Reaction Steps
TFA (9.20 mmol, 0.709 ml) was slowly added to a stirred solution of tert-butyl 4-hydroxy-9-methyl-2-oxo-1,2,5,6,8,9-hexahydro-7H-pyrido[2,3-d]azepine-7-carboxylate (0.541 g, 1.84 mmol) in DCM (20 ml) at room temperature. The reaction solution was stirred until all starting materials are consumed. The solvent was removed under reduced pressure and the resulting residue was dissolved in DCM (20 ml). Addition of Et3N (18.4 mmol, 2.56 ml) and TFAA (3.86 mmol, 0.511 ml) was followed by stirring for 8 h at room temperature. The reaction mixture was parted between sat. aq. NaHCO3 and DCM. The organic layer was dried over Na2SO4, concentrated under reduced pressure and purified to provide 277 mg (52%, two steps) of 4-hydroxy-9-methyl-7-(trifluoroacetyl)-1,5,6,7,8,9-hexahydro-2H-pyrido[2,3-d]azepin-2-one. MS (ESI) m/z 291 [M+1]+. POBr3 (0.533 mol, 153 mg) was added to a stirred solution of 4-hydroxy-9-methyl-7-(trifluoroacetyl)-1,5,6,7,8,9-hexahydro-2H-pyrido[2,3-d]azepin-2-one (77 mg, 266 μmol) in DMF (1 ml). The mixture was heated at 90° C. for 2 h, quenched with sat. aq. NaHCO3 and extracted with EtOAc. The organic layer was dried over Na2SO4, concentrated under reduced pressure and purified by column chromatography to furnish 47 mg (50%) of 4-bromo-9-methyl-7-(trifluoroacetyl)-1,5,6,7,8,9-hexahydro-2H-pyrido[2,3-d]azepin-2-one. MS (ESI) m/z 353/355. A mixture of 4-bromo-9-methyl-7-(trifluoroacetyl)-1,5,6,7,8,9-hexahydro-2H-pyrido[2,3-d]azepin-2-one (47 mg, 134 μmol), EtOH (2 ml) and 10% Pd/C was stirred for 5 minutes under H2 atmosphere (1 atm). The reaction was filtered through Celite and 35 mg (99%) of 9-methyl-7-(trifluoroacetyl)-1,5,6,7,8,9-hexahydro-2H-pyrido[2,3-d]azepin-2-one was obtained. MS (ESI) m/z 275. POBr3 (256 μmol, 73.5 mg) was added to a stirred solution of 9-methyl-7-(trifluoroacetyl)-1,5,6,7,8,9-hexahydro-2H-pyrido[2,3-d]azepin-2-one (35 mg, 128 μmol) in DMF (1 ml). The mixture was heated at 90° C. for 5 h, quenched with sat. aq. NaHCO3 and extracted with EtOAc. The organic layer was dried over Na2SO4, concentrated under reduced pressure and purified by column chromatography to furnish 24 mg (56%) of 2-bromo-9-methyl-7-(trifluoroacetyl)-6,7,8,9-tetrahydro-5H-pyrido[2,3-d]azepine. MS (ESI) m/z 337/339. Deprotection was carried out at 60° C. for 10 minutes using MeOH (1 ml), H2O (200 μl) and K2CO3 (30 mg) to render 15 mg (87%) of 2-bromo-9-methyl-6,7,8,9-tetrahydro-5H-pyrido[2,3-d]azepine. 1H-NMR (DMSO-d6) δ 7.42 (d, 1H), 7.35 (d, 1H), 4.25 (m, 2H), 3.86 (m, 2H), 3.18 (m, 2H), 2.84 (dd, 1H), 1.21 (d, 3H) ppm.
