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

A study of the photochemistry of the title 9-chloromethyldibenzobarrel ene-11,12-diester (1) reveals the formation of semibullvalene derivati ves [(2) and (3)] in acetone solution, with additional noveL photoprod ucts [two isomers of dimethyl trahydroindeno[2,1-a]-indene-5a,10a-dica rboxylate; (4) and (5)] in other solvents, and especially in solid-sta te photolysis. The structures of (1), (4) and (5) have been determined by X-ray crystal analyses. Crystal data: T = 294 K, Cu Kalpha, lambda = 1.5418 angstrom, C21H17ClO4, M(r) = 368.82. (1), monoclinic, P2(1)/ c, a = 10.087 (1), b = 16.207 (1), c = 11.233 (1) angstrom, beta = 107 .64 (1)-degrees, V = 1749.9 (2) angstrom3, Z = 4, D(x) = 1.400 g cm-3, F(000) = 768, mu = 24.4 cm-1 R = 0.042 for 2569 reflections. (4), tri clinic, P1BAR, a = 13.893(1), b = 15.968 (2), c = 8.191 (2) angstrom, alpha = 98.13 (2), beta = 91.78 (2), gamma = 99.54 (1)-degrees, V = 17 71.2 (4) angstrom3, Z = 4 (two molecules per asymmetric unit), D(x) = 1.383 g cm-3, mu = 21.2 cm-1, R = 0.045 for 5645 reflections. (5) [15% (4) as impurity], mono-clinic, P2(1)/c, a = 14.777 (1), b = 8.581 (1) , c = 15.192 (1) angstrom, beta = 112.10 (1)-degrees, V = 1784.8 (3) a ngstrom3, Z = 4, D(x) = 1.372 g cm-3, F(000) = 768, mu = 21.0 cm-1, R = 0. 103 for 2874 reflections. Photolysis of (1) in acetone results in the formation, via the triplet excited state, of the normal di-pi-met hane photoproducts (2) and (3). In other solvents and in the solid sta te, photolysis, via the singlet excited state, results in the novel di benzopentalenes, (4) and (5); the mechanism by which these products ar e formed probably involves photorearrangement via a biradical (6), fol lowed by a non-concerted Cl-atom migration. Solid-state photolysis pro duces relatively larger amounts of (4) and (5), and this information m ay be correlated with a favorable intermolecular C ... Cl contact of 4 .28 angstrom in the crystal structure of (1).