Reaction Steps
To a solution 7a (100 mg, 0.28 mmol) in THF (8 mL) and toluene (8 mL), maintained at -78° C., was added diethyl azodicarboxylate (DEAD, 0.455 mL, 2.88 mmol), PMe3 (2.89 mL, 1.0M solution in THF), and chloroacetic acid24 (220 mg, 2.32 mmol). The reaction mixture was stirred at -78° C. and allowed to warm to -30° C. over a period of 1.5 h (until complete disappearance of starting material was observed by TLC). Ammonium hydroxide (5 mL) was then added, and the solution was concentrated under reduced pressure. The residue obtained was then treated with ammonium hydroxide (5 mL) in CH3CN (10 mL), and the mixture was stirred for 4 h. The mixture was then quickly extracted with ether, the organic layer was dried (MgSO4), concentrated, and submitted for silica gel chromatography (Solvent A) to give 81 mg (81%) of 8a as a colorless syrup: [α]D20 +106° (c 1.1, CHCl3); 1H NMR (CDCl3): δ0.99 (t, 3 H, J=7.3 Hz, --CH2CH2CH3), 1.12 (d, 3 H, J=6.8 Hz, --CHCH3), 1.38 and 1.40 [2d, 6 H, J=5.8 Hz, --CH(CH3)2 ], 1.42 [d, 3 H, J=6.5 Hz, --CH(CH3)], 1.60 (m, 2 H, J=7.48 Hz, --CH2CH2 CH3), 1.93 (m, 1 H, H-9), 2.87 (m, 2 H, --CH2CH2 CH3), 3.59 (bs, 1 H, --OH), 3.91 (m, 1 H, H-8), 4.62 [m, 1 H, J=6.0 Hz, --CH(CH3)2 ], 4.70 (d, 1 H, J=7.6 Hz, H-10), 5.92 (s, 1 H, H-3), 6.21 (s, 1 H, H-6); 13C NMR (CDCl3): δ 13.87, 15.73, 18.95, 21.66, 21.80, 23.19, 39.02, 40.48, 66.66, 70.77, 77.00, 96.92, 104.83, 106.14, 110.02, 155.69, 156.15, 157.75, 159.06, 160.48. Anal. Calcd for C20H26O5.0.03CH2Cl2 : C, 65.50; H, 7.21. Found: C, 65.74; H, 7.39.
