Dimethylacetamide → Diethyl 2-(4-(3,4-dibromophenylamino)pyrido[3,4-d]pyrimidin-6-ylamino)-2-oxoethylphosphonate

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To a stirred mixture of CDI (2.74 g, 16.9 mmol) and dry THF (13 mL), at room temperature and under a nitrogen atmosphere, was added a solution of 2-(diethoxyphosphoryl)acetic acid (2.96 g, 15.1 mmol) in THF (10 mL). After addition the reaction mixture was stirred further at 40° C. (bath) for 15 min (whence evolution of gases ceased). A solution of compound 225 (2.38 g, 6.02 mmol) in a mixed solvents of dry THF (7 mL) and DMA (8 mL) was added and stirred further at 40° C. The reaction was monitored by TLC (dichloromethane-MeOH=15:1). After stirred for 4 h, the reaction mixture was poured into water (250 mL) and stirred with petroleum ether (350 mL) at room temperature for 20 min. Petroleum ether layer was decanted. It was repeated once more with petroleum ether (200 mL). The solid was collected by suction filtration; washed with water (5×30 mL) and dried to give diethyl 2-(4-(3,4-dibromophenylamino)pyrido[3,4-d]pyrimidin-6-ylamino)-2-oxoethylphosphonate (234) (3.28 g, 95%); mp 120-124° C.; 1H NMR δ [(CD3)2SO]: 10.89 (s, 1H), 10.41 (s, 1H), 9.04 (s, 1H), 8.88 (s, 1H), 8.67 (s, 1 H), 8.34 (d, J=2.5 Hz, 1H), 7.87 (dd, J=8.8, 2.5 Hz, 1H), 7.77 (d, J=8.8 Hz, 1H), 4.17-4.03 (m, 4H), 3.32 (d, J=21.6 Hz, 2H), 1.26 (t, J=7.0 Hz, 6H). Anal. Calcd for C19H20Br2N5O4P: C, 39.81; H, 3.52; N, 12.22%. Found C, 39.48; H, 3.78; N, 11.79%.

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