Dimesylates

Dimesylates are chemical species that contain two methanesulfonate (mesylate, MsO–) groups. In practice, the term is used for two related classes: bis(methanesulfonate) esters formed when both reactive sites of a diol are converted to mesylate esters, and salts in which a dipositive substrate such as a diamine is paired with two mesylate counterions. The common feature is two MsO– substituents, which are strong leaving groups in nucleophilic substitution reactions.

Preparation typically involves converting a diol to its dismesylate by treating with two equivalents of methanesulfonyl chloride in a base such as pyridine or triethylamine. For amine-containing substrates, reaction with methanesulfonic acid yields the corresponding dimesylate salt, or the base can be used to form the disubstituted mesylate derivative. Dry conditions are often required to prevent hydrolysis of the mesylate groups.

Reactivity of dimesylates centers on the mesylate groups as excellent leaving groups, enabling sequential substitutions at two sites. This makes dimesylates useful in complex organic synthesis where two activation points are needed, such as constructing extended carbon skeletons, enabling cyclizations, or preparing multifunctional intermediates that can be displaced by nucleophiles including alkoxides, thiolates, or amide anions.

Examples include bis(methanesulfonate) derivatives of diols or diamines, sometimes referred to as the dismesylates of the corresponding diol or diamine. These compounds are typically used under anhydrous conditions in organic solvents and are handled with standard laboratory safety practices for reactive sulfonate esters.

See also: mesylate, methanesulfonyl chloride, sulfonate esters.