Synthesis and structures of diindeno-fused 1,12-diphenylbenzo[c]phenanthrene and 1,14-diphenyl[5]helicene bearing severe helical twists

Diindeno-fused 1,12-diphenylbenzo[c]phenanthrene 15 and 1,14-diphenyl[5]helicene 20 were prepared in a four-step synthetic sequence from 2,7-naphthalenedicarboxylic acid and 3,6-phenanthrenedicarboxylic acid, respectively. The X-ray structures of 15 and 20 show that the fused ring systems possess severe helical twists. The rotational barriers of the phenyl substituents were determined by the analysis of temperature-dependent 1H NMR spectra. [structure: see text]