Reactions of 2,3‐dihydro‐1H‐1,5‐benzodiazepines and chloroacetyl chlorides: Synthesis of 2a,3,4,5‐tetrahydro‐azeto [1,2‐a][1,5] benzodiazepin‐1(2H)‐ones

2a,4‐Disubstituted 5‐benzoyl‐2‐chloro/2,2‐dichloro‐2a,3,4,5‐tetrahydro‐azeto [1,2‐a] [1,5]benzodiazepin‐1 (2H)‐ones ( 3a–h ) were synthesized by cycloaddition reactions of 2,4‐disubstituted 1‐benzoyl‐2,3‐dihydr o‐1H‐1,5‐benzodiazepines ( 2a–h ) and ketenes, generated from chloroacetyl chloride or dichloroacetyl chloride in the presence of triethylamine, in anhydrous benzene. In some cases, ring contraction of benzodiazepines has also been observed. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:636–640, 2001