将醇转换为硫代碳酸酯再脱除羟基

有时候在底物有许多敏感官能团，上述方法无法得到较好的结果时，我们就需要将醇羟基转化为相应的硫代碳酸酯，再用自由基还原去除。

PART 01

将醇用硫代氯甲酸苯酯转换为相应的硫代碳酸苯酯，再自由基脱除

Phenyl thiochloroformate (0.55mL,3.92 mmol) was added to a stirred solution of compound 1 (1.22 g,3.565 mmol) and pyridine (1.45ml, 17.8mmol) in dichloromethane (50mL) at room temperature. The mixture was stirred for 2 hours, and the solvent was then evaporated. Flash chromatography of the residue over silica gel (2x15 cm), using 1:4 ethyl acetate-hexane, gave compound 2 (1.57g, 97%).Tributylstannane (1.31mL, 4.88mmol) and 2,2'-azobis[2-methylpropionitrile] (50 mg). The mixture was refluxed for 2h.and then the solvent was evaporated. Flash chromatography of the residue over silica gel(3x15cm), using 1:4 ethyl acetate-hexane, gave 3(1.05g, 99%).

Reference:J.Heterocycl.Chem.1999,36(3),653-658

PART 02

将醇转换为相应的硫代碳酸甲巯基酯，再自由基脱除

Sodium hydride(50%suspension in oil,75mg,7.5 mmol)was added to a cold solution (0℃)of alcohol 1(1.5g,4.9 mmol)in dry THF(50 mL)and,30 min later,0.87mL(14.7mmol)of carbon disulfide. The resulting mixture was stirred for 1.5h at 0℃ before addition of methyl iodide(0.9 mL,14.7 mmol).The mixture was allowed to reach room temperatureand stirred overnight. The solvent was removed under reduced pressure, and the remaining residue was dissolved in toluene(30 mL)and filtered. To the filtrate containing 18 were added tribytyltin hydride(1.57mL,5.9mmol) and AIBN(20 mg).This mixture was refluxed under argon for 2.5 h,After cooling and filtration, the solution was evaporated under reduced pressure, and the residue was chromatographed on silica gel with hexane-EtOAc(9:1)aseluen to give 840mg(60%)of 19 as a crystalline compound

Reference:J.Org.Chem.1991,56(1),405-411

PART 03

将醇用硫代羰基二咪唑转换为相应的硫代碳酸咪唑，再自由基脱除

A mixture of the title compound of preparation 1(420 mg,1.0 mmol) and thiocarbonyldiimidazole (890 mg,5.0 mmol) in dichloromethane (10ml) was stirred at room temperature for 24 hours.The reaction mixture was poured into water (20 mL),the layers separated, and the aqueous phase extracted with dichloromethane(3x40mL).The combined organic extracts were dried over MgSO4 and evaporated under reduced pressure.The residue was purified by column chromatography on silica gel to afford the title compound as a yellow oil(469mg).

A solution of 2(180 mg,0.34 mmol)in toluene (10 mL)was added dropwise to a solution of tri-n-butyltin hydride(291 mg,1 mmol)in Toluene(10mL)under reflux,o ver 30 minutes, and the reaction heated for a further 3 hours under reflux.The cooled reaction mixture was purified directly by column chromatography on silica gel to afford the title compound as a yellow gum(32mg)