ON THE SYNTHESIS OF HEXAMETHOXYPHENANTHRENES - AN EFFICIENT PHENANTHRENE SYNTHESIS VIA INTRAMOLECULAR OXIDATIVE CYCLIZATION OF 2,2'-DIHYDRAZONYLBIPHENYLS

Successful intramolecular cyclization of hexamethoxybiphenyls to their phenanthrene analogs is discussed. Thus treatment of 2,2'-bis(bromome thyl)hexamethoxybiphenyl with triphenylphosphine in the presence of ba se gave the phenanthrene derivative in yields of up to 20%. Based on a reaction mechanism including intramolecular dimerization of biphenyl- 2, 2'-dicarbene, a dihydrazone was synthesized from 2,2'-diformylhexam ethoxybiphenyl, the first isolated example of dihydrazones of this typ e. Subsequent oxidation by a solution of copper(l) chloride in pyridin e and molecular oxygen gave the hexamethoxyphenanthrenes in yields of up to 90%. Such intramolecular dimerization of the dicarbene of biphen yl compounds is observed for the first time. Highly substituted phenan threnes may thus be obtained in four to six steps.