EFFECT OF THROUGH-SPACE INTERACTION ON THE PHOTOLYTIC DESULFURIZATION OR DESELENIZATION AND INTRAMOLECULAR CYCLIZATION REACTIONS OF 1,9-DISUBSTITUTED DIBENZOCHALCOGENOPHENES

1,9-Dithia and 1,9-diselena substituents in dibenzochalcogenophenes 1 are in close proximity within the van der Waals S-S and Se-Se contacts and hence have a strong through-space interaction. Photolysis of the compounds 1 with a 400 W high-pressure mercury lamp in benzene produces triphenyleno[4,5-bcd]chalcogenophenes 2 and tribenzo[bc,e,hi][2,7]dichalcogenaazulenes 3 in high yields, except for the dibenzofuran derivative, via photoexcitation, sequential desulfurization or deselenization, and intramolecular cyclization. In the reaction, 1,9-bis(phenylthio)dibenzofuran (1e) exhibits lower reactivity as compared with other dibenzothiophene and dibenzoselenophene derivatives. The X-ray crystallographic analysis of 1,9-bis(phenylseleno)dibenzoselenaphene (1a), 1,9-bis(phenylseleno)dibenzothiophene (1b), and 1,9-bis(phenylthio)dibenzoselenophene (1c) demonstrated that; their structures are distorted as is also that of 1,9-bis(phenylthio)dibenzothiophene (1d),(1) while dibenzofuran derivative 1e was found to be a nearly planar molecule. The structure and reactivity relationship of compounds 1a-e was examined in the photolytic reactions by comparing their interheteroatomic distances at the 1,9 positions and their oxidation potentials. Furthermore, compounds 1a-e afforded the corresponding monosulfoxides and bis-sulfoxides on oxidation with m-chloroperbenzoic acid which were photolyzed readily to give also 2 and 3.