Reaction Steps
A solution of 2-phenylthioethanol (3 g, 19 mmol) in benzene (5 mL) was added dropwise, at room temperature, to a solution of phosgene (1 mL, 1.9 M toluene, 1.9 mmol). After stirring for 3 h the excess phosgene and solvents were removed under vacuum to give 2-phenylthioethyl-chloroformate as a yellow oil which was used without further purification. A solution of alcohol 24 (27 mg, 45 μmol) and DMAP (38 mg, 0.31 mmol)in CH2Cl2 (5 mL) was treated, at 0° C., with 2-phenylthioethyl-chloroformate (38 mg, 0.18 mmol) and the mixture was stirred for 4 h. The reaction mixture was poured into brine (10 mL), extracted with CH2Cl2 (3×5 mL), dried (Na2SO4), concentrated, and purified by preparative TLC (20% EtOAc in benzene) to give carbonate 26 (30.7 mg, 88%):pale yellow oil; Rf =0.69 (20% EtOAc in benzene); [α]25D -150 (c0.20, CH2Cl2); IR (neat) νmax 2954, 2876, 1738, 1721, 1492, 1458, 1257, 1164 cm-1 ; 1H NMR (500 MHz, CDCl3) 7.41-7.40 (m, 2 H, Ph), 7.40-7.27 (m, 2 H, Ph), 7.26-7.19 (m, 1 H, Ph), 6.10 (rid, J=3.27, 9.02 Hz, 1 H, C=CHCH2), 5.87 (d, J=9.71 Hz, 1 H, CH=CHC≡CCH), 5.77 (b d, J=9.71 Hz, 1 H, CH=CHC≡CCH), 5.77 (b s, 1 H, CHOSi), 4.88 (dd, J=3.33, 13.52 Hz, 1 H, CHHOCO), 4.79 (dd, J=9.04, 13.54 Hz, 1 H, CHHOCO), 4.28-4.23 (m, 2 H, OCOCH2CH2SPh), 4.10-4.07 (m, 1 H, ehtylene ketal), 3.99-3.91 (m, 2 H, ethylene ketal), 3.88-3.84 (m, 1 H, ethylene ketal), 3.18 (dd, J=7.23, 7.40 Hz, 2 H, OCOCH2CH2SPh), 2.48 (d, J=13.24 Hz, 1 H, CHH-eq), 2.11 (d, J=13.25 Hz, 1 H, CHH-ax), 1.00-0.96 (m, 18 H, 2 x (Si(CH2CH3)3)), 0.79-0.67 (m, 12 H, 2 x (Si(CH2CH3)3)); 13C NMR (125 MHz, CDCl3) δ154.70, 138.17, 129.81, 129.07, 126.58, 124.11, 122.91, 122.46, 105.72, 68.04, 65.75, 65.52, 65.22, 63.71, 52.34, 31.95, 29.70, 7.07, 6.72, 6.16, 4.53; FAB HRMS (NBA/Csl) m/e 914.2180, (M+Cs+) calcd for C40H55NO9SSi:914.2190.
