Ketenimines from Isocyanides and Allyl Carbonates: Palladium-Catalyzed Synthesis of β,γ-Unsaturated Amides and Tetrazoles

The reaction of allyl ethyl carbonates with isocyanides in the presence of a catalytic amount of Pd(OAc)2 provided ketenimines through b-hydride elimination of the allyl imidoylpalladium intermediates. The insertion of the isocyanide into the p-allyl Pd complex proceeded via an unusual h1-allyl Pd species. The resulting ketenimines were hydrolyzed to b,g-unsaturated carboxamides during purification by flash column chromatography on silica gel or converted in situ into 1,5-disubstituted tetrazoles by [3+2] cycloaddition with hydrazoic acid or trimethylsilyl azide.