A Study of the Photochemistry of Benzobicyclo[2.2.2]octan-2-ones

Abstract

The anti- and syn-3-methyl isomers of 5,8-dimethoxy-1,3-dimethyl-3,4-dihydro-1,4-ethanonaphthalen-2(1H)-one (2) and (3) and the 1,3,3- trimethyl analogue (4) were prepared from the Diels -Alder adduct of benzoquinone and 1,3-dimethylcyclohexadiene. The photochemistry of each has been studied and the structures of several photoproducts have been assigned. One of the products from irradiation of (3) was found by X-ray analysis to be a 1,4-disubstituted 1,2,3,4- tetrahydronaphthalene [methyl 2-(5′,8′-dimethoxy-4z′-methyl-1′,2′,3′,4′-tetrahydronaphthalen-1′-yl) propanoate ] with the unexpected cis-stereochemistry (11). Irradiation of (4) produces, inter alia, a compound containing the unusual tetracyclo [7.4.0.0^2,7.0^4,8] trideca -1(9),10,12-triene skeleton whose structure was determined by n.m.r. spectroscopy.