Azomethine ylide forming photoreactions

M. J. Mariano, P. S. Investigations of novel azomethine ylide-forming photoreactions of N-silylmethylimides. J. Org. Chem. 1995, 60, 2353-2360. 

Azomethine Ylide Forming Photoreactions of N-Trimethylsilylphthalimides and Related Conjugated Imides... 

This novel and preparatively useful azomethine yHde-forming photoreaction is not restricted to phthal-imide substrates." Other conjugated imides that contain N-silylmethyl substitution are transformed to their corresponding azomethine ylides by photoinduced C-to-O silyl migration reaction. 

The formation of the A-vinylaziridine 70 in the photoreaction of 68 deserves additional comment. Depending on the multiplicity, the intermediate 72 formed by path b could be a triplet 1,3-biradical. However, if intersystem crossing occurs along the reaction coordinate, the singlet biradical must be considered as a dipolar azomethine ylide. According to literature precedents, both intermediates, the 1,3-biradical and the ylide, will cyclize to form the observed aziridine. This is the first case in a DPM process where a zwitterion can be postulated as a possible intermediate. 

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