The Photochemistry of α,Β-Unsaturated Nitro Compounds and Nitronic Acids. Concerning Deconjugation and α,Β-Unsaturated Ketone Formation

The photochemistry of cyclohexylidenenitromethane (6), 3-ethyl-2-nitropent-2-ene (7), (Z)-α-methyl-α- nitrostilbene (12), (E)-3-methyl- 1-nitro-1-phenylbut-1-ene (15) and 4,4-dimethyl-3-nitro-5α-cholest-2- ene (27) has been examined to determine the structural features required for deconjugation to the β, γ-unsaturated isomer. The mechanism of the light-induced formation of the corresponding α, β- unsaturated ketone , which may accompany deconjugation , has also been examined. Support for a scheme involving γ-hydrogen abstraction to give an unsaturated nitronic acid, followed by N- hydroxyoxaziridine formation and collapse to the ketone, is provided in the photochemistry of the stable nitronic acids, 4-t-butyl-aci-nitrocyclohexane (17) and 9-aci-nitrofluorene (18). Syntheses of the nitro olefins (6), (7), (12), (15) and (27), and the nitronic acid (17) are also reported.