Chiral 1,4‐benzodiazepines. IX . Attempts at a preparation of 7‐chloro‐5‐phenyl‐3( S )methyl‐1,4‐benzodiazepin‐2‐one through C(5)C(5a) bond formation

During attempts at preparation of 7‐chloro‐5‐phenyl‐3( S )methyl‐1,4‐benzodiazepin‐2‐one ( 9 ) by cyclisation of N '‐α‐chlorobenzylidene‐( S )alanyl‐ p ‐chloroaniline ( 7 ) and the related o,p ‐dichloroaniline derivative ( 8 ), it was observed that the intermediate products, both N '‐benzylidene‐( S )alanyl‐ p ‐chloroaniline ( 5 ), as well as the related o,p ‐dichloroaniline derivative ( 6 ), undergo cyclisation to N ‐( p ‐chlorophenyl)‐2‐phenyl‐4( S )methylimidazolidin‐5‐one ( 17 ), and N ‐( o,p ‐dichlorophenyl)imidazolidin‐5‐one ( 18 ), respectively. Isolation and properties of the side products, N '‐benzylated‐( S )alanyl‐ p ‐chloro‐, and o,p ‐dichloroanilines ( 15 and 16 ), as well as of N '‐benzoylated‐( S )alanyl‐ p ‐chloroanilines ( 19 and 20 ) are described.