ON THE SYNTHESIS OF HEXAMETHOXYPHENANTHRENES - AN EFFICIENT PHENANTHRENE SYNTHESIS VIA INTRAMOLECULAR OXIDATIVE CYCLIZATION OF 2,2'-DIHYDRAZONYLBIPHENYLS
Mz. Cherkaoui et G. Scherowsky, ON THE SYNTHESIS OF HEXAMETHOXYPHENANTHRENES - AN EFFICIENT PHENANTHRENE SYNTHESIS VIA INTRAMOLECULAR OXIDATIVE CYCLIZATION OF 2,2'-DIHYDRAZONYLBIPHENYLS, New journal of chemistry, 21(11), 1997, pp. 1203-1210
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.