Chemistry Reference
In-Depth Information
O
O
O
O
Ph
Ph
Ph
Ph
N
P
N
N
P
79
80
Chelucci
ee =20%
l/b = 0/100
Chelucci
ee = 3%
l/b = 0/1 00
O
SiMe
3
O
N
i
Pr
i
Pr
N
Fe
SiMe
3
Fe
PPh
2
PPh
2
(
S,Sp
)-
81
(
S,Rp
)-
82
Chan
ee = 45%
l/b = 21/79
Chan
ee = 28%
l/b = 1/> 99
Figure 10.18.
P - N ligands
79
-
82
used alkoxycarbonylation reactions.
that have been used in the methoxycarbonylation of vinylarenes is shown in Figure 10.19.
The use of the neomenthyldiphenylphosphine
83
(NMDPP) (Fig. 10.19) in the asym-
metric methoxycarbonylation of styrene yielded 52% ee using Pd(dba)
2
as precursor in
the presence of trifl uoroacetic acid at 50°C under atmospheric pressure of CO [64].
Ligand NMDPP
83
was also used in the asymmetric alkoxycarbonylation of styrene
using a biphasic solvent system formed by an ionic liquid and an organic phase contain-
ing isopropanol [65]. By using the catalytic system PdCl
2
(NCPh)
2
- NMDPP -
p
- TsOH,
high chemo- and regioselectivities were obtained, but only enantioselectivity up to 5%
could be achieved. In 1990, Alper and Hamel reported high enantioselectivity (91% ee)
and total regioselectivity to the branched acid (64% of isolated yield) using the PdCl
2
-
CuCl
2
- HCl -
84
(BNPPA) system (Fig. 10.19) for the hydroxycarbonylation of 2-vinyl-6-
methoxynaphtalene under 1 atm of a mixture of CO and O
2
at room temperature [66].
When
p
-isobutylstyrene was used as the substrate, the same catalytic system afforded
84% ee under the same conditions. By using the same ligand, the methoxycarbonylation
of styrene was recently reported by Yang and Jiang, but only 38% ee was achieved under
identical conditions [67] .
In 1997, Nozaki and coworkers used the (S,S)-phospholane ligand
85
(Fig. 10.19 ) [61] ,
but, although this system afforded high regioselectivity, the enantioselectivity was very
low (2%). Later, the same authors reported on the application of palladium complexes
with binaphthol - derived phosphines
86
(Fig. 10.19) in the methoxycarbonylation of
2 - vinyl - 6 - methoxynaphthalene. By using a catalytic system formed by PdCl
2
and 2 equiv-
alents of
85
under 30 atm of CO at 40°C, 53% of ee were achieved for the branched
ester, (S)-naproxen methyl ester, as the only reaction product [68]. In 2005, Claver and
coworkers reported the fi rst use of isolated Pd chiral monophosphine species in this
