Formation of Cyclopent[hi]acephenanthrylene From 1,2-, 1,3-, 1,4- and 2,3-Triphenylenedicarboxylic Acid Derivatives on Flash Vacuum Pyrolysis at >900°C

Abstract

The processes involved in the conversion of triphenylene , C₁₈H₁₂, into cyclopent [hi] acephenanthrylene, C₁₈H₁₀, under flash vacuum pyrolytic conditions at 900-1100°C have been investigated by pyrolysing triphenylene-1,2- and -2,3-dicarboxylic anhydrides and diallyl triphenylene-1,3- and -1,4-dicarboxylates to give the corresponding didehydrotriphenylenes in the gas phase. These didehydro intermediates are converted into mixtures of cyclopent [hi] acephenanthrylene and triphenylene in different yields and proportions. Pyrolysis of 9,10-diethynylphenanthrene. C₁₈H₁₀, yields cyclopent [hi] acephenanthrylene in good yield. Pyrolysis of 1-nitrotriphenylene and allyl triphenylene-2-carboxylate to give the triphenylen-1-yl and -2-yl radicals leads to formation of the same products. Mechanisms involving radical rearrangements (C₁₈H₁₁ species) and benzyne-cyclopentadienylidenecarbene and ethyne-ethenylidene rearrangements (C₁₈H₁₀ species) are discussed.