A Stereospecific `2‐Aza‐divinylcyclopropane' Rearrangement

Abstract The stereochemical course of the thermal 2‐aza‐ Cope rearrangement of the optically pure acyl azide (−)‐(1 S )‐ 5 was investigated by determination of the absolute configuration of the rearrangement product (1 R ,8 S )‐ 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.