Chemistry Reference
In-Depth Information
CHO
catalyst (0.2 mol%): Rh(acac)(CO)
2
/ligand* (ratio 1:2)
*
selectivity for
branched product
2
>90%
H
2
, CO, toluene
Me
X
X
1
2
O
O
R
2
R
1
P
P
TBDPSO
O
O
Me
O
O
O
O
O
O
O
=
44
45
Me
OTBDPS
O
O
O
O
O
P
O
P
O
R
2
R
1
R
1
= R
2
=
t
Bu
b
b
b
57%
41% ee (S)
98%
14% ee (R)
19% ee (R)
X = H
X = H
X = H
R
1
=
t
Bu, R
2
= OMe
c
b
60%
49% ee (S)
X = F
c
98%
b
34%
60% ee (S)
X = OMe
c
64%
30% ee (S)
X = H
O
O
O
P
O
P
O
OTBDPS
O
Me
O
P
O
O
O
O
O
46
47
48
TBDPSO
Me
O
O
O
O
O
O
P
P
P
O
O
O
b
b
X = H
X = H
57%
22% ee (R
)
X = H
X = H
33%
17% ee (S)
18% ee (S)
b
43%
26% ee (R)
34% ee (R)
X = H
X = H
c
40%
43% ee (R
)
c
25%
c
38%
Scheme 9.7
Asymmetric hydroformylation of styrene and derivatives with
C
2
-symmetric
carbohydrate phosphite ligands.
enantiomeric products). With substituted styrenes, the ee increased slightly for
ligand
44b.
9.1.2
Diphosphinite Ligands
While bidentate carbohydrate phosphinite ligands are highly successful in asym-
metric hydrogenation reactions, they have only met with rather limited success in
asymmetric hydroformylation. The group of RajanBabu [16] reported the use of
d-
gluco
configured ligands
49
carrying substituted phenyl residues on the phos-
phinite donor sites in the reaction with vinyl-naphthalenes as substrates (Scheme
9.8). The efficiency of the asymmetric discrimination with ligands
49
turned out
to be highly sensitive to the solvent and the nature of the substituents on the
phosphinite donors. The highest ee values were achieved in apolar solvents such
as hexane and with ligand
49b
containing electron-withdrawing CF
3
groups, while
polar solvents such as THF and electron-donating substituents on the phosphinite
Search WWH ::
Custom Search