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.