Structure of dinaphtho[2,1-b:1,2'-d]-five-membered ring aromatic heterocycles

A comparison between the X-ray structures of a series of binaphthyl-substituted five-membered aromatic heterocycles la-e, comprising pyrrole, furan, phosphole, thiophene and others, enlightens the effect of the heteroatom on the distortion of the molecules and the differences with the fully aromatic helicene, If (dibenzophenanth'ene). The X-ray data were either taken from the literature (le, le and If) or from compounds prepared in the course of the present study (la and Id). The furan Ib has also been prepared by new methods but its crystals were not suitable for X-ray analysis. The X-ray structures of the tetrahydro-substituted nitrogen and oxygen heterocycles 2a and 2b are also reported. The energy barrier to racemization has been determ ned by line-shape analysis of VT-NMR spectra for those.molecules where the presence of a substituent at the heteroatom and a high pyramidal inversion barrier render the naphthyl protons at the 1 and 13 position non equivalent (i.e. in le, Id', and Id").