2488
H. RAVINDRANATH AND G. V. M. SHARMA
Zinc-mediated Barbier allylation of 13 gave allylic alcohols 14 as an insepar-
able mixture (80%), which on oxidation with Dess–Martin periodinane in anhydrous
CH2Cl2 gave the ketone 2 in 75% yield. Attempted removal of the PMB group in 2
oxidatively with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ)[10] in aqueous
CH2Cl2 gave an unexpected a=b-unsaturated ketone 15 in 63% yield. Further
attempts to deprotect the PMB group in 2 with other reagents such as TMSCl,
anisole, SnCl2 (cat.)[11] in CH2Cl2, and ceric ammonium nitrate (CAN)[12] in
CH2Cl2=H2O) did not give the desired product 2a. Several attempts for the conver-
sion of 2 to form the expected ketol 2a met with failure.
EXPERIMENTAL
1-((4R,5R)-5-((R)-3-(Benzyloxy)-1-(4-methoxybenzyloxy)propyl)-2,2-
dimethyl-1,3-dioxolan-4-yl)pent-4-en-2-one (2)
To a stirred solution of diastereomeric mixture of alcohol 14 (2.1 g, 4.4 mmol)
in anhydrous CH2Cl2 (1.5 mL) under N2 atmosphere at 0 °C, Dess–Martin periodi-
nane (2.2 g, 5.3 mmol) and NaHCO3 (0.56 g, 6.7 mmol) were added and stirred at
room temperature for 2 h. Workup as described for 13 and purification of the residue
by column chromatography (silica gel, 60–120 mesh, EtOAc=hexane, 1:9) furnished 2
25
(1.5 g, 75%) colorless thick syrup. ½aꢁD ¼ 70:03 (c 0.3, CHCl3); IR (CHCl3): 3068,
2923, 1720, 1661, 1513, 1455, 1377, 1302, 1242, 1213, 1093, 915, 878, 849, 820,
1
735, 699, 667 cmꢀ1; H NMR (300 MHz, CDCl3, 295 K): d 7.21 (m, 7H, Ar-H),
6.81 (d, 2H, J ¼ 8.5 Hz, Ar-H), 5.75 (m, 1H, olefinic), 5.0–5.1 (m, 2H, olefinic),
4.35–4.48 (m, 4H, 2 × ArCH2), 4.0 (m, 1H, OCH), 3.15–3.81 (m, 4H, OMe, OCH),
3.05–3.18 (m, 3H, 3 × OCH), 2.91 (m, 2H, CH2), 1.75–1.98 (m, 2H, 2 × CH), 1.55–
1.74 (m, 2H, 2 × CH), 1.35 (s, 3H, CH3), 1.40 (s, 3H, CH3); 13C NMR (75 MHz,
CDCl3): d 206.8, 159.1, 138.3, 134.3, 130.6, 129.5 (2C),128.3 (2C), 127.6 (3C),
118.1, 113.7 (2C), 108.3, 83.09, 75.6, 74.0, 73.0, 71.5, 66.7, 55.2, 39.8, 37.8, 35.0,
27.3 (2C). HRMS (ESI): m=z calculated for C28H37O6[MþH]þ: 470.1256; found:
470.1254.
(E)-1-((4R,5R)-5-((R)-3-(Benzyloxy)-1-hydroxypropyl)-2,2-dimethyl-
1,3-dioxolan-4-yl)pent-3-en-2-one (15)
To a solution of 2 (1.5 g, 3.2 mmol) in CH2Cl2=H2O (10 mL; 19:1), DDQ (0.8 g,
3.8 mmol) was added and stirred at room temperature 1 h. The reation mixture was
quenched with saturated NaHCO3 solution (10 mL), filtered, and washed with
CH2Cl2(20 mL). The filtrate was washed with water (15 mL), brine (10 mL), and
dried (Na2SO4). Solvent was evaporated under reduced pressure and the residue
was purified by column chromatography (silica gel, 60–120 mesh, EtOAc:n–hexane,
25
1:9) to furnish 15 (0.7 g, 63%) colorless liquid. ½aꢁD ¼ 58:6 (c 0.4, CHCl3); IR
(CHCl3): 3018, 2935, 2872, 1714, 1623, 1513, 1452, 1379, 1315, 1275, 1214, 1164,
1
1091, 1027, 972, 927, 840, 840, 744, 666, 626 cmꢀ1; H NMR (300 MHz, CDCl3): d
7.32 (m, 5H, Ar-H), 7.08 (m, 1H, olefinic), 6.65 (m, 1H, olefinic), 4.51
(s, 2H, PhCH2), 4.29 (m, 1H, OCH), 4.18 (m, 1H, OCH), 4.04 (m, 2H, 2 × OCH),
3.74–3.62 (m, 3H, OCH, COCH2), 3.30 (brs, 1H, OH), 1.96–1.87 (m, 2H, CH2),