Stereoselective N-Heterocyclic-Carbene-Catalyzed Formal [4+2] Cycloaddition: Access to Chiral Heterocyclic Cyclohexenones
2023
Abstract
The present study reports an asymmetric NHC-catalyzed formal [4 + 2] cycloaddition of heterocyclic alkenes containing a polarized double bond with an azolium-dienolate intermediate generated from α-bromo-α,β-unsaturated aldehydes without external oxidation of the Breslow intermediate. Heterocyclic cyclohexenones were produced in good isolated yields (typically about 90%) with good stereochemical outcomes (in most cases, dr > 20/1, and ee = 70-99%).
The synthetic utility of the protocol was exemplified by the scope of heterocyclic alkenes.