Synthesis of chiral thiazolo[3,4-a]pyrazine-5,8-diones

A synthetic approach to chiral (3R,8aR)-3-phenyltetrahydrothiazolo[3,4-a]pyrazine-5,8-diones starting from a (2S,4R)- and (2R,4R)-diastereoisomeric mixture of 2-phenylthiazolidine is described. The diastereoselective N-acylation of the thiazolidine followed by condensation with amines affords the chiral 1,3-thiazolidine-annulated system. The structure of (3R,8aR)-7-(methoxycarbonylmethyl)-3-phenyltetrahydrothiazolo[3,4-a]pyrazine-5,8-dione was determined by X-Ray crystallography.