Electrochemical Fluorination of Vinyl Boronates through Donor‐Stabilized Vinyl Carbocation Intermediates**

Abstract

The electrochemical generation of vinyl carbocations from alkenyl boronic esters and boronates is reported. Using easy-tohandle nucleophilic fluoride reagents, these intermediates are trapped to form fully substituted vinyl fluorides. Mechanistic studies support the formation of dicoordinated carbocations through sequential single-electron oxidation events. Notably, this electrochemical fluorination features fast reaction times and Lewis acid-free conditions. This transformation provides a complementary method to access vinyl fluorides with simple fluoride salts such as TBAF.

A Unified Synthetic Strategy to Introduce Heteroatoms via Electrochemical Functionalization of Alkyl Organoboron Reagents

“…Based on the assembled information from the electrochemical assessments, a plausible mechanistic scenario was proposed (Scheme ). The overall process commences with the reaction of organotrifluoroborate to undergo two sequential single-electron oxidations with a concomitant cleavage of the C–B bond via an electron transfer–chemical reaction–electron transfer (ECE) type mechanism at the anode of the cell. , The process presumably involves a transient formation of a radical species, which can be rapidly subjected to further oxidation to the carbocation. The highly reactive cationic intermediate should proceed with C­(sp 3 )–heteroatom bond formation reaction to provide the product.…”

“…Of the numerous oxidation strategies available, the electrochemically mediated process should deliver the required reactive intermediate in the most efficient and regulated fashion . Among various organoboron reagents, organotrifluoroborates were selected as the ideal form of reaction partner because of (a) their stability, which makes them a critical element of a robust synthetic platform, and (b) their anodically active nature, which renders them an efficient unaided electroauxiliary. − Particularly inspiring is the fact that it is a suitable precursor for electrochemical activation, as demonstrated in the studies of Fuchigami and Stahl. ,− , As such, it is anticipated that a chemoselective exploitation of the electrochemical susceptibility of organotrifluorobotates should provide a powerful synthetic platform to solve important synthetic problems with respect to the general introduction of heteroatoms at a sterically hindered C­(sp 3 ) center.…”

Electrochemical synthesis and transformation of organoboron compounds

“…Recently, Nelson and Houk achieved the electrochemical fluorination of vinyl boronic esters with simple fluoride reagents to access vinyl fluorides (Scheme 23b). 60 Mechanistic studies indicated that dicoordinated vinyl carbocations were formed through sequential single-electron oxidation, which was trapped using nucleophilic fluoride reagents to form fully substituted vinyl fluorides. This electrochemical fluorination features short reaction times and provides a practical strategy to access useful fully substituted vinyl fluorides.…”

Cu-catalyzed cascade difluoroalkylation/5-endocyclization/β-fluorine cleavage of ynones

“…In this respect, the direct monofluoroalkenylation of cyclopentanones 2 and fluorination of alkenes, 3 represent the most common methods to access α-monofluoroalkenyl cyclopentanes (Scheme 1). However, these methods require the pre-preparation of cyclopentane-derived starting materials.…”