Synthesis
General procedure for the synthesis of tert-butyl 2-chloropyridine-4-carbamate from 2-chloro-4-aminopyridine and di-tert-butyl dicarbonate: In the presence of 95 mg of 4-dimethylaminopyridine (DMAP), 1.69 g (7.78 mmol, 1 eq.) of di-tert-butyl dicarbonate was dissolved in 50 mL of dichloromethane, and slowly added to a 30 mL solution of dichloromethane containing 1 g (7.78 mmol, 1 eq.) of 2-chloro-4-aminopyridine and 1.19 mL (1.19 mmol, 1.1 eq.) of triethylamine in 30 mL of dichloromethane. The reaction mixture was stirred overnight at room temperature. Upon completion of the reaction, the reaction was quenched by the addition of 100 mL of water and subsequently extracted with dichloromethane. The organic phases were combined and dried over anhydrous sodium sulfate. After evaporation of the solvent under reduced pressure, the residue was purified by silica gel column chromatography (eluent ratio varied from 70/30 to 50/50 heptane/ethyl acetate gradient). The resulting oil was crystallized from pentane to give 1.40 g tert-butyl 2-chloropyridine-4-carbamate in 80% yield.
References
[1] Patent: WO2006/53791, 2006, A2. Location in patent: Page/Page column 49-50
[2] Tetrahedron Letters, 2014, vol. 55, # 49, p. 6734 - 6737
[3] Patent: WO2005/33072, 2005, A2. Location in patent: Page/Page column 26
[4] Patent: WO2004/43926, 2004, A1. Location in patent: Page 161
[5] Patent: US2004/102450, 2004, A1. Location in patent: Page/Page column 100
