Phosphorus trichloride → TRANS 5-(t-BUTYLDIPHENYLSILYLOXYMETHYL)-2-(DIETHYLOXYPHOSPHINOYL)-1,3-OXATHIOLANE

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Reaction Steps

A solution of triethylorthoformate (0.64 g, 4.33 mmol), 1-t-butyldiphenylsilyloxy-3-mercapto-2-propanol (example 24) (5.00 g, 46.23 mmol) and p-toluenesulfonic acid (20 mg) in toluene (60 mL) was heated to reflux for 2h. The solvent was removed under reduced pressure to give a yellow oil. The oil was dissolved in dichloromethane (20.mL), zinc chloride (20 mg) was added along with triethyl phosphite (0.32 g, 1.93 mmol) at 0° C., followed by the addition of phosphorous trichloride (0.13 g, 0.95 mmol). After stirring at room temperature for 18h the solvent was removed under reduced pressure to give a colourless oil. The crude material was purified by flash chromatography with a mixture of hexanes and ethyl acetate (50:50) to give the compound as a colourless oil (0.97 g) in 67% yield as a mixture of cis and trans isomers (1:3.5). 1H NMR (300MHz, CDCl3) d: 1.03 (s, 9H, t-butyl), 1.32 (t, 6H, J=7.0Hz, CH3), 3.02 (m, 1H, H-4a), 3.18 and 3.24 (2dd, 1H, J=10.0 Hz, 6.0 Hz, H-4b), 3.72 (m, 2H, CH2OSi), 4.20 (m, 4H, CH2 CH3), 4.64 (p, 1H, J=6 Hz, H-5), 5.25 and 5.27 (2d, 1H, 2 JHP =9 Hz, H-2), 7.38 and 7.63 (m, 10H, Ar-H).

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