Photoinduced Reactions. LXVIII. Photochemical Dehydrogenation of Imidazolines to Imidazoles

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Abstract
Imidazolines were found to be dehydrogenated to imidazoles by irradiation at 2537 Å or above 2900 Å in acetone. The n,π* triplet acetone acts as a hydrogen-abstracting agent giving 4- and/or 5-imidazolinyl radicals which in turn are transformed into imidazoles. This scheme is supported by the fact that the AIBN-initiated dehydrogenation of imidazolines gave corresponding imidazoles, that oxygen quenched the photochemical dehydrogenation, and that in some cases coupling products between the imidazolinyl and the acetone ketyl radicals were formed. Various data indicate that the imidazolinyl radical reverts to the parent imidazoline by hydrogen transfer from the acetone ketyl radical during the course of photolysis.

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