Visible-Light-Driven N-Heterocyclic Carbene Catalyzed γ- and ϵ-Alkylation with Alkyl Radicals

Abstract

The merging of photoredox catalysis and N-heterocyclic carbene (NHC) catalysis for γ- and ϵ-alkylation of enals with alkyl radicals was developed. The alkylation reaction of γ-oxidized enals with alkyl halides worked well for the synthesis γ-multisubstituted-α,β-unsaturated esters, including those with challenging vicinal all-carbon quaternary centers. The synthesis of ϵ-multisubstituted-α,β-γ,δ-diunsaturated esters by an unprecedented NHC-catalyzed ϵ-functionalization was also established.

Keywords: N-heterocyclic carbenes; alkylation; photocatalysis; reaction mechanisms; synthetic methods.