NHC-catalyzed reaction of enals with unactivated enones: substituent effect on the formation of 1 : 1 and 1 : 2 adducts

Abstract

It has been found for the first time that the imidazole carbene-catalyzed reaction of α,β-unsaturated aldehydes with unactivated enones gives two kinds of pyranones, 1 : 1 and 1 : 2 adducts, instead of cyclopentenes and cyclopentanones. The ratio of the two products was determined by the substituent effect of the enones, not by a molar ratio of the starting materials in general. Moreover, a longer reaction period caused the formation of another 1 : 2 adduct, which was derived from the 1 : 1 pyranones initially formed.