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

The palladium-catalyzed reaction of alpha-haloketones with isocyanides afforded alpha-oxo-ketenimines through beta-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.