Reaction Steps
A solution of allyl chloroformate (29.2 mL, 33.2 g, 275 mmol) in THF (30 mL) was added dropwise to a suspension of trans-4-hydroxy-L-proline (11) (30 g, 229 mmol) in a mixture of THF (150 mL) and H2O (150 mL) at 0° C. (ice/acetone), whilst maintaining the pH at 9 with 4 N NaOH. After stirring at 0° C. for 1 hour at pH 9, the aqueous layer was saturated with NaCl, and the mixture diluted with EtOAc (100 mL). The aqueous layer was separated, washed with EtOAc (100 mL) and the pH adjusted to 2 with conc. HCl. The resulting milky emulsion was extracted with EtOAc (2×100 mL), washed with brine (200 mL), dried (MgSO4), filtered and evaporated in vacuo to give the allyl carbamate 12 as a clear viscous oil (42.6 g, 87%): [α]20D=−62.1° (c=0.69, MeOH); 1H NMR (270 MHz, CDCl3+DMSO-d6)(Rotamers) δ 5.98-5.81 (m, 1H, NCO2CH2CH═CH2), 5.40-5.14 (m, 2H, NCO2CH2CH═CH2), 4.64-4.42 (m, 4H, NCO2CH2CH═CH2, NCH2CHOHCH2 and CHCO2H), 3.82-3.51 (m, 2H, NCH2CHOHCH2), 2.34-2.08 (m, 2H, NCH2CHOHCH2); 13C NMR (67.8 MHz, CDCl3+DMSO) (Rotamers) δ 175.0 and 174.5 (CO2H), 155.1 and 154.6 (NC═O), 132.9 and 132.8 (NCH2CH2CH═CH2), 117.6 and 116.7 (NCO2CH2CH═CH2), 69.5 and 68.8 (NCH2CHOH), 65.9 and 65.8 (NCO2CH2CH═CH2), 58.0 and 57.7 (CHCO2H), 55.0 and 54.5 (NCH2CHOH), 39.3 and 38.3 (NCH2CHOHCH2); MS (EI), m/z (relative intensity) 215 (M+., 10) 197 (12), 170 (M-CO2H, 100), 152 (24), 130 (M-CO2C3H5, 97), 126 (34), 112 (50), 108 (58), 86 (11), 68 (86), 56 (19); IR (Neat) 3500-2100 (br, OH), 2950, 1745 and 1687 (br, C═O), 1435, 1415, 1346, 1262, 1207, 1174, 1133, 1082, 993, 771 cm−1; exact mass calcd for C9H13NO5 m/e 215.0794, obsd m/e 215.0791.
