Expedient Access to 2,3-Dihydropyridines from Unsaturated Oximes by Rh(III)-Catalyzed C–H Activation

α,β-Unsaturated
oxime pivalates are proposed to undergo
reversible C­(sp2)–H insertion with cationic Rh­(III)
complexes to furnish five-membered metallacycles. In the presence
of 1,1-disubstituted olefins, these species participate in irreversible
migratory insertion to give, after reductive elimination, 2,3-dihydropyridine
products in good yields. Catalytic hydrogenation can then be used
to convert these molecules into piperidines, which are important structural
components of numerous pharmaceuticals.