The photochemistry of 6- and 7-cyano-2,3-benzobicyclo[4.2.0]octa-2,4,7-triene

Abstract

The direct irradiation of 7-cyanobenzocyclooctatetraene (5) led to 6- and 7-cyano-2,3-benzobicyclo[4.2.0]octa-2,4,7-triene (7 and 8; Φ7 = Φ8 < 0.0001). On direct irradiation, 7 gave 1-cyanobenzosemibullvalene (6; Φ = 0.19), 5 (Φ = 0.022), and 2-cyanonaphthalene (Φ = 0.04), whereas 8 gave 7-cyanobenzosemibullvalene (16; Φ = 0.03), 5 (Φ = 0.22), naphthalene (Φ = 0.12), and 4-cyano-7,8-benzotetracyclo[3.3.0.02,4.03,6]oct-7-ene (17, Φ = 0.03). Upon sensitized irradiation, 7 gave 6 (Φ = 0.68) and 2-cyanonaphthalene (Φ = 0.007), while 8 gave 16 (Φ = 0.01) and naphthalene (Φ = 0.52). Deuterium labelling studies suggest that 6 and 16 derive from Zimmerman di-π-methane rearrangements.