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

Abstract

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.