Alkynylation of Thiols with Ethynylbenziodoxolone (EBX) Reagents: α- or β- π‑Addition?

The alkynylation
of thiols with EthynylBenziodoXolone (EBX) reagents
is a fast and chemoselective method for the synthesis of thioalkynes.
Combined experimental and computational studies are reported, which
led to the identification of a new mechanism for this reaction, proceeding
via an initial sulfur–iodine interaction followed by β-addition,
α-elimination, and a 1,2-shift. Depending on the substituent
on the alkyne, this mechanism can be favored over the previously disclosed
concerted α-addition pathway.