[NH:1]1[CH2:5][CH2:4][CH2:3][CH2:2]1.C[C:7]#[C:8][C:9]([O-])=[O:10].Cl>O.CO.C(Cl)Cl>[C:9]([N:1]1[CH2:5][CH2:4][CH2:3][CH2:2]1)(=[O:10])[C:8]#[CH:7]To a stirred solution of pyrrolidine (4.2 mL, 50.0 mmol) in water (25 mL) and MeOH (35 mL) at −50° C. was added methylpropiolate (4.5 mL, 50.0 mmol) dropwise. The reaction mixture was stirred at this temperature for 5 h then diluted with DCM (200 mL). 2M aqueous HCl (200 mL) was added and the layers were separated. The aqueous layer was extracted with DCM (2×100 mL). The combined organic layers were washed with aqueous sat. NaHCO3 (200 mL), water (200 mL), then brine (200 mL), dried (Na2SO4), filtered and concentrated in vacuo to give the title compound (6.0 g, 98%) as a white solid that was used without further purification. δH (CDCl3) 3.68 (2H, t, J 6.8 Hz), 3.50 (2H, t, J 6.3 Hz), 3.04 (1H, s), 2.01-1.90 (4H, m).
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