Simple and condensed β-lactams. Part 14. Anomalous behaviour of 1-(4-methoxyphenyl)-4-(tetrazol-5-ylmethyl)azetidin-2-one towards cerium(IV) ammonium nitrate

Treatment of 1-(4-methoxyphenyl)azetidin-2-one 7 with cerium(IV) ammonium nitrate (CAN) fails to yield the N-deprotected product 6. Depending on the mode of work-up, N-substituted products 8–13 are obtained instead. The formation of these products may be rationalized by assuming interaction of the nucleophilic tetrazole and electrophilic quinone imine moieties of intermediate 21 to afford, after deprotonation, the spirocyclic quinone aminal 25. The latter, in contrast to quinone imine derivatives of type 3, is stable to hydrolysis under the conditions applied but reacts readily both with added sodium chloride and bromide as well as with reducing agents (NaHSO3, I–).