Studies of bridged benzo-heterocycles. Part II. Cycloaddition reactions of epoxy-bridged cyclic olefins with tropone and tropolone, and photochemical behaviour of the adducts

Abstract

Reactions of 1,4-epoxy-1,4-dihydronaphthalene (I) with tropone and tropolone gave rise to the [4 + 2]π endo,exo-(IIIa), and exo,exo-(Vb) cycloadducts, respectively, in relatively high yield; reactions of dimethyl 7-oxabicyclo-[2,2,1]hepta-2,5-diene-2,3-dicarboxylate (II) with tropone and tropolone afforded the [4 + 2]π endo,exo(VIIa), and endo,exo- cycloadducts (VIIb), respectively, in comparatively low yields. Irradiations of the tropone adducts (IIIa) and (VIIa) in methanol gave exclusively the methyl 12-oxatetracyclo[7,2,1,0^2,8,0^3,5]dodecadien-4-ylacetates (XIIa and b). Similar irradiations of the tropolone adducts (Vb) and (VIIb) give the 14-oxotetracyclo [9,2,1,0^2,10,0^3,7]tetradecadien-6,9-diones (XV) and (XVII), respectively, each being the only product. The photoproducts (XIIa and b) are formed by addition of methanol to initially formed ketens, and the photoproducts (XV) and (XVII) by [1,3] sigmatropic rearrangements of (Vb) and (VIIb), respectively, followed by hydrogen shifts.