Tetrafluoroborate Salt Fluorination for Preparing Alkyl Fluorides

Stereodivergent Alkyne Hydrofluorination Using a Simple Practical Reagent

“…We next explored the scope of alkyl substituents on the substrate. A range of primary, secondary, cyclic or acyclic alkyl-substituted alkynes could be employed in the hydrofluorination to furnish respective products again with moderate to good yields and excellent regio-and stereoselectivities (27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39). Remarkably, substrates with potentially sensitive functional groups including a primary chloro, a carboxymethyl, a cyano, a pyridyl, and a phthalimido group also delivered the monofluoroalkene products, highlighting the mildness and good functional group tolerance of this protocol (40)(41)(42)(43)(44)(45)(46).…”

“…Considering their low cost, high fluoride content, as well as excellent safety, stability, and handling profiles, tetrafluoroborate (BF 4 − ) salts are particularly attractive sources of nucleophilic fluoride 29 . However, aside from the well-developed Balz-Schiemann process, they have seldom been employed in the formation of C(sp 2 )−F bonds due to the weak nucleophilicity of this anion, and known methods often require the use of exotic functional groups or strongly oxidizing conditions 30 .…”

Stereodivergent Alkyne Hydrofluorination Using a Simple Practical Reagent

“…Among a collection of We next explored the scope of alkyl substituents on the substrate. A range of primary, secondary, cyclic or acyclic alkyl-substituted alkynes could be employed in the hydrofluorination to furnish respective products again with moderate to good yields and excellent regio-and stereoselectivities (27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39). Remarkably, substrates with potentially sensitive functional groups including a primary chloro, a carboxymethyl, a cyano, a pyridyl, and a phthalimido group also delivered the monofluoroalkene products, highlighting the mildness and good functional group tolerance of this protocol (40)(41)(42)(43)(44)(45)(46).…”

Stereodivergent Alkyne Hydrofluorination Using Protic Tetrafluoroborates as Tunable Reagents

“…Considering their low cost, high fluoride content, as well as excellent safety,stability,and handling profiles,tetrafluoroborate (BF 4 À )s alts are particularly attractive sources of nucleophilic fluorine. [16] However,aside from the well-developed Balz-Schiemann process,t hey have seldom been employed in the formation of C(sp 2 )ÀFb onds because of the weak nucleophilicity of this anion, and the handful of examples in which they are employed as fluorine sources in vinyl fluoride synthesis generally entail the use of either exotic functional groups or strongly oxidizing conditions. [17] Given the canonical status of the alkyne hydrochlorination, hydrobromination, and hydroiodination reactions, [18a] and mechanistic studies supporting either ac oncerted Ad E 3 mechanism or an Ad E 2m echanism featuring av inyl cation intermediate for these processes, [18b,c] we hypothesized that am etal-free hydrofluorination could result from am ild and selective protonation of the alkyne,f ollowed by trapping of the resultant Brønsted acid-alkyne complex or vinyl cation intermediate by BF 4 À .T herefore,w ep osited that as uitable fluoroboric acid (HBF 4 )e quivalent could serve as ag eneral and practical hydrofluorinating reagent for alkynes.…”