2,3-Diaminopyridine → 2-Methylpyrido[2,3-b]pyrazin-3(4H)-one

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Reaction Steps

Ethyl pyruvate (1.22 mL) was dissolved in methanol (10 mL) and added to a cold solution of 2,3-diaminopyridine (1.09 g) in methanol MeOH (20 mL) and the mixture was stirred at ambient temperature. The solid was filtered off and washed with cold methanol to afford 2-methyl-4H-pyrido[2,3-b]pyrazin-3-one (1.1 g) as a grey solid. 1.0 g of this material was suspended in acetonitrile (10 mL) and phosphoryl chloride (1.16 mL) was added. The mixture was heated at 120° C. for 0.5 h under MW conditions. The crude mixture was partitioned between water and EtOAc. The organic layer was washed with brine, dried over Na2SO4, filtered, and concentrated in vacuo to afford IIId (460 mg) as a red solid sufficiently pure for the next step.

Provenance & Evidence