Tandem [2,3]sigmatropic rearrangement of a sulphonium ylide and cyclopropanation of the resulting electron-rich olefin on a 4-methoxy-2-pyrone derivative

Rhodium catalyzed reaction of 4-methoxy-6-phenylthiomethyl-2-pyrone with dimethyldiazomalonate affords 5-(bis(methoxycarbonyl))(phenylthio)methyl-4-methoxy-6-methylene-5,6- -dihydro-2-pyrone via [2,3]sigmatropic rearrangement of the corresponding sulphur ylide. Cyclopropanation of the 6-methylene double bond occurs by the less hindered side. © 1986.Financial support from CAICYT (Ministerio de Educación y Ciencia of Spain. Project 2014/83) is gratefully acknowledged