Organoboron compounds are widely utilized in organic synthesis and the boronic acid functional group is among the most versatile in chemical transformations. The Suzuki-Miyaura cross-coupling reaction has employed these substrates for otherwise difficult carbon-carbon bond formations with alkenylboronates particularly successful. Therefore, methods for synthesizing functionalized alkenylboronates continue to be a subject of intense investigation. The alkenylboronate moiety plays a vital role in several FDA-approved drugs, polymer science, and as intermediates in commodity chemicals. Fortunately, several transition metal-catalyzed preparations of substituted α,β-unsaturated nitriles and allenoates have been reported. In this presentation, we report an organocatalytic method for the hydroboration of 3-substituted-propiolonitriles and allenoates. In the presence of catalytic amounts of tributylphosphine and pinacolborane, regioselective hydroboration of the internal triple bond of propiolonitriles proceeded in a stereoselective fashion under mild conditions to afford the corresponding (E)-1,2-vinylcyanoborane derivatives. On the other hand, using CuCl and bis(pinacolato)diboron in methanol, a variety of allenoates underwent β-boration, α-protonation in a highly efficient regio- and stereoselective to afford the corresponding Z-β,γ-unsaturated β-boryl esters under mild conditions. We will discuss the development and investigations to elucidate the mechanism of these reactions.

Trans hydroboration of 3-substituted-propiolonitriles and allenoates

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