Chemistry Reference
In-Depth Information
Ts
Bn
OCO
2
Me
Rh(PPh
3
)
3
Cl
N
Ts
Bn
+
P(OMe)
3
Li
Ph
Ph
THF
8
9
(87%, >99% ee)
Regioselectivity (19:1)
Scheme 5.3.
R
1
R
2
NH
NR
1
R
2
[Ir(COD)Cl]
2
*
Ph
OCO
2
Me
Ph
Ligand
12
or
13
Ar
10
11
O
THF
PN
R
1
R
2
NH
Ligand
Regioselectivity
Yield (%)
ee (%)
O
Ar
n
-Hexylamine
Morpholine
4-Me-C
6
H
4
NH
2
4-Me-C
6
H
4
NH
2
12
12
12
13
98:2
99:1
96:4
99:1
88
92
94
76
96 (
R
)
97
93
94
Ligand
12
: Ar = Ph
Ligand
13
: Ar = 1-Naph
ent-
12
O
ent-
12
R
1
R
2
NH
ent-
12
Cl
[Ir(COD)Cl]
2
Ir
Ir
P
ent-
12
O
H
2
C
N
Base-induced C-H activation
Ph
Ph
Scheme 5.4.
The regio- and enantioselective allylic substitution using chiral iridium complex has
been a subject of current interest [7]. The control of regio- and enantioselectivities in
allylic amination was mainly studied by Hartwig et al. [8] and Helmchen et al. [9],
respectively. Ohmura and Hartwig reported that the iridium complex of Feringa's phos-
phoramidate ligand (
R
a
,
R
,
R
) -
12
catalyzed the allylic amination of carbonate
10
to give
the branched product
11
with high enantioselectivities (Scheme 5.4) [8a]. An activated
form of the iridium complex was identifi ed by using ligand (
S
a
, S,
S
) -
ent
-
12
[8b] . The
activated complex was formed by
in situ
C-H activation at CH
3
group of a hindered
ligand
ent
-
12
. The use of this cyclometallation species led to improved activity, selectiv-
ity, and broader substrate scope for allylic amination. The reactions with aromatic
amines were also investigated [8c]. In these reactions, improvement in regioselectivity
and enantioselectivity was achieved by conducting reaction with the bulkier ligand
13
.
The direct Ir-catalyzed amination of allylic alcohols was also studied in the presence of
Lewis acid activators [8g]. The allylic amination in the presence of a catalytic amount
of triphenylboron (BPh
3
) as an activator occurred with high regioselectivities and high
enantioselectivities.
