Stereoselective Intramolecular Cycloadditions of Homochiral Nitrile Imines: Synthesis of Enantiomerically Pure 3,3a-dihydro-pyrazolo[1,5-a][1,4]benzodiazepine-6(4H)-ones

Starting from the commercially available (S)-1-phenylethylamine, we have synthesised the homochiral hydrazonoyl chlorides 4. The intramolecular cycloaddition of the corresponding nitrile imines 5 gave the diastereoisomeric 3,3a-dihydro-pyrazolo[1,5-a][1,4]benzodiazepine-6(4H)-ones 6 and 7 in enantiopure form.