Phosphorus oxychloride → Methyl 4-chloroquinoline-6-carboxylate

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Reaction Steps

To 6-(methoxycarbonyl)quinoline-N-oxide from the above step was added phosphoryl trichloride (5 mL, 54.6 mmol). The resulting mixture was then stirred at rt under N2 for 2 h. The reaction was then slowly quenched by addition to an ice cold solution of saturated aqueous NaHCO3 (50 mL) in an ice bath with rapid stirring. The aqueous solution was extracted with EtOAc (3×50 mL). The organic layers were combined, washed with saturated aqueous NaHCO3 (25 mL), H2O (25 mL), dried (MgSO4), and concentrated. Purification by ISCO (40 g SiO2, 0-50% EtOAc/hexanes) gave as the major product, methyl 4-chloroquinoline-6-carboxylate (330 mg, 1.489 mmol, 25.8% yield over 3 steps) (m/z=221.9) as a white solid. Also isolated was the more polar, methyl 2-chloroquinoline-6-carboxylate with same mass (m/z=221.9).

Provenance & Evidence