Phosphoric Acid → 4-(2-Chloro-pyrido[2,3-d]pyrimidin-4-yl)-piperazine-1-carboxylic acid tert-butyl ester

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Reaction Steps

A mixture of 2,4-dichloro-pyrido[2,3-d]pyrimidine (150 mg, 0.75 mmol, 1 eq) [prepared from 2-aminonicotinic acid by the methods of Robins et al. (J. Am. Chem. Soc. 1955, 77, 1045.) and Oakes et al. (J. Chem. Soc. 1956, 1045.)], N-t-butoxycarbonyl piperazine (147 mg, 0.787 mmol, 1.05 eq) and Hunig's base (0.39 mL, 2.25 mmol, 3 eq) in ethanol (2.5 mL) was stirred at rt for 17 hr. The white solid was collected by filtration, washed with water and cold ethanol, and dried to afford C1.1 (105 mg, 40% yield). LC/MS: 350.41 [M+H]+; HPLC: >95% at 1.44 min (Xterra 5 μm C18 column 4.6×30 mm, 10-90% aqueous methanol over 2 min containing 0.2% phosphoric acid, 5 mL/min, monitoring at 254 nm).

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