monomesylate

Monomesylate refers to a chemical compound in which a single hydroxyl group has been converted into a methanesulfonate (mesylate) ester. The mesylate group, derived from methanesulfonyl chloride, is a strong leaving group in nucleophilic substitution and elimination reactions, facilitating transformation of alcohols into more reactive alkyl mesylates.

Formation of a monomesylate is typically achieved by reacting an alcohol with methanesulfonyl chloride in the presence of a base such as pyridine or triethylamine, often in an aprotic solvent like dichloromethane at low to moderate temperatures. The process requires moisture control because methanesulfonyl chloride is moisture sensitive. In molecules bearing multiple hydroxyl groups, achieving a true monomesylate can be challenging; selective mono‑mesylation may rely on limiting the equivalents of MsCl, applying protecting groups to other OH groups, exploiting steric differences (e.g., primary versus secondary alcohols), or using controlled addition and reaction times.

Properties and uses: The resulting mesylate ester contains the leaving group –OSO2CH3, which makes the original alcohol a good substrate for SN2 substitutions and certain eliminations. Monomesylates are widely used in organic synthesis to activate alcohols for nucleophilic attack by halides, thiolates, or other nucleophiles, and they can serve as intermediates in the preparation of ethers, alkanes, or more complex motifs. In carbohydrate and natural product synthesis, selective monomesylation helps set up downstream transformations while preserving other functional groups.

Safety and handling: Methanesulfonyl chloride is corrosive and moisture sensitive; appropriate protective equipment and ventilation are required. Mesylates themselves should be handled with care to avoid unnecessary exposure and environmental release.