To a suspension of (3aR*,10aS*)-9-(4-aminobenzyl)-4-(phthalimidoacetyl)-2,3,3a,4,9,10a-hexahydrobenzo[b]cyclopenta[e][1,4]diazepin-10(1H)-one (198 mg, 0.4 mmol) in chloroform (2 mL)-methanol (2 mL) was added benzaldehyde (49 μL, 0.48 mmol) and the mixture was stirred at room temperature for 40 minutes. To the resulting solution was added bromocresol green as well as sodium cyanoborohydride (30 mg, 0.48 mmol). Then, 10% HCl/methanol was added dropwise until the color of the mixture had ceased to change. This reaction mixture was stirred at room temperature for 15 minutes, at the end of which time it was diluted with water and extracted with 3 portions of chloroform. The pooled organic layer was washed with water, dried over MgSO4, filtered, and concentrated under reduced pressure. The residue was crystallized from ethanol to provide 163 mg (Yield 70%) of the title compound. m.p. 178°-182° C.
