Vinyl, from thiols addition alkynes

Thiol-yne radical reactions follow a similar initiation step to that of thiol-ene reactions. After the initial addition of a thiol to the alkyne and formation of a vinyl radical with a P-thioether function, a hydrogen abstraction from another thiol molecule generates a new thiyl radical. Subsequent addition of a thiyl radical on the vinyl thioether forms another carbon radical, which abstracts a hydrogen from another thiol molecule to give a 1,2-dithioether, and the thiyl radical generated reenters the chain process (Scheme 1.11). The addition of the first thiol to the alkyne is the rate-limiting step, and the second thiol addition to the intermediate thiol-alkene is a faster step. Studies revealed that the second addition is approximately three times faster than the first addition [45]. 

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