Photoinduoed molecular transformations. Part 146. Photoacylation and photoalkylation of 2-arylamino- and 2-alkylamino-1,4-naphthoquinones

The photoacylation of 2-arylamino- or 2-alkylamino-1,4-naphthoquinones with aromatic or aliphatic aldehydes can be achieved in high yields when a solution of N-substituted 2-amino-1,4-naphthoquinones and an aldehyde in benzene is irradiated in the presence of benzophenone. Irradiation of 2-anilino-1,4-naphthoquinones and cyclic ethers, such as tetrahydrofuran or dioxane, in the presence of benzophenone led to analogous photoalkylation products, 3-alkyl-2-anilino-1,4-naphthoquinones, in high yield. 1,4-Dihydroxy-2-diphenylamino-3-propionylnaphthalene, characterized as the diacetate, could be isolated from the photoacylation of 2-diphenylamino-1,4-naphthoquinones with propanal. The photoacylation thus involves hydroquinone derivatives as intermediates. Radical processes involving the formation of acyl or alkyl radicals from aldehydes or cyclic ethers by hydrogen abstraction with excited benzophenone for these photoacylations and photoalkylations are proposed.