Processes for the preparation of substituted sulfoxides
The present invention relates to a process for enantioselective synthesis of substituted pyridinylmethyl sulfinyl-benzimidazole of compound of Formula (I). The process includes enantioselective catalytic oxidation of a substituted pyridinylmethyl prochiral sulfide derivative of compound of Formula (II) with an oxidizing agent in the presence of a chiral transition metal complex and a base in the absence of an organic solvent.
1. An enantioselective catalytic oxidation process for the preparation of an optically active enantiomer or an enantiomerically enriched form of substituted pyridinylmethyl sulfinyl-benzimidazole of compound of Formula I
wherein R 1 to R 4 represent hydrogen, C 1 to C 4 represent linear or branched alkyl, C 1 to C 4 represent linear or branched alkoxy, aryl, aryloxy or its pharmaceutically acceptable salts, the process comprising oxidizing a pro-chiral sulfide of Formula II,
wherein R 1 to R 4 are the same as defined above, in the presence of a chiral transition metal complex and a base in the absence of an organic solvent.
2. The process according to claim 1 , wherein the prochiral sulfide is obtained as a solution directly from a reaction mixture in which it is formed.
3. The process according to claim 1 , wherein the reaction is carried out in the presence of an oxidizing agent.
4. The process according to claim 3 , wherein the oxidizing agent is selected from the group comprising hydrogen peroxide, alkyl hydro peroxide and aryl alkyl hydro peroxide.
5. The process according to claim 4 , wherein the aryl alkyl hydro peroxide comprises cumene hydro peroxide.
6. The process according to claim 1 , wherein the transition metal is selected from the group comprising titanium, zirconium and vanadium.
7. The process according to claim 1 , wherein the transition metal complex is prepared from a transition metal alkoxide and a chiral ligand.
8. The process according to claim 7 , wherein the transition metal alkoxide comprises titanium isopropoxide.
9. The process according to claim 1 , wherein the chiral ligand comprises a chiral branched or unbranched alkyl diol or an aromatic diol.
10. The process according to claim 9 , wherein the chiral diol is a chiral ester of tartaric acid.
11. The process according to claim 10 , wherein the chiral ester comprises (+)-diethyl L-tartrate.
12. The process according to claim 1 , wherein the metal complex is added to the reaction mixture containing prochiral sulfide.
13. The process according to claim 1 , wherein the reaction mixture containing prochiral sulfide is added to the metal complex.
14. The process according to claim 1 , wherein the base is an organic or inorganic base.
15. The process according to claim 14 , wherein the organic base is selected from the group comprising trimethylamine, triethylamine, tributylamine, triisopropylamine, diisopropylethylamine, pyridine, morpholine, DBU (1,8-diazabicyclo-[5.4.0]-undec-7-ene), DBN (1,5-diazabicyclo-[4.3.0]-non-5-ene), 4-dimethylamino pyridine and mixtures thereof.
16. The process according to claim 14 , wherein inorganic base is selected from the group comprising alkali metal carbonate, alkali metal bicarbonate and alkali metal hydroxide.
17. The process according to claim 1 , wherein the enantioselective catalytic oxidation is carried out at a temperature in the range of about 20-40° C.
18. The process according to claim 1 , wherein the enantioselective catalytic oxidation is carried out for a period of about 1-8 hours.
19. The process according to claim 1 , wherein the obtained sulfoxide is converted into a pharmaceutically acceptable salt selected from optically active alkali and alkaline earth metal salts.
20. The process according to claim 19 , wherein the optically active alkali or alkaline earth metal salt is prepared by treating with an alkali or alkaline earth metal source comprising bicarbonates, carbonates, hydrides, hydroxides, halides, sulphates and oxides.