Photochemistry of 4-Cyano-2,3-benzobicycloocta-2,4,7-triene

Article abstract of DOI:10.1021/jo00017a007

4-Cyano-2,3-benzobicyclo<4.2.0>octa-2,4,7-triene (11) was found to be thermally and photochemically reactive.Heating solutions of 11 at 150 deg C for 2 h gave 5-cyanobenzocyclooctatetraene (10) quantitatively.The direct irradiation of triene 11 gave 2-cyanobenzosemibullvalene (i.e., SB 12, 63percent, Φ = 0.067), COT 10 (28percent, Φ = 0.031), and 1-cyanonaphthalene (ca. 0.5percent, Φ = 0.0005).Upon sensitization with p-(dimethylamino)benzophenone, 11 gave 12 (30percent, Φ = 0.028), COT 10 (9percent, Φ = 0.0093), and 1-cyanonaphthalene (2percent, Φ = 0.0018).Studies with deuterium-labeled triene (11a) revealed that semibullvalene produced from direct irradiation possessed a different label distribution to that obtained from sensitized irradiation, and hence state-dependent pathways operate in the SB formation.The mechanism proposed for the SB formation from S1 of 11 involves a 1,2-shift with cleavage of the cyclobutene C1-C6 bond of the triene, while SB formation from T1 results from a Zimmermann di-?-methane rearrangement.