A synthetic route to the title ring system is described, which starts from isatoic anhydride and allylamines, and involves as the key step an intramolecular nitrile imine cycloaddition. The simultaneous formation of two new rings, often accompanied by a high degree of regio-and stereo-selectivity, makes the intramolecular 1,3-dipolar cycloadditions an efficient tool for the construction of fused-ring heterocycles.' Our previous contributions in this area deal with intramolecular cycloadditions of nitrile imines, in which however the length of the chain between the reaction centres was such to determine the formation of structures containing a pyrazole unit annulated with a five-or n six-membered ring.L We now wish to describe the application of the same synthetic strategy to the preparation of pyrazolo[1,5-$j[1,4]benzodiazepines. Up to now, very little is reported about this ring system, 334 despite its potential interest in pharmacology in the light of the known biological activity of several hetero-annulated 1,4-benzodiazepines.
RESULTS AND DISCUSSION
The Scheme illustrates the reaction sequence we followed to reach the desired target.
It is to be stressed that the given sequence starts from a trivial compound such as isatoic anhydride, which was reacted with a series of commercially available allylamines (2). This reaction was carried out in anhydrous dimethylformamide and gave the suitably ortho-substituted anilines (31 in good yields with the exception of (3d1, probably because of steric factors. The latter compound was obtained more satisfactorily in an alternative wqY* i.e. by preparation of (4) and its treatment with ally1 bromide in the presence of a