Photochemistry of Dimethyl 1,8-Dichloro-9,10-dihydro-9,10-ethenoanthracene-11,12-dicarboxylate

The molecule of the title compound, (1), C 20 H 14 Cl 2 O 4 , has geometry and dimensions similar to those of related materials ; one ester group is fully conjugated with the C=C double bond and the other is non-conjugated. Photolysis of (1) produces two dibenzosemibullvalenes, the reaction being controlled mainly by intramolecular steric effects of the Cl substituents.