Massenspektrometrische Untersuchung von Amiden. VIII—Vinyloge α-Spaltung und Nachbargruppenbeteiligung bei der Fragmentierung von Piperididen α,β-ungesättigter Carbonsäuren

The electron-impact-induced fragmentation of piperidides from β-substituted α, β-unsaturated carboxylic acids proceeds preferentially via 4-membered cyclic transition states. The development of a 6-membered ring, which is typical for α,β-unsaturated esters, occurs only to a minor extent. The mechanism of the reaction is best rationalised by the assumption of a vinylogous α-cleavage and a simultaneous neighbouring group participation of the amide function