Synthesis and Photochemistry of β,β′-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 π–π 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. A matter of concentration: The β,β′‐diheteroaryl‐substituted o‐divinylbenzenes 1–3 were irradiated and the photoproducts examined (see scheme): the bisnaphthofuran derivative 3 is the most selective, which, owing to π–π intra‐ or intermolecular complexation, gives only the exo‐bicyclo[3.2.1]octadiene derivative 4 upon irradiation at low concentrations and only the cyclophane derivative 9 at high concentrations.