Reaction Steps
The synthesis of this compound follows the same general route outlined in scheme 5 [see Preparative Example 2.01]. To a suspension of ethyltriphenylphosphonium bromide (2.9 g, 6.93 mmol) in dry THF (15 mL) under argon at 0° C. was added 1.6 M BuLi in THF (4 mL, 6.40 mmol) and the deep red solution left stirring without cooling for 10 min. After re-cooling to 0° C., the aldehyde 46 (580 mg, 2.69 mmol) in THF (10 mL) was added and the mixture stirred at r.t. for 12 h. The reaction was then quenched with water (1 mL) and extracted with dichloromethane (100 mL). The organic phase was washed with sat. aq. NaHCO3 (15 mL) then water (15 mL), dried over MgSO4) and concentrated in vacuo. The residue was subjected to chromatography to afforded (3R,4S)-N-tert-butoxycarbonyl-3-hydroxy-4-propenyl-pyrrolidine (50) as a light yellow syrup (165 mg, 27%). To a solution of intermediate 50 (165 mg, 0.73 mmol) in ethanol (10 mL) was added 10% Pd/C (60 mg) and the suspension was stirred under an atmosphere of hydrogen for 3 h. After filtration, the solvent was removed in vacuo to give (3R,4S)-N-tert-butoxycarbonyl-3-hydroxy-4-propyl-pyrrolidine (51) as a syrup (172 mg, 102%). 1H NMR (300 MHz, CDCl3): δ ppm: 3.98-3.96 (m, 1H), 3.61-3.57 (m, 3H), 3.22-3.18 (m, 1H), 3.10-3.01 (m, 1H), 2.03 (m, 1H), 1.45 (s, 9H), 1.41-1.31 (m, 2H), 1.24-1.12 (m, 1H), 0.94-0.89 (m, 3H). 13C NMR (300 MHz, CDCl3): δ ppm (note that some peaks are doubled due to slow conversion of rotamers): 155.20, 79.69, (75.53, 74.76), (53.10, 52.80), (49.94, 49.38), (46.19, 45.67), 34.04, 28.83, 21.27, 14.47. To a solution of intermediate 51 (172 mg, 0.75 mmol) in methanol (10 mL) was added 12N (conc.) HCl (4 mL) and the solution stirred at 40° C. for 30 min. After removal of the solvent in vacuo and azeotroping with toluene, the crude title compound (3R,4S)-3-hydroxy-4-propyl-pyrrolidine hydrochloride (52) was obtained as a syrup (138 mg, 0.83 mmol, 111%). 1H NMR (300 MHz, MeOH-d4): δ ppm: 4.20-4.16 (m, 1H), 3.59-3.52 (m, 1H), 3.44-3.39 (m, 1H), 3.19-3.14 (m, 1H), 3.05-2.99 (m, 1H), 2.23-2.17 (m, 1H), 1.55-1.28 (m, 4H), 0.98-0.94 (m, 3H). 13C NMR (300 MHz, MeOH-d4): δ ppm: 75.65, 52.82, 50.30, 47.45, 34.69, 22.30, 14.78.
