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successfully reacted with Ar-9-BBN coupling partners using a catalyst system
consisting of NiBr
2
-diglyme and 4,4
0
-di-tert-butyl-2,2
0
-bipyridine (150) in the
presence of alkoxide activators. Notably, synthetically useful yields were
obtained in the products of meta-substituted phenyl-9-BBN reagents that are
not otherwise accessible through Friedel-Crafts alkylation procedures.
Although no asymmetric Suzuki-Miyaura couplings of these substrates have
yet been reported, this is an exciting contribution to the field that bears
considerable promise.
(11
:
40)
Finally, in a recent development in the Negishi manifold, Fu and co-
workers have shown that racemic alcohols are also viable partners in the
stereoconvergent Suzuki-Miyaura coupling reaction (Scheme 11.17).
117
Three key features of this approach are (1) the in situ generation of
reactive mesylates, (2) the fact that successful substrates are benzylic and
(3) the use of LiI as an essential additive. Putting these three facts together
along with comparative reactions in which the corresponding benzylic
iodide was employed led the authors to conclude that the reaction actually
X
Ar
-ZnI
Ar
Ph
CH
3
NiBr
2
diglyme/
153
additives, -45 °C
Ph
CH
3
(±)-
152
154
Ph
Ph
O
O
MeO
N
N
OMe
153
Original conditions,
X
, = OH
Additives = MsCl/NEt
3
(first step)
then 4 eq LiI
94% ee, 93% yield
X
, = OMs
One step, 4 eq LiI
X
, = I
One step, 4 eq LiI
X
, = I
One step, no LiI
88% ee, 88% yield
87% ee, 81% yield
87% ee, 49% yield
Scheme 11.17
Stereoconvergent Negishi coupling of in situ-generated iodides.
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