The photochemistry of aliphatic and alicyclic α,β-unsaturated nitro compounds. A study of double bond cleavage following intramolecular cyclization and nitro-nitrite rearrangement

The light-induced intramolecular cyclization of α, β-unsaturated nitro compounds leading to double bond cleavage, which had previously been detected in a small number of β-nitrostyrenes and α-nitro-stilbenes, has been shown to occur in a range of aliphatic and alicyclic α, β -unsaturated nitro compounds. At room temperature the reaction competes to a significant extent with the well known nitro-nitrite rearrangement in the irradiation of 1-nitro-2-phenylcyclohexene (2), 1-methyl-2-nitro-cyclohexene (6), 1-methyl-2-nitrocycloheptene (11), 2-methyl-3-nitrobut-2-ene (23) and 2-nitro-3-phenylbut-2-ene (24), while it was the only reaction detected in the case of 1-methyl-2-nitrocyclo- octene (12) and 1-nitrocyclooctene (19). No evidence for the cleavage reaction was found with 1-methyl-2-nitrocyclopentene (10), 1-nitrocyclohexene (17), 1-nitrocycloheptene (18) and 3-nitropent-2-ene (25). The nitrile oxides produced in the double bond cleavage reaction were trapped in a cycloaddition with methyl acrylate, yielding 3-substituted methyl 4,5-dihydroisoxazole-5-carboxylates. Irradiations of 1-methyl-2-nitrocyclohexene (6) and 1-methyl-2-nitrocycloheptene (11) in refluxing benzene afforded only the bridged ring isoxazolines (30) and (31) respectively. Syntheses of a number of nitro-olefins are also reported.