Ammonium formate → tert-butyl 7-(4-hydroxy-2-oxopyridin-1(2H)-yl)-5-methyl-3,4-dihydro-1H-pyrido[4,3-b]indole-2(5H)-carboxylate

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To a solution of tert-butyl 7-(4-(benzyloxy)-2-oxopyridin-1(2H)-yl)-5-methyl-3,4-dihydro-1H-pyrido[4,3-b]indole-2(5H)-carboxylate (0.98 g, 2.0 mmol) in CH3OH (30 mL) was added 5% Pd/C (0.3 g) and ammonium formate (0.32 g, 5.1 mmol) under an atmosphere of argon. The reaction was stirred at 90° C. until complete. The reaction mixture was cooled and filtered through a layer of Celite. The solvent was removed under reduced pressure to give tert-butyl 7-(4-hydroxy-2-oxopyridin-1(2H)-yl)-5-methyl-3,4-dihydro-1H-pyrido[4,3-b]indole-2(5H)-carboxylate, which was used directly in the next step. To a solution of tert-butyl 7-(4-hydroxy-2-oxopyridin-1(2H)-yl)-5-methyl-3,4-dihydro-1H-pyrido[4,3-b]indole-2(5H)-carboxylate (800 mg, 2.02 mmol) in THF (10 mL) was added LiN(SiMe3)2 (1.0 M in THF, 2.6 mL, 2.6 mmol) followed by PhN(Tf)2 (0.94 g, 2.6 mmol) under an atmosphere of argon. The reaction was stirred at room temperature until complete. The solvent was removed under reduced pressure, and the residue was purified by flash column chromatography (silica gel, hexanes/EtOAc, 1:1) to give the title compound (0.42 g, 40% yield) as a white solid: 1H NMR (300 MHz, CDCl3) δ 7.57-7.53 (m, 2H), 7.30 (d, J=1.5 Hz, 1H), 7.02-6.99 (m, 1H), 6.60 (d, J=2.7 Hz, 1H), 6.27 (dd, J=7.8, 2.7 Hz, 1H), 4.65 (s, 2H), 3.85 (m, 2H), 3.65 (s, 3H), 2.84 (m, 2H), 1.51 (s, 9H); ESI MS m/z 528 [M+H]+.

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