Step 2: Synthesis of tert-butyl (2-formylpyridin-3-yl)carbamate (10b)
To a solution of compound 10a (2.9 g, 10.7 mmol) in tetrahydrofuran (THF, 30 mL) was slowly added n-butyllithium (n-BuLi, 2.5 M, 8.5 mL, 21.4 mmol) at -78 °C and protected by nitrogen (N2). The reaction mixture was stirred continuously at this temperature for 1 hour. Subsequently, N-formylpiperidine (1.3 mL, 11.8 mmol) was added under fast stirring conditions. The reaction system was warmed up to 0 °C and stirring was continued for 1 hour. Upon completion of the reaction, it was partitioned with 1.5 M hydrochloric acid (HCl) solution. The pH of the aqueous layer was adjusted to 7 by addition of solid sodium carbonate (Na2CO3).The aqueous layer was extracted twice with ethyl acetate (EA), the organic layers were combined and dried with anhydrous sodium sulfate (Na2SO4). After concentration under reduced pressure, purification by column chromatography (CC, petroleum ether/ethyl acetate = 3/1) afforded the target compound 10b (1.5 g, 65% yield) as a white solid.
