Conformational studies of helicenes—VIII1: Synthesis and conformation of two hexahelicene analogues having a non-aromatic, five-membered ring

Abstract Phenanthro[3,4-c]fluorenone ( 5 ) and phenanthro[3,4-c]fluorene ( 1 ) have been prepared from hexahelicene-5,6-quinone. The effect of the presence of a five-membered ring on the helical conformation has been studied by comparison of NMR data of 1 and 5 with those of hexahelicene. Force field calculations of the structure of 1 agree with the results of the NMR analysis.