Stereoselective Synthesis of Diltiazem via Dynamic Kinetic Resolution

Abstract

An efficient synthesis of diltiazem has been developed using dynamic kinetic resolution (DKR) as a key step. The methyl (2S,3S)-2-chloro-3-hydroxy-3- (4-methoxyphenyl)propionate was synthesized from a racemic mixture of α-chloro-β-keto ester, with high anti diastereoselectivity (92%) and enantioselectivity (95%), based on an asymmetric hydrogenation reaction with a chiral ruthenium(II) catalyst, simply prepared by mixing Ru(cod)(2-methylallyl) 2 with the atropisomeric ligand (S)-MeO-BIPHEP. By treatment of this α-chloro-β-hydroxy ester with a base, the corresponding trans methyl glycidate, a key intermediate of diltiazem, was easily obtained.