The Photochemistry of 7,8-Dimethylene-1,3,5-cyclooctatrienes. the Synthesis of Bicyclo[6.2.0]deca-1,3,5,7-tetraene

Abstract

Ultraviolet irradiation of 7,8-dimethylene-1,3,5-cyclooctatriene (1) led to bicyclo[6.2.0]deca-1,3,5,7-tetraene (4). Irradiation of 7-methylene-8-bromomethylene-1,3,5-cyclooctatriene (2) also gave 4, as well as 5- (or 6-) methylene-6- (or -5-) bromomethylenetricyclo[5.1.0.04,8]oct-2-ene (10). Similar irradiation of 7-methylene-8-chloromethylene-1,3,5-cyclooctatriene (3) yielded 5- (or 6-) methylene-6- (or -5-) chloromethylenetricyclo[5.1.0.04,8]-oct-2-ene (11) as well as 4- (or 5-) methylene-5- (or -4-) chloromethylene-cis-bicyclo[4.2.0]octa-2,7-diene (12). The structures 4, 11, and 12 were confirmed by catalytic hydrogenation. Diels-Alder reaction of 11 with dimethyl acetylenedicarboxylate led to dimethyl 2,3-benzotricyclo[5.1.0.04,8]octa-2,5-diene-10,11-dicarboxylate (19), a benzfused derivative of semibullvalene (20). Similar Diels–Alder reaction of 12 with dimethyl acetylenedicarboxylate yielded a ca. 1:1 mixture of dimethyl 2,3-benzo-cis-bicyclo[4.2.0]octa-2,4,7-triene-10,11-dicarboxylate (22) and dimethyl benzocyclooctatetraene-10,11-dicarboxylate (23). Heating the mixture of 22 and 23 at 120° resulted in the complete conversion of 22 to 23. Show more