Photoinitiated anti-Hydropentafluorosulfanylation of Terminal Alkynes.

A photoinitiated anti-hydropentafluorosulfanylation of terminal alkynes using SF5 Cl and (TMS)3 SiH 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.