Vicinal di-functionalization of α,β-unsaturated ketones via manganese carbene intermediates: synthesis of γ-acyl-δ-lactones by cascade Michael addition/aldol/transesterification reactions

The carbene–enolate complexes generated upon reaction of the carbene anion [Cp′(CO)2MnC(OEt)CH2]− with benzylidene acetone and chalcone react with benzaldehyde to form the 6-membered oxacyclocarbene complexes Cp′(CO)2MnCCH2CH(Ph)CH(C{O}R)CH(Ph)O (R=Me, Ph). The latter, which can be regarded as the result of cascade Michael addition/aldol/transesterification reactions, are readily oxidized by air to release the corresponding γ-acyl-δ-lactones.