A Stereospecific `2-Aza-divinylcyclopropane' Rearrangement

Abstract

The stereochemical course of the thermal 2-aza-Cope rearrangement of the optically pure acyl azide (−)-(1S)-5 was investigated by determination of the absolute configuration of the rearrangement product (1R,8S)-9. The reaction proceeds by a sequence of stereospecific steps from 5 to an equilibrating mixture of exo- and endo-isocyanates 6 and 7. The endo-isomer 7 undergoes Cope rearrangement to the putative intermediate 8, which is trapped and characterized as the adduct 9b of butan-1-ol. The absolute configuration of 9b was determined by its reduction to the amide 20, and determination of the X-ray structure of the N-camphanoylamide 21 derived from camphanic acid of known absolute configuration.