Controlled β-protonation and [4+2] cycloaddition of enals and chalcones via N-heterocyclic carbene/acid catalysis : toward substrate independent reaction control

A substrate-independent selective generation of enolates over homoenolate equivalents in NHC-catalyzed reactions of enals and chalcones is disclosed. Acid co-catalysts play vital roles in control of the reaction pathways, allowing for individual access to diverse products from identical substrates