Chemistry Reference
In-Depth Information
NUCLEOPHILES
BY
2
Ar-BY
2
n
Alk-BY
2
BY
2
n
BY
2
Y=OR, R, X, etc
ELECTROPHILES
n
Alk-X
X
Ar
X
PRODUCTS
n
Scheme 11.1 Typical nucleophiles, electrophiles and products in Suzuki-Miyaura
coupling chemistry.
Over the last few years, this deficiency has begun to be addressed.
8,9
Methods to affect the stereospecific coupling of certain classes of chiral
organoboron nucleophiles have been reported over the last 5 years and de-
velopment continues in this area. In addition, chiral electrophiles have also
shown promise as partners in stereospecific coupling reactions. Finally,
racemic electrophiles have been extensively examined in dynamic kinetic
resolution strategies. This chapter describes recent advances in these three
areas, starting first with stereospecific couplings of chiral, enantioenriched
organoboron species. Advances in cross-coupling reactions that are not of
the Suzuki-Miyaura variant will not be described in this chapter unless they
are critical to the discussion. For these reactions, the reader is referred to
several recent reviews.
8-11
11.2 Chiral Nucleophiles: Stereospecific Suzuki-
Miyaura Cross-Couplings
As early as 1986,
2
primary sp
3
-hybridized boron nucleophiles (1) were shown
to be effective partners in the Suzuki-Miyaura cross-coupling reaction [eqn
(11.1)]. Since that time, this reaction has been employed extensively in the
synthesis of complex organic molecules.
12
The transformation is made even
more useful by the ease of synthesis of the primary borane by simple
hydroboration of the corresponding alkene, usually with 9-BBNH, a reaction
often performed back-to-back with the coupling itself, providing an inter-
esting overall transformation [eqn (11.2)].
13
Other iterations of this reaction
employ primary boronic esters or alternative trialkylboranes.
12-16
[PdCl
2
(dppf)]
NaOH
THF
Ph
Ph
+
9BBN
(11
:
1)
Br
n
Oct
1
2
3
9BBN-H
Pd/Base
Ar-X
9BBN
Ar
R
R
R
(11
:
2)
4
5
6
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