CRYSTAL-STRUCTURE CORRELATIONS IN THE PHOTOCHEMISTRY OF DIMETHYL 9-PHENYL-9,10-DIHYDRO-9,10-ETHENOANTHRACENE-11,12-DICARBOXYLATE

A study of the photochemistry of the title 9-phenyl-dibenzobarrelene-11,12-diester (1) reveals the formation of a semibullvalene derivative, dimethyl 8b-phenyl-4b,8b,8c,8d-tetrahydrodibenzo[a,f]cyclopropa[cd]pentalene-8c,8d-dicarboxylate (2), in acetone solution, with an additional cyclooctatetraene (COT) photoproduct, dimethyl 5-phenyldibenzo[a,e]cyclooctene-6,12-dicarboxylate (3), in acetonitrile, benzene and in solid-state photolysis. Crystal data: T = 294 K, Cu Kalpha, lambda = 1.5418 angstrom, C26H20O4, M(r) = 396.44. (1), triclinic, P1BAR, a = 10.713 (1), b = 11.991 (1), c = 8.177 (1) angstrom, a = 95.71 (1), beta = 105.14 (1), gamma = 79.61 (1)degrees, V = 995.9 (2) angstrom3, Z = 2, D(x) = 1.322 g cm-3, F(000) = 416, mu = 6.8 cm-1, R = 0.060 for 3069 reflections. (2), monoclinic, P2(1)/n, a = 10.206 (3), b = 16.485 (1), c = 11.758 (4) angstrom, beta = 95.48 (2)degrees, V = 1969.2 (8) angstrom3, Z = 4, D(x) = 1.337 g cm-3, F(000) = 832, mu = 6.9 cm-1, R = 0.039 for 2882 reflections. (3), triclinic, P1BAR, a = 11.074 (2), b = 25.298 (6), c = 7.668 (2) angstrom, alpha = 94.22 (2), beta = 94.53 (2), gamma = 101.77 (2)degrees, V = 2087.5 (8) angstrom3, Z = 4 (two molecules per asymmetric unit), D(x) = 1.261 g cm-3, F(000) = 832, mu = 6.5 cm-1, R = 0.039 for 4668 reflections. Compound (2) has a structure consistent with formation via normal di-pi-methane reaction involving the triplet excited state, while formation of (3) provides another example of unexpected behaviour of the singlet excited state.