STEREOSELECTIVE SYNTHESIS OF ALPHA-AMINO AND ALPHA-THIO BETA-LACTONES BY CONJUGATE ADDITION OF AMINE AND THIOL NUCLEOPHILES TO ALPHA-METHYLENE BETA-LACTONES AND THEIR DECARBOXYLATION TO ALLYLAMINES AND SULFIDES

The stereoselective, conjugate addition of secondary, cyclic amines (pyrrolidine and piperidine) and mercaptans (thiophenol, isopropyl, and benzyl thiols and beta-mercaptoethanol) to alpha-methylene beta-lactones 1 and 2 was investigated. The corresponding alpha-(aminomethyl) and alpha-(thiomethyl) beta-lactones 3-5 and 6-10 were obtained in excellent yields through protonation of the intermediary enolates. In methanol the trans isomers mere the major products, while considerable amounts of the cis isomers were formed in THF and acetone. The decarboxylation of these alpha-aminomethyl and alpha-thiomethyl beta-lactones as neat samples at 180 degrees C produced in excellent yields the corresponding allyl amines and sulfides 11-13 and 14-18 with retention of the initial beta-lactone geometry. This unprecedented sequence of Michael-type addition followed by decarboxylation, in which the alpha-methylene beta-lactones serve as allene equivalents, provides a useful alternative to the Wittig olefination for the preparation of allylic amines and sulfides.