Chemistry Reference
In-Depth Information
ents at the 6-position (R
2
) were detrimental on the reaction, probably due to steric
effects (entries 7 and 8).
-Donor groups in the 4-position favored the formation of the
branched product in high yields (entries 3-5), while the introduction of an electron-
withdrawing NO
2
group (entry 6) resulted in a signifi cant drop in yield [215a].
Other substituted cinnamyl substrates as well as the isomeric branched substrates
gave comparable results, indicating a fast equilibration of the isomeric Mo-allyl com-
plexes involved (Fig. 8B.23) [215b]. The especially high regioselectivity obtained with the
4 - amino - substituted ligand
L44c
forced the development of a recyclable resin-supported
ligand
L43b
, which gave comparable results to
L44c
(entry 9) [216].
Meanwhile, a wide range of ligands based on the parent structure
L43a
(Fig. 8B.22 )
have been developed and investigated by Trost, Hughes, and others [217], and Ko
π
ovsk ý
et al. [218]. Their results are collected in Table 8B.32. To get further information about
the binding mode of this multidentate ligands, in initial studies, Trost et al. replaced one
picolinamide unit with a nicotinamide group (
L43c
) (entry 3).
Surprisingly, the yield and selectivities were slightly better than those obtained with
standard ligand
L43a
(entries 1 and 2), although the reaction was slower. The nitrogen
č
TABLE 8B.32. Asymmetric Allylations with Pyridylamide Ligands L43a - k
OCO
2
Me
Ph
MeO
2
C
CO
2
Me
+
l
NaCH(CO
2
Me)
2
CO
2
Me
or
Ph
Precatalyst,
L*
Ph
CO
2
Me
OCO
2
Me
Ph
b
Product
Entry
Substrate
Ligand
Precatalyst
Yield (%)
b
:
l
ee (%)
1
l
L43a
( C
7
H
8
)Mo(CO
3
)
90
28:1
99 (
S
)
2
b
L43a
(EtCN)
3
Mo(CO)
3
70
13:1
92 (
S
)
3
l
L43c
( C
7
H
8
)Mo(CO
3
)
93
46:1
99 (
R
)
4
l
L43d
( C
7
H
8
)Mo(CO
3
)
90
60:1
99 (
R
)
5
b
L43d
( C
7
H
8
)Mo(CO
3
)
90
53:1
92 (
R
)
6
l
L43e
( C
7
H
8
)Mo(CO
3
)
35
1:1
24 (
R
)
7
l
L43f
(EtCN)
3
Mo(CO)
3
29
19:1
98 (
S
)
8
l
L43g
( C
7
H
8
)Mo(CO
3
)
95
30:1
99 (
R
)
9
l
L43h
( C
7
H
8
)Mo(CO
3
)
95
19:1
99 (
S
)
1 0
l
L43i
(EtCN)
3
Mo(CO)
3
64
8:1
92 (
S
)
1 1
b
L43i
(EtCN)
3
Mo(CO)
3
72
12:1
88 (
S
)
1 2
l
L43j
(EtCN)
3
Mo(CO)
3
69
13:1
89 (
R
)
1 3
b
L43j
(EtCN)
3
Mo(CO)
3
68
13:1
74 (
R
)
1 4
l
L43k
(EtCN)
3
Mo(CO)
3
68
32:1
98 (
R
)
1 5
b
L43k
(EtCN)
3
Mo(CO)
3
59
38:1
97 (
R
)
