General procedure for the synthesis of 6-chloropyrido[3,2-b]pyrazines from 6-chloro-2,3-diaminopyridine and glyoxal (Intermediate 4.2): 6-chloro-2,3-diaminopyridine (1 g, 6.96 mmol, 1 eq.) was dissolved in THF (15 mL) at room temperature, followed by addition of glyoxal (0.84 mL, 18.1 mmol, 2.5 equivalent). The reaction mixture was stirred at room temperature for 2 h. The reaction progress was monitored by RP-HPLC. Upon completion of the reaction, THF was removed by evaporation and the residue was redissolved in ethyl acetate (30 mL). The organic phase was washed twice with saturated Na2CO3 solution, dried over magnesium sulfate and the solvent was evaporated in vacuum to afford 1.15 g of the target compound 6-chloropyrido[3,2-b]pyrazine (Intermediate 4.2) as a white solid. Yield: 1.15 g; Yield: 100%; Molecular formula: C7H4N3Cl; HPLC purity: 98%; HPLC conditions (H2O containing 0.1% TFA-ACN containing 0.05% TFA): retention time: 1.2 min; % area: 98%; 1H NMR (CDCl3) δ: 9.0 (s, 1H), 8.88 (s, 1H). 8.36 (d, 1H, J=8Hz), 7.67 (d, 1H, J=8Hz); LC-MS: m/z ESI: retention time 0.68 min, 167.0 (M+1).
![6-chloropyrido[3,2-b]pyrazine](/CAS/GIF/68236-03-3.gif)