α-Oxo-Ketenimines from Isocyanides and α-Haloketones: Synthesis and Divergent Reactivity

The palladium-catalyzed reaction of a-haloketones with isocyanides afforded -oxo-ketenimines through alpha-hydride elimination of the beta-oxo-imidoyl palladium intermediates. Reaction of these relatively stable alpha-oxo ketenimines with nucleophiles such as hydrazines, hydrazoic acid, amines, and Grignard reagent afforded pyrazoles, tetrazole, beta-keto amidines, and enaminone, respectively, with high chemoselectivity. Whereas amines attack exclusively on the ketenimine functions, the formal [3+2] cycloaddition between N-monosubstituted hydrazines and alpha-oxo-ketenimines was initiated by nucleophilic addition to the carbonyl group.