[CH3:1][O:2][CH:3]([O:16][CH3:17])[C:4]1[N:13]=[C:12]2[C:7]([CH2:8][CH2:9][CH2:10][NH:11]2)=[CH:6][C:5]=1[O:14][CH3:15].[C:18]1([O:24][C:25](=O)[O:26]C2C=CC=CC=2)[CH:23]=[CH:22][CH:21]=[CH:20][CH:19]=1.[Li+].C[Si]([N-][Si](C)(C)C)(C)C>C1COCC1>[CH3:17][O:16][CH:3]([O:2][CH3:1])[C:4]1[N:13]=[C:12]2[C:7]([CH2:8][CH2:9][CH2:10][N:11]2[C:25]([O:24][C:18]2[CH:23]=[CH:22][CH:21]=[CH:20][CH:19]=2)=[O:26])=[CH:6][C:5]=1[O:14][CH3:15]A solution of 7-(dimethoxymethyl)-6-methoxy-1,2,3,4-tetrahydro-1,8-naphthyridine (intermediate 309, 76 mg, 0.319 mmol) and diphenylcarbonate (137 mg, 0.638 mmol) in THF (2 ml) at −15° C. was treated drop wise with LHMDS (1 M in THF, 0.35 ml, 0.35 mmol) and stirred for 25 min. The reaction mixture was then quenched with sat. aq. NH4Cl and extracted with EtOAc (2×). The combined organic layers were washed with brine, dried over Na2SO4, filtered and concentrated under reduced pressure. The crude material was purified by normal phase chromatography (12 g silica gel cartridge, heptanes/EtOAc 100:0 to 0:100) to give the title compound as a yellow oil. (UPLC-MS 1) tR 0.93 min; ESI-MS 360.1 [M+H]+.
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