C([O:7][CH2:8][CH3:9])(=O)CCC=C.C[N+]1([O-])CC[O:14][CH2:13]C1.C[OH:19].ClCCl.[O:23]1[CH2:27][CH2:26][CH2:25][CH2:24]1>O.[Os](=O)(=O)(=O)=O>[CH2:8]([O:7][C:27](=[O:23])[CH2:26][CH2:25][CH:24]([OH:19])[CH2:13][OH:14])[CH3:9]
A solution of ethyl pent-4-enoate (11.7 g, 91.3 mmol) in tetrahydrofuran (420 mL) and water (40 mL) is treated with osmium tetroxide (1.0 g, 4.2 mmol) and 4-methylmorpholine N-oxide (32.5 mL, 50% in water) at room temperature and stired for 3 h, at which time no more starting material is detectable by TLC (SiO2, 2% methanol/dichloromethane, Rf=0.40). The mixture is concentrated in vacuo and the residue chromatographed on SiO2 (2% methanol/ethyl acetate) to afford the title compound 14.37 g (96%) as a colorless oil.
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