A Serendipitous Synthesis of 11a-Hydroxy-11,11a-dihydrobenzo[e]indeno[2,1-b][1,4]diazepine-10,12-dione Derivatives by Condensation of 2-Aminobenzamides with Ninhydrin in Water.

Ninhydrin undergoes an unprecedented condensation reaction with various 2-aminobenzamide derivatives in boiling water to afford 11a-hydroxy-11,11a-dihydrobenzo[e]indeno[2,1-b][1,4]diazepine-10,12-dione derivatives. These hitherto unreported products are easily isolated in high yield by a simple filtration step. An interesting "ortho effect" was observed in the condensation reaction of ninhydrin with 2-amino-N-phenylbenzamide derivatives having an ortho- substituent in the N-phenyl moiety wherein the corresponding expected 3'-phenyl-1'H-spiro[indene-2,2'-quinazoline]-1,3,4'(3'H)-triones were obtained.