Potassium organotrifluoroborates have emerged as a suitable alternative to boronic acids and boronate esters, owing to their air- and water stability, low toxicity and functional group compatibility. Although recent attention has been paid to the reactivity of potassium alkyltrifluoroborates (particularly in the Suzuki-Miyaura cross-coupling reaction), their preparation has been studied to a lesser extent. Classic preparation methods involve hydroboration or the reaction of alkyllithium and alkylmagnesium reagents with suitable boron compounds. However, these methods suffer from a poor substrate scope and functional-group tolerance. We examined new methods that allow rapid access to new classes of potassium alkyltrifluoroborates. In the interest of maximizing atom economy, we investigated diboron reagents that could bypass the pinacol ester intermediate. Tetrahydroxydiboron  (B2(OH)4) proved to be efficient  in the copper-catalyzed borylation of alkyl electrophiles, allowing direct, efficient access to alkyl boronic acids and potassium trifluoroborates. The results obtained from these studies and other developments will be discussed.

Direct synthesis of potassium alkyltrifluoroborates from alkyl halides

244th National Meeting (2012)

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