Stereoselective piperidine synthesis through oxidative carbon–hydrogen bond functionalizations of enamides

N-Vinyl amides, carbamates, and sulfonamides that contain pendent π-nucleophiles react with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to form piperidine structures with good to excellent levels of efficiency and stereocontrol. Reactions proceed nearly instantaneously at room temperature. Transition state models show the preferred configuration around the intermediate acyliminium ion and the orientation of the nucleophile.