Impact of Bulky Substituents on the Singlet Arylnitrene Ring Enlargement.

Substituents of the hydrindacene type allow the isolation of crystalline stable triplet arylnitrenes from photodecomposition of the corresponding aryl azides, while phenyl azide is known to produce singlet phenylnitrene that reacts to didehydroazepine via benzazirine. Comparison of computed potential energy surfaces for ring enlargement of singlet arylnitrenes suggests that bulky groups of the hydrindacene type should not significantly change the rates of formation of didehydroazepines compared to phenylnitrene. Thus, didehydroazepines could be trappable intermediates en route to stable triplet arylnitrenes.