Synthesis and photochemistry of beta,beta'-di(2-furyl)-substituted o-divinylbenzenes: intra- and/or intermolecular cycloaddition as an effect of annelation.

New heteroaryl-substituted o-divinylbenzenes, 2,2'-(1,2-phenylenedivinylene)difuran (9), 2,2'-(1,2-phenylenedivinylene)bisbenzo[b]furan (10), and 2,2'-(1,2-phenylenedivinylene)bisnaphtho[2,1-b]furan (11), were prepared and irradiated at various concentrations; intramolecular photocycloaddition and intermolecular [2+2] twofold photoaddition reactions took place to give bicyclo[3.2.1]octadiene derivatives 12-14 and cyclophane derivatives 15-17, respectively. Compound 11 was the most selective of these o-divinylbenzenes, which, owing to pi-pi intra- or intermolecular complexation, gave only the exo-bicyclo[3.2.1]octadiene derivative 14 at low concentrations, and only the cyclophane derivative 17 at high concentrations.