The photochemical reactions of different N-(2-acylphenyl)-2-bromo-2-methylpropanamides have been investigated. Irradiation of the N-unsubstituted anilides 1a–1c gave the corresponding dehydrobromination, cyclization, and bromo-migration products 2, 3, and 4, respectively (Table 1). Irradiation of the N-alkyl anilides 1e–1g afforded the corresponding deacylation and cyclization products 5 and 6, respectively
explained by a 6π-electron cyclization only. The formation of the open-chain amides 4e–4h probably follows a mechanism involving a 1,7-diradical, C and a spirolactam of type D (Scheme). Long-range ζ-H abstraction by the excited carbonyl O-atom of the benzoyl group on the aniline ring is expected to proceed via a nine-membered cyclic transition state, as proposed on the basis of X-ray crystallographic analyses