Exocyclic a-carbon

The depropagation of ionic species may give either ionic species (an attack of oxygen atom of the terminal unit on the exocyclic a-carbon) or covalent species (an attack of counterion on exocyclic carbon). Direct conversion of covalently terminated chain into covalently terminated chain with one more unit is not possible, as well as the corresponding backward reaction. The detailed analysis of the complete reaction scheme is given in a recently published review [6]. 

Also, lactams could be hydroxylated [223] or alkoxylated [224,225] in the a-position. In the case of five- and six-membered A-alkyl lactams oxidation occurs regioselectively at the endocyclic carbon in a-position to nitrogen and at the exocyclic a-carbon with seven-... 

The anodic oxidation of A/ -alkyl- and A/ -benzyl-y3-lactams in methanol at Pt anodes in the presence of Et4NBp4 as an electrolyte leads to the methoxylation of both the endo-and exocyclic carbon in a-position to nitrogen. Usually the exocyclic carbon was more easily oxidized than the endocyclic carbon. With a tertiary exocyclic a-carbon, the formation of the endo-oxidation product was increased. A/"-Benzyl-)3-lactams were predominantly oxidized in the exocyclic a-position. In case of 7V-4-methoxybenzyl-)3-lactam exocyclic oxidation occurred with total regioselectivity [227,228]. 

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