Photoinitiated anti-Hydropentafluorosulfanylation of Terminal Alkynes

A photoinitiated anti-hydropentafluorosulfanylation of terminal alkynes using SF₅Cl and (TMS)₃SiH as the hydrogen atom donor is reported. This transformation generates selectively (Z)-(1-alken-1-yl)pentafluoro-λ⁶-sulfanes (Z:E : >85:15), thus allowing the preparation of this previously unknown geometrical isomer. DFT calculations highlight that the selectivity is due to the intrinsic preference of SF₅-substituted vinylic radicals to adopt a cis geometry, and to increased steric contacts during the transition structures leading to the minor (E)-products.