Nuclear magnetic resonance studies of heterocyclic bridged biphenyls

Abstract

Condensation reactions (a) between 1,2-diamines and biphenyl-2,2′-dicarbaldehyde or 9,10-phenanthraquinone and (b) between 2,2′-diaminobiphenyl and 1,2-diketones give polycyclic products with 5-, 6-, 7- and 8-membered heterocyclic rings, the n.m.r. spectra of which are discussed. Temperature-dependent signals for the methylene protons in the 15H-dibenzo[c,e]benzimidazo[1,2-a]azepines (2) and (3) show that these compounds are conformationally labile. The dibenzo[a,c]phenazines (4) and (5) and dibenzo[f,h]quinoxaline (6) show large downfield shifts (δca. 9·5) for some aromatic protons.