The beckmann rearrangement of cyclohex‐2‐enone oximes. Synthesis of 4,5‐diphenyl‐2,3,4,5‐tetrahydro‐1H‐azepin‐2‐one

Abstract The Beckmann rearrangement of either syn or anti 3,4‐diphenyl‐cyclohexenone oxime 2a,b in polyphosphoric acid produces only one of the two possible isomeric unsaturated caprolactams 1 . Under neutral conditions, only the syn oxime tosylate 9b rearranges to lactam 1 , the anti oxime tosylate 9a remains unchanged. These results support earlier reports that alkyl migration is preferred over vinyl migration in the Beckmann rearrangement of unsaturated cyclic ketoximes. Structure proof of the lactam was made using deuterium exchange and HMQC nmr experiments.