Characterization of a Didehydrobenzoxazine Intermediate in a Novel Carbene-to-Carbene Transformation

Irradiation of N(2) matrix-isolated 3-chloro-3-(2-benzoxazolyl)diazirine gives a mixture of syn- and anti-benzoxazolylchlorocarbenes which could be characterized by IR, UV/vis, and B3LYP modeling. Subsequent irradiation of the carbene caused ring opening to the corresponding quinoimine, which was similarly characterized. In turn, the quinoimine photochemically underwent ring-closure to a novel, highly strained cyclic ketenimine. Unrestricted singlet DFT calculations were required to fit the IR spectrum of the ketenimine, suggesting significant diradical character. Photolysis of the ketenimine led to ring cleavage in yet another fashion, to give an isonitrile-phenoxychlorocarbene, whose spectra were similar to those of the previously characterized phenoxychlorocarbene. Finally, at shorter wavelengths, the phenoxycarbene underwent the expected rearrangement to the corresponding benzoyl chloride.