Synthesis
General procedure for the synthesis of 3-bromo-5-(2-pyrrolidinyl)pyridine from 3-bromo-5-(3,4-dihydro-2H-pyrrol-5-yl)pyridine: 3-bromo-5-(3,4-dihydro-2H-pyrrol-5-yl)pyridine (2.0 g, 8.8 mmol) was dissolved in 80 mL of a mixed solvent of 80:20 (v/v) methanol/acetic acid, and the reaction was carried out using a dry ice-acetonitrile bath The reaction mixture was cooled to -40 °C. Sodium borohydride (747 mg, 19.75 mmol) was added to the reaction mixture in batches under vigorous stirring, and the addition process was controlled to be completed within 10 min. During the addition process, the reaction temperature was increased to -20 °C. After the reaction mixture warmed up to room temperature, most of the solvent was removed using a rotary evaporator. Water (200 mL) was added to the residue and the solution was adjusted to alkaline with sodium hydroxide. Subsequently, extraction was performed with dichloromethane (2 x 90 mL). The organic phases were combined, washed with saturated saline, dried over anhydrous potassium carbonate, filtered and concentrated. The crude product was purified by silica gel column chromatography (10×4 cm) with eluent of 1:1 (v/v) ethyl acetate-methanol to afford the target compound 3-bromo-5-(2-pyrrolidinyl)pyridine as a yellow oil in 1.8 g (90% yield). The product was structurally confirmed by NMR hydrogen (400 MHz, CDCl3) and carbon (100 MHz, CDCl3) spectra.
References
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