Rhodium(II)-catalysed intramolecular O-H insertion of alpha-diazo-gamma-azido-delta-hydroxy-beta-ketoesters. Evidence for a novel sigmatropic rearrangement of an allylic azide intermediate

The Rh-2(OAc)(4) catalyzed intramolecular O-H insertion reaction of delta-h ydroxy-alpha-diazoesters affords 3(2H)-furanone-2-carboxylates in good yiel d but with moderate selectivity (d.e. ca 60%), The initially formed 2,5-sub stituted cis-furanones were found to epimerize to the corresponding 2,5-tra ns isomers when subjected to silica gel chromatography. The Rh-2(OAc)(4) ca talyzed decomposition of gamma-azido-delta-hydroxy-alpha-diazoesters also f urnished 3(2H)-furanone-2-carboxylates. These compounds are derived by a se quential O-H insertion reaction followed by a concerted [3,3]-sigmatropic s hift of the allylic azide intermediate.