The Pyrolysis of Phenylnaphthalenedicarboxylic Anhydrides: Products of Ring Contraction and of Radical Cyclization

Abstract

Naphthalene-1,2,-dicarboxylic anhydrides with neighbouring phenyl substituents give on flash vacuum pyrolysis (850-900°/0.02-0.04 mm) ring-contracted carbenes which insert into the phenyl groups. The 8- phenyl anhydride (7) gives acephenanthrylene (10) as the major product, and the 3-phenyl anhydride (15) gives 1,2 : 4,5-dibenzopentalene (indeno [2,1-a]indene) (18). The anhydrides (7) and (15) were   synthesized by pyrolysis of the corresponding 1-naphthylmethyl propynoates (2) and (13) through a new one-step process of intramolecular Diels -Alder addition/retro-Diels -Alder elimination of acetylene.

1-Phenylnaphthalene-2,3-dicarboxylic anhydride (19) on pyrolysis at 960°/0.02 mm gives fluoranthene (11) as the major product. The behaviour of the 1-C₆D₅ compound (24) suggests involvement of a radical cyclization process.