Reactions of condensed N-heteroaromatic molecules. Part III. Photochemical reactivity and acylation of N-acyldibenz[b,f]azepines and derivatives

Abstract

Unsensitised and benzophenone-sensitised irradiation of N-acyl, -aroyl, -carbamoyl, and -ethoxycarbonyl derivatives of 5H-dibenz[b,f]azepine (1)(iminostilbene) gives good yields of tetrabenzo[b,b′,f,f′]cyclobuta[1,2-d:3,4-d′]-bisazepines (14)–(19). Similarly, mixed cycloadducts are formed with N-methyl- and N-phenyl-maleimide. Quenching experiments suggest that triplet states of the iminostilbene derivatives are involved, and it is thought that the mixed cycloadducts arise via exciplexes. In contrast, the parent compound (1) and its N-alkyl derivatives are photochemically inactive, whereas the N-tosyl compound undergoes photo-Fries rearrangement. Although electrophilic substitution in dibenz[b,f]azepine apparently occurs at the 2- and 8-positions, the 5-acetyl derivative undergoes Friedel–Crafts acylation exclusively at the 10(11)-position. Photoelectron spectra reveal that ionisation potentials of N-alkyldibenzazepines are considerably less than those of the corresponding N-acyl derivatives.