Hydrogen Bromide → 3(R,S)-amino-5-cyclohexyl-1,3-dihydro-1-methyl-2H-1,4-benzodiazepin-2-one

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A mixture of 3(R,S)-[(benzyloxycarbonyl)amino]-5-cyclohexyl-1,3-dihydro-1-methyl-2H-1,4-benzodiazepin-2-one (3.0 g) and hydrobromic acid (45% in acetic acid; 6.2 ml) was stirred for 1 hour at room temperature under a nitrogen atmosphere. The mixture was then diluted with cold anhydrous diethyl ether (40 ml) and it was stirred at 0° C. for 45 minutes. The white precipitate was collected by filtration, washed with cold diethyl ether (4×30 ml) and then dissolved in a mixture of water (30 ml) and 2N sodium hydroxide (15 ml). The basic aqueous phase was extracted with ethyl acetate (3×70 ml) and the combined organic solutions were washed with brine (1×30 ml), dried (Na2SO4) and concentrated. Flash chromatography of the remaining pale red oil (silica gel, dichloromethane-methanol, 94:6) gave the title compound (1.6 g) as a waxy solid; δH (250 MHz, CDCl3) 7.53-7.45 (2H, m), 7.28-7.20 (2H, m), 4.30 (1H, s), 3.39 (3H, s), 2.75 (1H, m), 2.04-1.03 (10H, m); m/z (CI) 272 (M+ +1).

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