula I,

and pharmaceutically acceptable salts thereof, the process comprising:

(a) providing an isomeric mixture of Z,E-4-(4-hydroxy-1,2-diphenylbut-1-enyl)phenol;

(b) separating the desired Z-isomer, a compound of formula IIa, or a salt thereof and the undesired E-isomer, a compound of formula IIb, or a salt thereof from the isomeric mixture of Z,E-4-(4-hydroxy-1,2-diphenylbut-1-enyl)phenol;

(c) recycling the undesired E-isomer, the compound of formula IIb, or a salt thereof to generate an isomeric mixture of Z,E-4-(4-hydroxy-1,2-diphenylbut-1-enyl)phenol;

(d) optionally, repeating steps (b) and (c);

(e) converting the Z-isomer of 4-(4-hydroxy-1,2-diphenylbut-1-enyl)phenol, the compound of formula IIa, or a salt thereof obtained in step (b) to ospemifene; and wherein the undesired E-isomer, the compound of formula IIb, or a salt thereof is recycled to generate an isomeric mixture of Z,E-4-(4-hydroxy-1,2-diphenylbut-1-enyl)phenol by a process comprising:

(i) providing a solution of the E-isomer, the compound of formula IIb, or a salt thereof, in a solvent;

(ii) stirring and/or heating the solution obtained in step (i) to generate an isomeric mixture of Z,E-4-(4-hydroxy-1,2-diphenylbut-1-enyl)phenol; and

(iii) isolating the isomeric mixture of Z,E-4-(4-hydroxy-1,2-diphenylbut-1-enyl)phenol.

2. The process of claim 1 , wherein the desired Z-isomer, the compound of formula IIa, or a salt thereof is separated from the undesired E-isomer, the compound of formula IIb, or a salt thereof by a process comprising:

(i) subjecting the isomeric mixture of Z,E-4-(4-hydroxy-1,2-diphenylbut-1-enyl)phenol to treatment with a base in a solvent to generate a reaction mixture;

(ii) separating the desired Z-isomer, the compound of formula IIa, or a salt thereof and the undesired E-isomer, the compound of formula IIb, or a salt thereof from the reaction mixture obtained in step (i); and

(iii) optionally, treating the separated Z-isomer, the compound of formula IIa, or a salt thereof and the E-isomer, the compound of formula IIb, or a salt thereof with an acid.

3. The process of claim 2 , wherein the desired Z-isomer, the compound of formula IIa, or a salt thereof and the undesired E-isomer, the compound of formula IIb, or a salt thereof are separated from the reaction mixture obtained in step (i), by any of the following:

(x) by carrying out step (i) in a solvent in which one of the isomers, or salt thereof is soluble and the other isomer, or salt thereof is insoluble and precipitates out; or

(y) by carrying out step (i) in a solvent and by adding an anti-solvent to it wherein one of the isomers, or salt thereof is precipitated out; or

(z) by removing the solvent of step (i) and adding a second solvent to it in which one of the isomers, or salt thereof is soluble and the other isomer, or salt thereof is insoluble and precipitates out.

4. The process of claim 3 , wherein the solvent in step (x) is selected from ketones, haloalkanes, hydrocarbons, water, or mixtures thereof.

5. The process of claim 1 , wherein the step (ii) is carried out at a temperature in the range of 10° C. to 150° C.

6. The process of claim 1 , wherein the step (ii) is carried out until the content of the Z-isomer, the compound of formula IIa, is not less than 48% in the isomeric mixture of Z,E-4-(4-hydroxy-1,2-diphenylbut-1-enyl)phenol.

7. The process of claim 1 , wherein the Z-isomer of 4-(4-hydroxy-1,2-diphenylbut-1-enyl)phenol, the compound of formula IIa, or a salt thereof is converted to ospemifene by a process comprising:

(i) reacting the Z-isomer, the compound of formula IIa, or a salt thereof with a compound of formula III,

wherein X is selected from the group consisting of Cl, Br, and I, to form a compound of formula IV;

(ii) converting the compound of formula IV to a compound of formula V;

and

(iii) deprotecting the compound of formula V to ospemifene.

8. The process of claim 7 , wherein the compound of formula IV is converted to the compound of formula V using oxalyl chloride and dimethyl formamide.

9. The process of claim 7 , wherein the compound of formula V is deprotected by hydrogenation using a palladium catalyst in the presence of an acid to give ospemifene.

10. The process of claim 1 , wherein the level of E-isomer of ospemifene is less than 0.10% w/w with respect to ospemifene, as determined by high performance liquid chromatography (HPLC).

11. The process of claim 7 , further comprising the steps of:

(a) providing a solution of ospemifene in a solvent selected from alcohols, nitriles, water, or mixture thereof;

(b) precipitating out ospemifene from the solution obtained in step (a); and

(c) isolating the solid formed in step (b) to give ospemifene, having a D 50 particle size in the range of about 15 microns to about 75 microns and D 90 particle size in the range of 50 microns to about 150 microns.

12. The process of claim 11 , wherein the step (a) is carried out at a temperature in the range of 40° C. to 120° C.

13. The process of claim 11 , wherein the step (b) is carried out at a temperature in the range of −5° C. to 30° C.

14. The process of claim 11 , wherein the step (b) is carried out without stirring the solution of ospemifene.