Synthesis of substituted thiazoline carboxylic acids

摘要

A useful and efficient method of preparing an alkylated thiazoline carboxylic acid, or a derivative thereof, comprises coupling a substituted aryl nitrile such as, for example, 2,4-dimethoxybenzonitrile or 4-methoxybenzonitrile, with a cysteine ester to form a substituted thiazoline carboxylic acid ester; optionally hydrolyzing the substituted thiazoline carboxylic acid ester to form a substituted thiazoline carboxylic acid; optionally, protecting the carboxyl group; alkylating the thiazoline ring at the 4-carbon position, as indicated in Structural Formula (I), with a compound of the formula R₁-L, wherein R₁ is as defined above and L is a leaving group, in the presence of a phase transfer catalyst; and, optionally, deprotecting the carboxyl group. In one embodiment of the present invention, a cinchona-alkaloid derived phase transfer catalyst is used to alkylate a protected substituted thiazoline carboxylic acid.