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.