Diisobutylaluminumhydride → tert-butyl N-[(2S)-4-oxobutan-2-yl]carbamate

1,1-Dimethylethyl[(1S)-1-methyl-3-oxopropyl]carbamate. To a stirred solution of 1,1-dimethylethyl[(1S)-2-cyano-1-methylethyl]carbamate (0.656 g, 3.56 mmol) in anhydrous ether cooled to −4.0° C. was added dropwise a 1.0 M solution of diisobutylaluminum hydride in hexanes (14.2 mL, 14.2 mmol) over 20 minutes. Stirring was continued at this temperature for an additional 20 minutes. The yellow solution was quenched with Rochelle's salt and the resultant stirred at room temperature for 1 hour. The solids were filtered off through celite and rinsed with EtOAc. The organics were washed with brine, concentrated, and flash chromatographed (10-100% EtOAc/hexanes) to give 1,1-dimethylethyl [(1S)-1-methyl-3-oxopropyl]carbamate (0.193 g, 30%) as a clear oil. 1H NMR (400 MHz, CDCl3) δ 1.22 (d, J=6.8 Hz, 3H), 1.41 (s, 9H), 2.53-2.65 (m, 2H), 4.08-4.13 (m, 1H), 4.63 (m, 1H), 9.74-9.75 (m, 1H). b) 1,1-Dimethylethyl[(1S)-3-(cyclopropylamino)-1-methylpropyl]carbamate. The protected diamine was prepared using a modified procedure as described in example Z-32. A solution of 1,1-dimethylethyl[(1S)-1-methyl-3-oxopropyl]carbamate (0.178 g, 0.95 mmol) and cyclopropylamine (197 μL, 2.85 mmol) in anhydrous dichloroethane (10 mL) was treated with acetic acid (272 μL, 4.8 mmol) and stirred for 30 minutes. Sodium triacetoxyborohydride (0.444 g, 2.1 mmol) was added and the solution was stirred for 20 hours. The resultant was subjected to a workup and purification procedure as described in example Z-32 to give 1,1-dimethylethyl [(1S)-3-(cyclopropylamino)-1-methylpropyl]carbamate (0.136 g, 63%) as a clear oil. 1H NMR (400 MHz, CDCl3) δ 0.32-0.42 (m, 4H), 1.12 (d, J=6.8 Hz, 3H), 1.89-1.51 (m, 10H), 1.58-1.02 (m, 2H), 2.05-2.10 (m, 1H), 2.67-2.80 (m, 2H), 3.71 (m, 1H), 4.78 (m, 1H). c) [(33)-3-Aminobutyl]cyclopropylamine dihydrochloride was prepared in a similar manner as described in example Z-20, 1H NMR (400 MHz, CDCl3/CD3OD) δ 0.70-0.75 (m, 2H), 0.90-0.94 (m, 2H), 1.18 (d, J=6.8 Hz, 3H), 1.84-1.94 (m, 1H), 1.97-2.05 (m, 1H), 2.40-2.54 (m, 1H), 2.99-3.04 (m, 2H), 3.23-3.28 (m, 1H). d) (4S,12aS)-1-Cyclopropyl-N-[(2,4-difluorophenyl)methyl]-7-hydroxy-4-methyl-6,8-dioxo-1,2,3,4,6,8,12,12a-octahydropyrido[1′,2′:4,5]pyrazino[1,2-a]pyrimidine-9-carboxamide. The title compound was made in two steps using a similar process to that described in example Z-2. 16a (80 mg, 0.17 mmol) and free based [(3S)-3-aminobutyl]cyclopropylamine (75 mg, 0.59 mmol) were reacted in dichloromethane (2 mL) with acetic acid to give (4S,12aS)-1-cyclopropyl-N-[(2,4-difluorophenyl)methyl]-4-methyl-6,8-dioxo-7-[(phenyl methyl)oxy]-1,2,3,4,6,8,12,12a-octahydropyrido[1′,2′:4,5]pyrazino[1,2-a]pyrimidine-9-carboxamide (74 mg, 80%) as a film. This material was hydrogenated in a second step as described in example Z-2 to give (4S,12aS)-1-cyclopropyl-N-[(2,4-difluorophenyl)methyl]-7-hydroxy-4-methyl-6,8-dioxo-1,2,3,4,6,8,12,12a-octahydropyrido[1′,2′:4,5]pyrazino[1,2-a]pyrimidine-9-carboxamide (32 mg, 52%) as an off-white solid, 1H NMR (400 MHz, CDCl3) δ 0.37-0.54 (m, 3H), 0.64-0.70 (m, 1H), 1.35 (d, J=7.2 Hz, 3H), 1.45-1.49 (m, 1H), 1.76-1.80 (m, 1H), 2.03-2.12 (m, 1H), 2.86-2.93 (m, 1H), 2.99-3.04 (m, 1H), 4.30 (dd, J=4.0, 13.6 Hz, 1H), 4.49-4.67 (m, 4H), 5.00-5.07 (m, 1H), 6.75-6.82 (m, 2H), 7.32-7.36 (m, 1H), 8.28 (s, 1H), 10.49 (m, 12.53 (s, 1H); ES+ MS; 459 (M+1).