A New Route to Polycondensed Aromatics: Photolytic Formation of Triphenylene and Dibenzo[fg,op]naphthacene Ring Systems

Application of photo-aryl coupling reactions for the syntheses of triphenylene and dibenzo[fg,op]naphthacene was explored. Three types of reactions were developed: Photocyclodehydrogenation of polyphenyl compounds, photolytic reactions of iodoarenes, and photocyclodehydrohalogenation of halogenopolyaryls. The effects of solvent, oxidant, and wavelength on the photocyclization of o-terphenyl and 2,2′-diphenylbiphenyl to the triphenylene and naphthacene, respectively, were examined. The conversion was best achieved by the reaction carried out in an aromatic solvent in the presence of an equimolar amount of iodine using a quartz or a Vycor vessel. Versatility of the processes was shown by the formation of naphthacene starting from either 2,2′-diphenyl-biphenyl (57% yield), 2,2′-bis(2-chlorophenyl)biphenyl (67%), 1,2,3-triphenylbenzene (21%), or 2,6-diiodo-biphenyl.