Chemistry Reference
In-Depth Information
D-
gluco
OAc
OAc
OAc
D-
gluco
AcO
O
OAc
OAc
OAc
S
AcO
O
S
PR
2
Fe
PPh
2
29
30a
R= Ph
30b
R= Cy
Figure 10.14
Thioether-phosphine ligands
29
and
30.
D-
gluco
OPiv
D-
altro
PPh
2
O
Ph
O
PivO
O
S
t
Bu
O
PivO
S
t
Bu
N
OAc
PPh
2
31
32
Figure 10.15
Phosphine-thioether ligands
31
and
32.
D-
xylo
O
S
PPh
2
O
O
O
33
Figure 10.16
Phosphine-oxathiane ligand
33.
the thiosugar moiety was the sole stereogenic unit on ligand
30
(Figure 10.14),
enantioselectivities were only moderate (up to 64% ee) [23b].
Khiar and coworkers reported the successful use of phosphine-thioether
ligand
31
(Figure 10.15) in the Pd-catalyzed asymmetric allylic alkylation of 1,3-
diphenylprop-2-enyl acetate (
S1
) [yields up to 82% and up to 90% ee,
(S)
] [24a].
The same group also reported the application of ligand
32
(Figure 10.15), but with
little success [yields up to 55% and up to 30% ee,
(R)
] [24b].
In 2003, a phosphine-oxathiane ligand
33,
derived from d-(
)-xylose, was devel-
oped for Pd-catalyzed allylic substitution reactions (Figure 10.16). Good enantiose-
lectivities were obtained in the addition of dimethyl malonate and benzylamine
to 1,3-diphenylprop-2-enyl acetate (
S1
) [ees up to 91%
(S)
and 94%
(R)
, respec-
tively] [25].
More recently, a series of phosphinite-thioether ligands with a furanoside back-
bone,
34a-g,
were easily prepared from d-xylose (Scheme 10.12). These ligands
were applied in the Pd-catalyzed allylic substitution of mono- (
S6
and
S7
) and
disubstituted (
S1-S3
) linear and cyclic (
S4
and
S5
) substrates (up to 95% ee)
+
Search WWH ::
Custom Search