Strain-Release Pentafluorosulfanylation of [1.1.0]Bicyclobutanes: An Entryway to Achiral SF5-Cyclobutanes

The first assortment of achiral pentafluorosulfanylated cyclobutanes (SF5-CBs) are now synthetically accessible through strain-release functionalization of [1.1.0]bicyclobutanes (BCBs) using SF5Cl. Methods for both chloropentafluorosulfanylation and hydropentafluorosulfanylation of BCBs are detailed herein, as well as proof-of-concept that the logic extends to tetrafluoro(aryl)sulfanylation, tetrafluoro(trifluoromethyl)sulfanylation, and iodopentafluorosulfanyl-ation. Considering the SF5 group and CBs have been employed as nonclassical bioisosteres, structural aspects of these unique SF5-CB “hybrid isosteres” were also studied using SC-XRD. Ostensibly, the reaction proceeds through a curious polarity mismatch addition of SF5 radicals to the electrophilic sites of the BCBs. The nature of the C(sp3)–SF5 bond formation step was studied and contextualized using DFT calculations.