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(a)
Me
Me
Colloid
OMe
H
2
OMe
50
(b)
Me
Me
OMe
OMe
Colloid
H
2
51
Scheme 8.7
Hydrogenation of anisole derivatives.
better dispersed nanoparticles that are more soluble in organic media and more
actives in hydrogenation. Moreover, the Ru/
49a
nanocatalyst provides high activity
and diastereoselectivity (
cis/trans
ratio), although no significant enantioselectivity
has been observed [33].
8.3.3
Phosphine Ligands Including Mixed Donor Ligands
The first chiral ligands derived from carbohydrates used in asymmetric hydrogena-
tion were diphosphines. In the late 1970s Sinou and Descotes [7] synthesized
the monophosphines
52
and
53
(Figure 8.8) from d-xylose and d-glucose.
They were all tested in the asymmetric rhodium-catalyzed hydrogenation of
α
-acetamidoacrylic acids. Starting from d-xylose,
Brunner [22] prepared hydroxyl/phosphine
54
and the phosphine/phosphinite
ligand
55.
A new series of furanoside backbone diphosphines,
56-58,
have been developed
and used for the Rh asymmetric hydrogenation of dehydroamino acid and itaconic
acid derivatives (Figure 8.9) [34].
-acetamidocinnamic and
α
D-
xylo
D-
gluco
D-
xylo
PPh
2
O
Ph
2
P
Ph
2
P
OMe
OR
O
O
O
O
O
O
O
O
O
O
54
R=H
55
R=PPh
2
52
53
Figure 8.8
Phosphines
52
-
55.
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