The Photochemical Isomerization of N-Bromo-α,β-unsaturated Lactams; An Intermolecular Allylic Bromination Process Involving a Probable Bromine Radical Chain

Abstract

The photochemical behavior of the N-bromo-α,β-unsaturated lactams 1b and 2b has been investigated with particular regard to their potential intramolecular reactions. In both cases the main product corresponds to an isomerization of bromine to the 5-position. A crossover experiment and free radical initiation by AIBN or benzoyl peroxide indicate that the reaction bears a close mechanistic analogy to the NBS reaction. It was furthermore observed that the allylic bromo derivatives prepared could be smoothly reduced to the corresponding β,γ-unsaturated lactam making available an efficient method of deconjugation of α,β-unsaturated lactams.