The product from step 2 above (181 mg, 0.23 mmol) was dissolved in 2 mL of THF and treated sequentially with 37% aqueous formaldehyde (63 μL, 2.30 mmol) and potassium acetate (45 mg, 0.46 mmol) and the mixture stirred for 10 minutes. Sodium triacetoxyborohydride (146 mg, 0.69 mmol) was added and stirring continued for 1.5 hours. The reaction was quenced by the addition of 5 mL of saturated aqueous NaHCO3 and 10 mL of DCM was added. The layers were separated and the aqueous layer was extracted with 10 mL of DCM. The combined organic phases were dried over Na2SO4, filtered and concentrated in vacuo. The residue was purified by column chromatography (ISCO RediSep-4, gradient elution 0%-20% EtOH:acetonitrile). The residue was lyophilized from aqueous acetonitrile to give 85 mg (9% yield) of (S)-3-(3,4-difluorophenyl)-N-(3,3-dimethyl-1-(methylamino)-1-oxobutan-2-yl)-6,6,8-trimethyl-6,7,8,9-tetrahydro-5H-imidazo[1,5-a][1,4]diazepine-1-carboxamide as a white powder. LCMS (+ESI) m/z: 462.3 [MH]+1. 1H-NMR (DMSO d6) δ 8.07 (m, 1H), 7.64-7.48 (m, 3H), 7.35-7.28 (m, 1H), 5.06-4.32 (bs, 2H), 4.24 (d, 1H), 3.91-3.66 (m, 2H), 2.52 (d, 3H), 2.40-2.32 (m, 2H), 2.27 (s, 3H), 1.08 (s, 9H), 0.85 (s, 9H), 0.66 (s, 3H), 0.59 (s, 3H).
