Tosylates, Mesylates, and Triflates Leaving Group Derivatives of Alcohols

10 Tosylates, Mesylates, and Triflates Leaving Group Derivatives of Alcohols 

The hydroxyl group of an alcohol can be converted to a good leaving group by conversion to a sulfonate ester derivative. The most common sulfonate esters used for this purpose are methanesulfonate esters ( mesylates ), p-toluenesulfonate esters ( tosylates ), and tri-fiuoromethanesulfonates ( triflates ). 

The desired sulfonate ester is usually prepared by reaction of the alcohol in pyridine with the appropriate sulfonyl chloride, that is, methanesulfonyl chloride (mesyl chloride) for a mesylate, p-toluenesulfonyl chloride (tosyl chloride) for a tosylate, or trifluoromethane-sulfonyl chloride [or trifluoromethanesulfonic anhydride (triflic anhydride)] for a triflate. Pyridine (C5H5N, pyr) serves as the solvent and to neutralize the HCI formed. Ethanol, for example, reacts with methanesulfonyl chloride to form ethyl methanesulfonate and with p-toluenesulfonyl chloride to form ethyl p-toluenesulfonate  

A method for making an alcohol hydroxyl group into a leaving group. 

It is important to note that formation of the sulfonate ester does not affect the stereochemistry of the alcohol carbon, because the C—O bond is not involved in this step. Thus, if the alcohol carbon is a chirality center, no change in configuration occurs on making the sulfonate ester—the reaction proceeds with retention of configuration. On reaction of the sulfonate ester with a nucleophile, the usual parameters of nucleophilic substitution reactions become involved. 

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TOSYLATES, MESYLATES, AND TRIFLATES LEAVING GROUP DERIVATIVES OF ALCOHOLS... 

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