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1.31 g of thiol (19) were dissolved in a mixture of 31.1 mL of Ethyl Acetate and 6.21 mL of deionized H2O at 23 °C. This mixture was then treated with 1.66 g of NBS and stirred for 12 h. The resulting solution was diluted with 50 mL of Et2O and washed twice with 50 mL of saturated Na2SO3(aq) . Then it was washed twice with 50mL of saturated NaHCO3(aq), dried over MgSO4, and concentrated under reduced pressure to yield the crude lactol.
The crude lactol was purified by silica gel chromatography (Developing Solvent 3:7EtOAc/cyclohexane) to yield 1.01 g of the intermediate lactol in 91% yield. The 400 mg of the lactol was dissolved in 13.4mL of CH2Cl2 at 23 °C and was treated with 415 mg of F3CC(NPh)Cl and then 665 mg of Cs2CO3. The mixture was stirred vigorously for 1 h. The mixture was then diluted with cyclohexane, filtered over Celite, and concentrated. The crude oil was then purified by column chromatography (Developing Solvent 2:8EtOAc/hexanes) to yield (20)
Main Reagents:
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•NBS – N-Bromosuccinimide is a brominating and an oxidizing agent that acts as agreat source of cationic bromide. Because of this, it is often used in radical substitution and electrophilic addition reactions in organic chemistry. As a result of its chemical properties, reactions with NBS are often highly exothermic, so they need to be done in controlled environments.
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•Cs2CO3 – Cesium Carbonate is useful as a base in organic chemistry, as it is more soluble in organic solvents than most carbonates. It is often used to create other cesium salts in reactions with protic acids. Currently, cesium carbonate is being used to aid in cancer treatments. Because of its basicity, it increases the pH of cancer cells, which causes them to die.
Reference:
Pragani, R.; Seeberger, P. H. J. Am. Chem. Soc. 2010, 133, 102-107.
