Patent ID: 6881839

Claim:
A process for preparing diltiazem comprising: (a) preparing a diol by synthesizing (2R,3S)-(−)-Ethyl-2,3-dihydroxy-3-(4-methoxyphenyl)propionate using a recyclable multifunctional catalyst of the formula IE-PdOsW wherein IE is an ion exchanger, wherein the synthesis comprises tandem or simultaneous Heck coupling of ethyl acrylate and 4-haloanisole, and N-oxidation of an amine using hydrogen peroxide, for asymmetric dihydroxylation in the presence of a cinchona alkaloid compound and in a solvent, (b) converting the diol without further crystallization into a cyclic sulfite by dissolving the diol in a solvent and reacting with thionyl chloride, (c) reacting the cyclic sulfite 2-aminothiophenol in the presence of Fe 3+ -exchanged clay in xylene to obtain a corresponding cyclic lactam, (d) subjecting the cyclic lactam to N-alkylation and acylation to obtain diltiazem.