Sulfonation of Alkenes by Chlorosulfuric Acid, Acetyl Sulfate, and Trifluoroacetyl Sulfate

An exploratory study has been made on the reaction of a number of non‐branched alkenes in [D]chloroform as an aprotic solvent, using chlorosulfuric acid as reagent both in the presence and the absence of [D 8 ]1,4‐dioxane as complexing agent. Reaction of cyclopentene ( 1a ) with 1.1 mol‐equiv. of chlorosulfuric acid in [D]chloroform in the presence of 2.2 mol‐equiv. of [D 8 ]1,4‐dioxane at 0 °C yielded quantitatively 1,2‐cyclopentanesultone ( 2a ). Under similar reaction conditions, the linear alkenes 1b – g afforded the corresponding β‐sultones 2b – g . The ClSO 3 H–dioxane complex acted as a sulfonating reagent with the alkenes to yield the corresponding β‐sultones in a syn cycloaddition of SO 3 to the Carbon‐Carbon double bond. In the absence of [D 8 ]1,4‐dioxane the reaction of the linear alkenes 1a – 1k in [D]chloroform with chlorosulfuric acid at –40 °C led to the formation of the sec ‐alkyl chlorosulfates 5a–i , which were formed after initial protonation of the alkene by the strongly acidic ClSO 3 H. Cyclopentyl chlorosulfate ( 5a ) in [D]chloroform at 0 °C was quantitatively converted into 1,2‐cyclopentanesultone ( 2a ). The sec ‐alkyl chlorosulfates 5b – i at 0 °C gave rise to a mixture of the internal trans ‐ and cis ‐β‐sultones 2b – m . Reaction of 1‐octene ( 1g ) with both acetyl sulfate ( 6a ) and trifluoroacetyl sulfate ( 6b ) as reagent in [D]chloroform at –20 °C directly afforded the products 1,2‐octanesultone ( 2g ), and the ( E ) and ( Z ) isomer of 2‐octene‐1‐sulfonic acid ( 4g ).