Chemistry Reference
In-Depth Information
difluorphos
Aryl/Heteroaryl Chlorides
O
F
Ni(COD)
2
(5 - 10 mol %)
Ligand (6 - 12 mol %)
NaO
t
-Bu
O
O
R
F
R
O
PPh
2
PPh
2
ArCl
Ar
toluene, 60 - 80 °C
O
F
n
n
75 % avg. yield
up to 99 % ee
R = Me, Et, Bn
n = 0, 1
F
O
Ligand = BINAP or difluorphos
Aryl Triflates
[M] (5 - 10 mol %)
difluorphos (6 - 12 mol %)
NaO
t
-Bu
O
O
Me
Me
ArOTf
Ar
toluene, 60 - 100 °C
[M] = Pd, Ni
n
n
up to 85 % yield
up to 98 % ee
Figure 2.64 Asymmetric a-arylations of ketones with BINAP- or difluorphos-based
catalysts.
(
R
)-P-Phos
OMe
Ni(COD)
2
(2 mol %)
(
R
)-P-Phos (2.4 mol %)
NaO
t
-Bu
toluene, 100 °C
O
O
N
Me
Me
ArBr
Ar
MeO
MeO
PPh
2
PPh
2
n
n
up to 90 % yield
up to 98 % ee
N
OMe
Figure 2.65 Asymmetric a-arylations using an (R)-P-Phos-based nickel catalyst.
Suzuki-Miyaura reactions
218
and promote intramolecular asymmetric dear-
omatization reactions of naphthalenes (Figure 2.67).
219
Ligands that are stereogenic at phosphorus have also been used in
asymmetric cross-coupling reactions. For instance, Hamada and Buchwald
developed monophosphine ligands that contain both axial chirality and
central chirality at phosphorus (Figure 2.68).
220
It was found that this ligand
was effective for highly asymmetric a-vinylation of a ketone enolate, but
significantly less so for corresponding a-arylation.
This P-stereogenic ligand, however, was broadly effective in Pd-catalyzed
highly enantioselective a-arylation and a-vinylation of oxindoles, as reported
by Buchwald and co-workers.
221
Furthermore, the same group also demon-
strated that asymmetric dearomative spirocyclization of phenols can be
promoted by a Pd catalyst containing this P-stereogenic ligand with good to
high enantiocontrol (Figure 2.69).
222
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