Modified conditions for Hantzsch thiazole synthesis provides valine- and threonine-derived thiazoles without significant loss of optical purity. This two- or three-step procedure proceeds by the cyclocondensation of the corresponding thioamide under basic conditions, according to modified methods of Meyers and Holzapfel. The hydroxythiazoline intermediate is then dehydrated by treatment with trifluoroacetic anhydride-pyridine, followed by triethylamine, according to Nicolaou’s procedure. Solvolysis of the trifluoroacetamide derivative produced in this process can be affected with sodium ethoxide in ethanol to give a reliable method for the stereoselective synthesis of functionalised thiazole building blocks in high yield.
Hantzsch - thiazoles - heterocycles - amino acids
