Flash Vacuum Pyrolysis of Phenanthrene-3,4-dicarboxylic Anhydride and of Cyclobuta[c]-phenanthrene-1,2-dione: Products of Ring Contraction, Insertion and Ring Cleavage

Abstract

Flash vacuum pyrolysis of phenanthrene-3,4-dicarboxylic anhydride and of cyclobuta [c]phenanthrene-1,2-dione (860-70°/0.02-0.04 mm) gave a pyrolysate containing 1-ethynylacenaphthylene, 3-ethynylacenaphthylene and phenanthrene. The identity of the two ethynes was confirmed by synthesis. The results are interpreted in terms of a reaction sequence involving aryne formation, ring contraction, carbene insertion and ring cleavage of a highly strained intermediate.