6-Iodo-1-hexene
While in its traditional form the Finkelstein reaction involves the transformation of an alkyl chloride or bromide to the corresponding alkyl iodide via treatment with sodium iodide in acetone, the name also refers to the conversion of alkyl sulfonates to alkyl iodides. Alkyl sulfonates are readily prepared from alcohols.
Procedure:
A solution of 5-hexen-1-ol (5.0 g, 0.050 mol) and triethylamine (7.6 g, 0.076 mol) in 250 mL of dichloromethane is cooled under inert atmosphere in an ice salt bath to ca. -5 °C. Methanesulfonyl chloride (4.7 mL, 0.06 mol) is added dropwise with stirring. After stirring for an additional hour at ca. -5 °C, the reaction is washed with cold water, cold 10% aqueous hydrochloric acid, a cold saturated aqueous solution of sodium bicarbonate, and a cold solution of brine using approximately 75 mL for each wash. The organic fraction is dried over anhydrous magnesium sulfate, filtered, and concentrated in vacuo to afford the mesylate which is used in the next step without further purification.
To the flask containing the unpurified mesylate product are added 100 mL of dry acetone followed by anhydrous sodium iodide (9.3 g, 0.06 mol) with stirring under inert atmosphere. After stirring at reflux for 4 hours the reaction mixture is cooled to ambient temperature. The resulting solution is concentrated in vacuo and treated with 25 mL of pentane and 25 mL of 10 % aqueous sodium thiosulfate. The organic fraction is washed with 25 mL of brine, dried over magnesium sulfate, filtered, and concentrated in vacuo. The resulting crude material is then passed through a plug of silica gel and eluted with pentane. The solution is then concentrated in vacuo to afford the title compound.