N-methyl-2-pyrrolidone → (R)-tert-butyl 4-(4-chloropyrido[4,3-d]pyridazin-1-yl)-3-methylpiperazine-1-carboxylate

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To (R)-tert-butyl 3-methylpiperazine-1-carboxylate (3.30 g, 16.5 mmol) and 1,4-dichloropyrido[4,3-d]pyridazine 3 (3.00 g, 15.0 mmol), suspended in Hünig's base (9.14 ml, 52.5 mmol) was added NMP (6 ml). The reaction was stirred at 100° C. The reaction contents were poured into water (120 mL) and extracted with dichloromethane (3×50 mL). Silica gel chromatography (gradient elution 20 to 80% EtOAc in hexanes) afforded 110 mg of (R)-tert-butyl 4-(4-chloropyrido[4,3-d]pyridazin-1-yl)-3-methylpiperazine-1-carboxylate 26 eluting after the 1-substitution product. 1H NMR (500 MHz, CDCl3) δ ppm 9.66 (s, 1H) 9.06 (d, J=6.1 Hz, 1H) 7.77 (d, J=5.5 Hz, 1H) 3.28-4.23 (m, 7H) 1.51 (s, 9H) 1.28 (d, J=6.7 Hz, 3H).

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