Photoinitiated anti-Hydropentafluorosulfanylation of Terminal Alkynes

A photoinitiated anti -hydropentafluorosulfanylation of terminal alkynes using SF 5 Cl and (TMS) 3 SiH as the hydrogen atom donor is reported. This transformation generates selectively ( Z ) - (1-alken-1-yl)pentafluoro-λ 6 -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 SF 5 -substituted vinylic radicals to adopt a cis geometry, and to increased steric contacts during the transition structures leading to the minor ( E )-products.