Rhodium(II)-Catalysed Intramolecular O-H Insertion of α-Diazo-γ-Azido-δ-Hydroxy-β-Ketoesters. Evidence for a Novel Sigmatropic Rearrangement of an Allylic Azide Intermediate

Abstract

The Rh2(OAc)4 catalyzed intramolecular O-H insertion reaction of δ-hydroxy-α-diazoesters affords 3(2H)-furanone-2-carboxylates in good yield but with moderate selectivity (d.e. ca 60%). The initially formed 2,5-substituted cis-furanones were found to epimerize to the corresponding 2,5-trans isomers when subjected to silica gel chromatography. The Rh2(OAc)4 catalyzed decomposition of γ-azido-δ-hydroxy-α-diazoesters also furnished 3(2H)-furanone-2-carboxylates. These compounds are derived by a sequential O-H insertion reaction followed by a concerted [3,3]-sigmatropic shift of the allylic azide intermediate.