tosyl

Tosyl is the name given to the p-toluenesulfonyl group, a sulfonyl substituent derived from p-toluenesulfonic acid. The group, commonly abbreviated as Ts, consists of a para-methylbenzenesulfonyl moiety connected through the sulfonyl center to another atom, most often nitrogen or oxygen in organic substrates. The term also refers to related reagents and derivatives, including p-toluenesulfonyl chloride (TsCl) and p-toluenesulfonic acid (TsOH).

In organic synthesis, tosylation refers to reactions that install the tosyl group. A key application is the conversion of alcohols to tosylates (R–OTs) using TsCl or related reagents. Tosylates are excellent leaving groups, facilitating nucleophilic substitution to form a wide range of products, such as halides, ethers, or amines. The tosylate strategy is widely used to activate alcohols for substitution while keeping other functional groups intact.

The tosyl group is also a popular protecting group for amines. Amines can be protected by converting them to N-tosyl derivatives (R–NH–Ts), which are stable under many conditions and can be selectively deprotected later in a synthetic sequence. Introduction of the N-tosyl protection is typically achieved with TsCl in the presence of a base, whereas deprotection requires specific conditions that depend on the substrate.

Common related reagents include TsCl, used for tosylation, and TsOH, the free acid form used in various catalytic or acid-promoted contexts. The tosyl framework is favored for its balance of stability during synthesis and controllable deprotection in the final stages of a sequence.