Dimethyl 4b,8b,8c,8d-tetrahydro-dibenzo[a,f]cyclopropa[cd]pentalene-8b-carboxylat e-8c-thionocarboxylate and the corresponding 8c-thiolocarboxylate

The title compounds, methyl 8c-[methoxy(thiocarbonyl)]-4b,8b,8c,8d-tetrahydrodibenzo [a,f]cyclo-propa [cd] pentalene-8b-carboxylate, C20H16O3S, and methyl 8c-[(methylthio)]carbonyl-4b,8b,8c,8d-tetrahydrodibenzo [a,f]cyclopropa[cd]pentalene-8b-carboxylate, C20H16O3S, are the photoproducts in the photolysis of the dibenzobarrelene thiono and thiolo esters, The geometry and dimensions of the molecules are similar to those of related materials. Only one photoproduct (of two possible) is formed in each case, with initial vinyl-benzo bond formation involving the vinyl C atom carrying the non-thioester group; intermediate biradicals are stabilized by resonance interaction with the thioester groups.