Synthesis of a strained, air-sensitive, polycyclic aromatic hydrocarbon by means of a new 1,4-benzadiyne equivalent

9,11,20,22-Tetraphenyltetrabenzo[a,c,l,n]pentacene (4) was prepared by the pyrolysis of 1,4-bis(phenyliodonio)benzene-2,5-dicarboxylate (9), a new 1,4-benzadiyne equivalent, in the presence of phencyclone. Although stable as a solid, solutions of 4 must be handled in the dark; otherwise, ambient light promotes its oxygenation to the 10,21-endoperoxide (10). The X-ray structures of both 4 and 10 were determined, as well as the stuctures of two dihydrophencyclones isolated as byproducts of the pyrolysis. Compound 4 adopts a conformation with approximate C-2h symmetry in the solid state, in contrast to the results of gas-phase calculations, which uniformly predict a twisted, D-2-symmetric ground state structure. (C) 2002 Elsevier Science Ltd. All rights reserved.