A simple route to 2,3-benzodiazepines from substituted indenes.

Herein, we present a two-step approach for synthesizing 2,3-benzodiazepines from substituted indenes. This process involves oxidation of indenes to 1,5-diketones followed by their cyclocondensation with hydrazine hydrate. The optimized conditions for a wide range of substituted 2,3-benzodiazepines, including the well-known anxiolytic tofisopam, were investigated. A detailed mechanism for the cyclization of 1,5-diketones with hydrazine hydrate was established using 1H NMR kinetic experiments.