A Convenient Entry to 5-(sp2)-Substituted and 5,5-Disubstituted Tetronic Acids

A one-pot, convenient and general access to 5-sp2-substituted and 5,5-disubstituted tetronic acids is described. The protocol embodies two consecutive chemical events: a Michael addition of pyrrolidine on a secondary or tertiary (gamma)-hydroxy-(alpha),?-alkynyl ester derivative to give the corresponding enamine, and the subsequent acid-catalyzed hydrolysis-lactonization of this intermediate to afford the tetronic acid derivative.