Unexpected Catalytic Reactions of Silyl-Protected Enol Diazoacetates with Nitrile Oxides That Form 5-Arylaminofuran-2(3H)-one-4-carboxylates

Silyl-protected enol diazoacetates undergo dirhodium(II)-catalyzed reactions with nitrile oxides to form acid-labile ketenimines via dipolar cycloaddition of nitrile oxides to a donor/acceptor cyclopropene and Lossen rearrangement of the dipolar adduct; acid catalysis converts the ketenimine to the furan product.