Chemo-selective cross reaction of two enals: Via carbene-catalyzed dual activation

Abstract

A dual catalytic chemo-selective cross-coupling reaction of two enals is developed. One enal (without α-substitution) is activated by an NHC catalyst to form an acylazolium enolate intermediate that undergoes Michael-type addition to another enal molecule bearing an alkynyl substituent. Mechanistic studies indicate that non-covalent interactions between the alkynyl enal and the NHC·HX catalyst play important roles in substrate activation and enantioselectivity control. Many of the possible side reactions are not observed. Our reaction provides highly chemo- and diastereo-selective access to chiral lactones containing functionalizable 1,3-enyn units with excellent enantioselectivities (95 to >99% ee).