A Cycloaddition-Cyclodehydrogenation Route from Stilbenoids to Extended Aromatic Hydrocarbons

摘要

The photochemical conversion of 2.2'-distyrylhiphenyl (1) both in solution and as a film yields cyclobutane 2 by a stereoselective [2 + 2] cycloaddition. We were interested in preparing a thermally actnc stilbene derivative analogous to 1 not only forsynthetic and mechanistic reasons but also for structuring thin layers. An intramolecular [4 — 2] cxcloadduion would require the previously unknown all-trans-2(4-phenyibu-ta-1,3-dienyl)-2'-styrylbiphenyl (3). We describe here the syrnhe-sis of 3, its thermal cvdizution under mild conditions, to give cyclohexene 4, and the subsequent dehydrugenation affording triplienylene 5 (Scheme 1).