Bis(pinacolato)diboron

Introduction

Since Brown’s discovery of the hydroboration reaction, ­organoboron compounds have found wide application in organic synthesis. [1] The synthesis of functional organoboranes has mostly relied on either the hydroboration of unsaturated hydrocarbons or the transmetallation between an organometallic precursor and an appropriate boron compound.

In 1993, Miyaura’s group reported the first platinum(0)-catalyzed vic-diboration of alkynes using bis(pinacolato) di­boron (1). [2] This group subsequently expanded the substrates to alkenes, 1,3-dienes, allenes, and a,b-unsaturated ketones. [3] These reactions provide new alternatives to access the funcational organoboron compounds and also popularized diboron 1 as a new boron source.

B₂pin₂ is used preferentially over other (alkoxo)diborons, because both the borylated products derived from it and itself can be handled in air and exhibit high stability towards hydrolysis, which facilitate reaction workup and purification. B₂pin₂ is commercially available from Aldrich, Lancaster, Frontier Scientific Inc, etc.

Besides the Pt-mediated vic-diboration of unsaturated hydrocarbon, B₂pin₂ undergoes coupling reactions with aryl halides and allyl acetates, in the presence of Pd catalysts, to give aryl and allyl boronates. [4] [5] More recently, B₂pin₂ has been used in the borylation of alkanes and arenes via Rh- and Ir-mediated C-H activations. [6] [7] Futhermore, B₂pin₂ has found application in carbenoid chemistry, which has been explored by Hiyama’s group, to generate gem-diborylated alkenes. [8]

The borylated products derived from the above-mentioned strategies serve as versatile synthetic intermediates, which can undergo oxidation, allylation, and Suzuki-Miyaura cross-coupling reaction to generate more complex organic frameworks.

References

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• 1b Matteson DS. Stereodirected Synthesis with Organoboranes   Springer-Verlag; Berlin: 1995. 
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