Introduction
<P>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.
</P><P>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. </P><P>B
2pin
2 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. B
2pin
2 is commercially available from Aldrich, Lancaster, Frontier Scientific Inc, etc.</P>
<P>Besides the Pt-mediated
vic-diboration of unsaturated hydrocarbon, B
2pin
2 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, B
2pin
2 has been used in the borylation of alkanes and arenes via Rh- and Ir-mediated C-H
activations.
[
6]
[
7]
Futhermore, B
2pin
2 has found application in carbenoid chemistry, which has been explored by Hiyama’s
group, to generate
gem-diborylated alkenes.
[
8]
</P><P>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.</P>
