US EPA

8463461 

Journal Article 

Photochemistry of Epoxyquinones. 2. Photoinduced Cycloaddition Reactions of Aryl-or Alkyl-Substituted 2,3-Epoxy-2,3-dihydro-1,4-naphthoquinones with Olefins 

Arakawa, S 

1977 

Yes 

Journal of Organic Chemistry
ISSN: 0022-3263
EISSN: 1520-6904 

42 

24 

3800-3811 

English 

10.1021/jo00444a003 

The photochemical reaction of aryl-or alkyl-substituted 2,3-epoxy-2,3-dihydro-1,4-naphthoquinones 1–6 with olefins was examined. Two different photocycloadditions controlled by the substitution pattern of 2,3-substituents have been found. In the photochemical reactions of epoxyquinones 1 and 2 with norbornene, spirooxetanes 7a,b and 8a,b were obtained without ring opening of the oxirane. On the other hand, in the photolysis of epoxyquinones 3–6 with norbornene or N-phenylmaleimide, cycloaddition the 1,3-dipolar type occurred as a result of the internal C-2–C-3 bond fission of epoxyquinones. Upon further irradiation, the photoadducts undergo novel photoisomerization to yield spirophthalides 17–19 involving the 5-oxabicyclo[2.1.1]hexane system and alkylidene phthalides 13–16. The distribution of products depends on the length of irradiation and wavelength of the light source. Substituent effects on these reactions and regioselectivity of the cycloadditions are discussed. A tentative mechanism for these novel photoisomerizations is proposed. © 1977, American Chemical Society. All rights reserved.