Studies toward the total synthesis of glycinoeclepin A

Abstract

Studies directed toward the synthesis of the A-ring portion of glycinoeclepin A are described. The enantioselective synthesis of key diketone intermediate 128 in four steps from 2,2-dimethyl-1,3-cyclohexanedione (5) has been accomplished via the acid-catalyzed intramolecular Michael cyclization of an enone generated in situ from 132. In the course of these studies, a new method for the preparation of the highly reactive a-alkynyl acroleins was developed. Several methods for the further elaborations of diketone 128 to the key enyne intermediate 95 were investigated and the best route developed to date involves the conversion of the methyl ketone to a vinyl triflate (177) followed by Sonogashira coupling. In addition, the conversion of diketone 128 to the vinyl halide 258 via a Shapiro strategy was achieved and model studies were carried out on the synthesis of vinylallene by coupling cuprate derivatives of this intermediate with propargyl alcohol derivatives.