Vicinal di-functionalization of alpha,beta-unsaturated ketones via manganese carbene intermediates: synthesis of gamma-acyl-delta-lactones by cascadeMichael addition/aldol/transesterification reactions

The carbene-enolate complexes generated upon reaction of the carbene anion [Cp'(CO)(2)Mn=C(OEt)CH2](-) with benzylidene acetone and chalcone react wit h benzaldehyde to form the 6-membered oxacyclocarbene complexes Cp'(CO)(2)M n=CCH2CH(Ph)CH(C{O}R)CH(Ph)O (R = Me, Ph). The latter, which can be regarde d as the result of cascade Michael addition/aldol/transesterification react ions, are readily oxidized by air to release the corresponding gamma-acyl-d elta-lactones. (C) 2000 Elsevier Science Ltd. All rights reserved.