Boronic derivatives are one of the most successful and important reagents in organic synthesis. Kabalka discovered a remarkable property of dicyclo-hexylborane. This reagent rapidly hydroborates functionalized terminal alkynes without reduction of functional groups. Only aldehydes show any reduction, typically less than 15%. We discovered the auxiliary cyclohexyl groups could be selectively removed by reductive alkylation with two equivalents of p-benzoquinone. The formed boronic esters are directly converted and isolated as the corresponding functionalized alkenyltrifluoroborate salts in very good yields. This route does not require additional steps of protection and deprotection, except for acidic groups. We will explore the scope of this reaction to prepare various functionalized alkenytrifluoroborate salts. Examples cross-coupling reactions will also be presented as a demonstration of their utility.

Preparation of functionalized alkenyltrifluoroborates compounds via hydroboration of terminal alkynes and applications to cross-coupling reactions

ACS Spring 2022

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