Ceric ammonium nitrate oxidation of N-(p-methoxybenzyl)lactams: competing formation of N-(hydroxymethyl)δ-lactams

The ceric ammonium nitrate mediated oxidative deprotection of N-(p-methoxybenzyl) δ-lactams leads to the formation of an unexpected N-(hydroxymethyl) δ-lactam along with the Ndeprotected δ-lactam.In comparison, N-(p-methoxybenzyl) γ-lactams are completely deprotected under the same reaction conditions.Further studies indicated that addition of an aqueous solution of ceric ammonium nitrate to an acetonitrile solution of N-(p-methoxybenzyl) δ-lactams in the presence of 2-amino-2-methyl-1-propanol as an additive promoted N-deprotection.Ceric ammonium nitrate oxidation of N-(α,α-dideuterio-p-methoxybenzyl)-6-allyl-δ-lactam (8), revealed that the methylene unit of the N-(hydroxymethyl) group is derived from the benzylic methylene unit of the N-protecting group.A plausible reaction pathway for the formation of the N-(hydroxymethyl) δ-lactams from an N-acyliminium ion intermediate is proposed.

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