To a mixture of (R)-1-(tert-butoxycarbonyl)pyrrolidine-2-carboxylic acid (5.8 g, 27 mmol) and potassium carbonate (8.6 g, 62 mmol) in tetrahydrofuran (160 mL) was added iodomethane (4.0 mL, 65 mmol). The reaction mixture was heated to reflux for 17 hours and subsequently cooled to room temperature. The reaction mixture was filtered and the filtrate was concentrated under reduced pressure. The crude product was purified by automated column chromatography using petroleum ether/ethyl acetate (3:1, v/v) as eluent to afford (R)-1-tert-butyl 2-methyl pyrrolidine-1,2-dicarboxylate (6.0 g, 65% yield) as a yellow oil.
