Light-induced reactions of 2-(N-alkyl-N-arylamino)cyclohexanones and related amino-cycloalkanones: formation of 7-azabicyclo [4.2.0] octan-1-ols

Abstract

On irradiation, 2-(N-alkyl-N-arylamino)cyclohexanones (aryl = Ph; alkyl = Me, benzyl, allyl, Et, CH₂CH₂Ph, or CH₂CF₃; or aryl =p-tolyl; alkyl = Me)(10) or (20), 4,4-dimethyl-2-(N-methylanilino)-cyclohexanone (24), and 2-(N-methylanilino)-5α-cholestan-3-one (26) underwent type-II cyclisation to afford azetidinol (7-azabicyclo [4.2.0] octan-1-ol) derivatives. In general, fission to give the corresponding N-alkyl-N-arylamine and ketone was a minor photoreaction. When the alkyl group of the 2-(N-alkyl-anilino)cyclohexanone had the structure –CH(R)CH₂R′, a double 1,5-hydrogen transfer occurred leading to a low yield of a 2-anilinocyclohexanol (31a). Photolysis of 2-anilinocyclohexanone (32a) gave a little of the direct-fission product aniline (17a), and the alkylamino-ketones 2-(NN-diethylamino)-(32b) and 2-(N-pyrrolidino)-cyclohexanone (32c) underwent no significant photoreaction in methanol. The isolation of indan-1-one and N-trideuteriomethylaniline on irradiation of 2-(N-trideuteriomethylanilino)-indan-1-one (33b) in diethyl ether indicated that the photoreaction was a direct C_α-N bond fission and not a type-II fission.