Lanthanide Triflate Catalyzed Imino Diels-Alder Reactions; Convenient Syntheses of Pyridine and Quinoline Derivatives

Abstract

Lanthanide triflate catalyzed imino Diels-Alder reactions of imines with dienes or alkenes have been developed. A new group of Lewis acids, lanthanide triflates, are quite effective for the catalytic activation of imines. Unique reactivities of imines which work as both dienophiles and azadienes under certain conditions have been revealed. Three-component coupling reactions between aldehydes, amines, and dienes or alkenes were successfully carried out by using lanthanide triflate as a catalyst to afford pyridine and quinoline derivatives in high yields. The Lewis acid catalysts were stable and kept their activity even in the presence of water and amines. A stepwise reaction mechanism for these reactions is suggested from the experimental results.