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Reagents and conditions: (a) oxalic acid, 4 N HCl, reflux, 6 h; (b) POCl3, DMF, 50 °C, 6 h; (c) triethyl phosphite, sealed tube, 150 °C, 18 h; and (d) bromotrimethylsilane, dry DCM, stirring, room temperature, 18 h.
