Photochemistry of Epoxyquinone. 5. Photoinduced Cycloadditions of Epoxynaphthoquinone to Aldehydes, Ketones, and Oxygen

Article abstract of DOI:10.1021/jo00158a026

Irradation of a benzene solution of 2,3-dihydro-2,3-dimethyl-23-epoxy-1,4-naphthoquinone (3a) in the presence of aldehydes gives the primary 1,3-dioxolane adducts in good yields.Upon further irradation, the primary adducts undergo Photorearrangement to give alkylidenephthalides.A similar photocycloaddition reaction of 3a with aliphatic ketones was realized by their use as the reaction medium.When irradiated in the presence of oxygen in benzene, 3a was converted into 3-acetyl-3-acetoxyphthalide and 3-acetoxy-3-methylisochroman-1,4-dione presumably via the reaction ofsinglet oxygen with a carbonyl ylide, 4a.In contrast to 2,3-dialkylepoxynaphthoquinones 3a-d, the photoinduced cycloaddition of 2,3-dihydro-2,3-diphenyl-1,4-naphthoquinone (3e) to carbonyl compounds did not occur.The photoinduced cycloadditions of epoxynaphthoquinones to carbonyl compounds are believed to be HOMO-controlled reactions on the basis of substituent effects at the 2- and 3-positions of epoxynaphthoquinones and at the para position of the dipolarophiles, namely, aromatic aldehydes.