Reaction Steps
Bistrimethylsilylacetamide (0.25 ml, 1 mmole) was added to a solution of 2-acetonyl-3,4-dihydroxy-5-(2,3-epoxy-5-hydroxy-4-methylhexyl)-2,3,5,6-tetrahydropyran (0.1 g, 0.33 mmole) in tetrahydrofuran (1 ml) at 0° C. and then stirred at room temperature for 0.5 hour. The solvent was then completely removed in vacuo at room temperature and the residue dissolved in tetrahydrofuran (1 ml) for use in the next stage. Triethyl phosphonoacetate (0.075 g, 0.33 mmole) in tetrahydrofuran (2 ml) was added dropwise to a stirred suspension of sodium hydride (0.01 g, 80% dispersion in oil) in tetrahydroduran (2 ml) at 0° under nitrogen over 15 min. The reaction mixture was then stirred under nitrogen at room temperature for 1 hour. The solution of silylated 2-acetonyl-3,4-dihydroxy-5-(5-hydroxy-2,3-epoxy-4-methylhexyl)-2,3,5,6-tetrahydropyran was then added dropwise over 15 min. to the reaction mixture kept at 0°. This was then kept at 60° for 15 min. The reaction mixture was poured into ice-water (3 g) and acidified to pH 2, keeping the solution homogeneous by the addition of ethanol. After 2 min aqueous sodium bicarbonate (10 ml) was added and the mixture was saturated with sodium chloride and extracted continuously with ether. The ethereal extract was dried and evaporated to give a mixture showing some starting material and two major products on tlc. Preparative tlc (developed three times by chloroform-methanol (93:7) separated these products into two bands, A (Rf = 0.45) and B (Rf = 0.40). Extraction of Band A with ethyl acetate (100 ml) afforded ethyl 4-[3,4-dihydroxy-5-(2,3-epoxy-5-hydroxy-4-methylhexyl)-2,3,5,6-tetrahydropyran-2-yl]-3-methylbut-2Z-enoate (0.021 g), λmax 221 (εm 9,700)nm; νmax (CHCl3) 1690, 1640, 1262, 1155, 1085, and 1060 cm-1 ; δ H (CDCl3) 5.93 (1H, m, --CH=), 4.25 (2H, q, J=7 Hz, --CO2CH2CH3), 2.06 (3H, s, ##STR12## 1.30 (3H, t, J=7 Hz, --CO2CH2CH3), 1.25 (3H, d, J=7 Hz, CH3CH), and 0.96 (3H, d, J=7 Hz, CH3CH); m/e (relative intensity) 372 (M+, 0.5), 354 (1), 336(2), 327(2), 309(4), 291(9), 227(100), 224(69), and 209(23) (Found: C, 61.85; H, 9.20%. C19H32O7 requires C, 61.25; H, 8.65%). Extraction of Band B with ethyl acetate gave ethyl 4-[3,4-dihydroxy-5-(2,3-epoxy-5-hydroxy-4-methylhexyl)-2,3,5,6-tetrahydropyran-2-yl]-3-methylbut-2E-enoate (0.069 g), [α]D - 1.44° (c, 1.8 CHCl3); λmax 220 (εm 11,100) nm: εmax (CHCl3) 1705, 1650, 1155, and 1050 cm-1 ; δH (CDCl3) 5.86 (1H, m, --CH=), 4.23 (2H, q, J=7 Hz, --CO2CH2CH3), 2.70-2.90 (2H, m, ##STR13## 2.26 (3H, s, ##STR14## 1.30 (3H, t, J=7 Hz, --CO2CH2CH3), 1.25 (3H, d, J=7 Hz, CH3CH), and 0.95 (3H, d, J=7 Hz, CH3CH); m/e (relative intensity) 372 (M+, 2), 354(2), 354(2), 336(3), 327(6), 309(7), 291(6), 270(11), 264(13), 245(10), 244(10), 227(100), 224(30), and 209(35) (Found: M+ 372.2150 C19H32O7 requires M+ 372.2148).
