Chugaev Elimination

1. Preparation of xanthates from the corresponding alcohols (1°, 2°, 3°) by first deprotonating the alcohol with a base and reacting the resulting alkoxide with carbon disulfide. 2. The metal xanthate is then trapped with methyl iodide. 3. Then, intramolecular syn elimination (Ei) through a six-membered transition state.

STEP 1: To a stirred solution of the alcohol (50 μmol, 1.0 eq) , CS2 (4.0 eq) in THF (5 mL) at 0 ºC was added NaH (60% dispersion in mineral oil, 4.0 eq). The resulting mixture was stirred at room temperature for 5 h before MeI (4.0 eq) was added. The reaction was stirred for an additional 10 min before quenched with NH4Cl. The layers were separated, and the aqueous layer was extracted with EtOAc. The combined organic layers were dried (Na2SO4) and concentrated in vacuo to afford the crude product.

STEP 2: A stirred solution of the xanthate (crude, obtained above) in o-DCB (5 mL) was warmed to 150 ºC and stirred for 20 h before cooled to room temperature and MeOH (5 mL) and p-TsOH•H2O (2.0 eq) were added. The resulting mixture was warmed to 30 ºC and stirred for 36 h before diluted with EtOAc and quenched with NaHCO3. The layers were separated, and the aqueous layer was extracted with EtOAc. The combined organic layers were dried (Na2SO4) and concentrated in vacuo. Flash column chromatography afforded the desired alkene.