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HO
HO
HO
OH
OH
OPAr
2
HO
R
R
O
(a)
(b)
(c)
O
O
O
OH
R
OH
R
NH
2
OH
OH
OPAr
2
25a-h
OH
OH
OH
HO
OH
HO
R
Ar
2
PO
R
(3)
(d)
(2)
O
O
O
HO
R
R
OH
OH
OH
OH
OH
OPAr
2
26a-h
Scheme 8.5
Synthesis of ligands
25
and
26:
(a) (1) H
2
O; (2) NaNO
2
/AcOH,
T
<
2 °C; (3)
NaBH
4
/H
2
O (80% overall yield); (b) RCl/
DMF/imidazole or RCl/CH
2
Cl
2
/Py (70-72%
yield); (c) Ar
2
PCl/CH
2
Cl
2
/NEt
3
(60-91%
yield); (d) (1) xylene/methanesulfonic acid;
(2) acetone/H
2
SO
4
; (3) THF/H
2
O, Amberlite
IR-120 (H
+
) (3% overall yield).
Table 8.2
Hydrogenation of unsaturated esters and imines with diphosphinite ligands
25
-
27.
Entry
Product
Ligand
Conversion (%)
ee (%)
Ph
1
25b
96
81
(R)
2
26b
100
59
(R)
MeO
2
C
*
2b
NHAc
3
27
100
27
(R)
4
25b
100
85
a)
(R)
5
25c
100
87
b)
(R)
MeO
2
C
*
2d
NHAc
6
26b
100
59
(R)
7
27
100
18
(R)
8
25a
100
48
(S)
9
26a
100
53
(R)
CO
2
Me
MeO
2
C
*
4b
10
26b
100
9
(R)
11
27
100
4
(R)
Ph
H
*
6a
12
25f
100
70 (
+
)
Bn
H
*
6b
13
25h
97
76 (
−
)
a)
91% ee at
−
25 °C.
b)
93% ee at
−
25 °C.
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