Formation of Cyclopent[a]indene and Acenaphthylene from Allyl Esters of Biphenyl Mono- and Di-carboxylic Acids and from Biphenyl Dicarboxylic Anhydrides on Flash Vacuum Pyrolysis at 1000–1100°C

Abstract

Flash vacuum pyrolysis at 1000-1100°C of the allyl esters of the three isomeric biphenylcarboxylic acids, of the allyl esters of the 12 biphenyldicarboxylic acids and of the three biphenyldicarboxylic anhydrides gave pyrolysates which were examined by ¹H n.m.r. spectroscopy at temperatures below -50°C. In all cases the spectra showed the presence of cyclopent[a]indene and acenaphthylene together with other products. Possible mechanisms for these ring contraction and cyclization processes are discussed and the results of pyrolyses of [2,3-¹³C₂] biphenyl-2,3-dicarboxylic anhydride, and [3,4-¹³C₂]- and (2-² H₁)-biphenyl-3,4-dicarboxylic anhydrides are reported.