Curtius rearrangement in the 5-phenyl-1,4-benzodiazepine series. Unprecedented participation by an imine nitrogen

The previously unknown 3-aminomethyl-1,3-dihydro-5-(2′-fluorophenyl)-2H,4-benzodiazepin-2-one, 3a, was synthesized in two steps as a racemate. In the chiral series, 3(S)-azidocarbonylmethyl-1,3-dihydro-5-phenyl-2H-1,4-benzodiazepin-2-one, 12b, was prepared from Nα-Cbz-β-methylaspartate in five synthetic operations and subjected to Curtius rearrangement. The intermediate isocyanate was trapped intramolecularly by the 5-imine nitrogen of the benzodiazepine ring in 12b. This unanticipated result runs counter to the generally held dictum that the isocyanate group has a strictly linear shape.