Acid catalysed rearrangement of bis-(p-methoxyphenylcyclopropyl) ketone. Application of X-ray crystallography and nuclear Overhauser effect difference spectra to the structural elucidation of the epimeric hexahydrobenzindenones

When treated with tin(IV) chloride in nitromethane the bis-(p-methoxyphenylcyclopropyl) ketone (2b) rearranged rapidly to a 1 : 1 mixture of epimeric hexahydrobenzindenones (3) and (4). The structure of (3) was determined by X-ray crystallography. Comparison between the nuclear Overhauser effect of difference spectra (NOEDS) of the two products led to the unambiguous assignment of the structure of (4). 1H N.m.r. decoupling experiments provided the evidence that both epimers adopt an identical conformation in solution.