Rh-catalyzed formation of dioxolanes from alpha-alkyl diazoesters: diastereoselective cycloadditions of carbonyl ylides with selectivity over beta-hydride elimination.

Described here is a diastereoselective Rh-catalyzed method for the preparation of dioxolanes from alpha-alkyl-alpha-diazoesters. This represents the first general method for generating carbonyl ylides from alpha-diazoesters that possess beta-hydrogens, as such diazo compounds typically give rise to alkenes via beta-hydride elimination. Subsequent cycloaddition with aromatic aldehydes gives tetrasubstituted dioxolanes with unusually high diastereoselectivity. A model is set forth to explain the diastereoselectivity of the cycloaddition.