Overcoming a Radical Polarity Mismatch in Strain‐Release Pentafluorosulfanylation of [1.1.0]Bicyclobutanes: An Entryway to Sulfone‐ and Carbonyl‐Containing SF₅‐Cyclobutanes

Abstract

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 sulfone‐based BCBs are detailed herein, as well as proof‐of‐concept that the logic extends to tetrafluoro(aryl)sulfanylation, tetrafluoro(trifluoromethyl)sulfanylation, and three‐component pentafluorosulfanylation reactions. The methods presented enable isolation of both syn and anti isomers of SF5‐CBs, but we also demonstrate that this innate selectivity can be overridden in chloropentafluorosulfanylation; that is, an anti‐stereoselective variant of SF5Cl addition across sulfone‐based BCBs can be achieved by using inexpensive copper salt additives. Considering the SF5 group and CBs have been employed individually as nonclassical bioisosteres, structural aspects of these unique SF5‐CB “hybrid isosteres” were then contextualized using SC‐XRD. From a mechanistic standpoint, chloropentafluorosulfanylation ostensibly proceeds through a curious polarity mismatch addition of electrophilic SF5 radicals to the electrophilic sites of the BCBs. Upon examining carbonyl‐containing BCBs, we also observed rare instances whereby radical addition to the 1‐position of a BCB occurs. The nature of the key C(sp3)–SF5 bond formation step – among other mechanistic features of the methods we disclose – was investigated experimentally and with DFT calculations. Lastly, we demonstrate compatibility of SF5–CBs with various downstream functionalizations.

Oxidative Difunctionalization of N-Aryl Bicyclobutyl Amides with Aldehydes: Divergent Synthesis of Acylated and Alkylated 3-Spirocyclobutyl Oxindoles

“…Bicyclo[1.1.0]­butane (BCB), a representative small carbocycle with substantial strain energy, has been regarded as a valuable building block for the construction of versatile cyclic scaffolds through the strain-release-driven functionalization of the interbridgehead C–C bond in BCBs. , Classical protocols are mainly focused on the hydrofunctionalization of BCBs with polar reagents and radicals. , To expand the applications of strain-release chemistry in organic synthesis, leveraging highly strained BCBs to perform the difunctionalization of C–C σ bonds is desirable. Currently, a few examples of difunctionalization of BCBs have been established. , For example, Mykhailiuk and Anderson reported a halosulfonylation of BCBs with sulfinate salts and halogen reagents in the presence of catalytic Et 3 B (Scheme a) . In addition, photoinduced difunctionalizations of BCBs with a diverse array of functional reagents have been successfully achieved (Scheme b). ,, Despite all these noteworthy advancements, reports of dicarbofunctionalization of BCBs remains scarce …”