MECHANISTIC STUDIES ON THE PHOTO-CHEMICAL CONVERSION OF ENAMINONITRILES TO IMIDAZOLES

Imidazoles are not formed by photolysis of the N, N-disubstituted enaminonitriles, 2-(dimethylamino)-1-cyclohexene-1-carbonitrile (7) and 3-(dimethylamino)acrylonitrile (5). These results show that the enaminonitrile must contain an NH group for the photochemical formation of the imidazole to proceed. N-Isopropyldiaminomaleonitrile (11) did not photodissociate to yield aminocyanocarbene (4) as shown by the absence of diaminomaleonitrile (DAMN) (1) as a photoproduct. Direct irradiation of N-isopropyliminoacetonitrile (18A) at -196 °C did not give the absorption spectrum attributed to aminocyanocarbene. Polymer formation was observed when the photolysis of 18A was performed at room temperature. Benzophenone-sensitized photolysis of 18A gave N, N'-diisopropyldiaminosuccinonitrile (19A). The reaction does not proceed by the dimerization of N-isopropylaminocyanocarbene to diisopropyldiaminomaleonitrile (15) followed by the reduction of 15, since it was observed that 19A is not formed by the benzophenone-sensitized photolysis of 15. The significance of these results to the mechanism of the photochemical rearrangement of enaminonitriles to imidazoles and the postulated role of aminocyanocarbene as an intermediate in a number of thermal and photochemical reactions are discussed. © 1979, American Chemical Society. All rights reserved.