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[172]. Enantioselective variants have been developed for Pd and more recently also for
Ir catalysts.
You et al. (Scheme 8B.88) [316] obtained good selectivities with a broad range of
arylallylic substrates, while regioselectivities with alkylallylic substrates were somewhat
lower. Improved results will probably be achieved with ligands other than
L59
. For once,
methylene chloride rather than THF was used as solvent. Concerning reaction mecha-
nism, it was determined by crossover experiments that reactions proceeded intermolecu-
larly. Furthermore, absolute confi gurations established for selected examples were as
expected on the basis of the general rule (cf. Section 8B.7.1.5.2).
O
O
O
O
[Ir(COD)Cl]
2
/
L59
/DBU
CH
2
Cl
2
,reflux
R
2
R
2
O
R
2
+
R
1
R
1
R
1
b
l
R
1
=Ar,
R
2
=Ar
b
/
l
= 98:2,
91-95% ee
(58-83%)
R
1
=Me,
R
2
=Ph
b
/
l
= 94:6,
90% ee
(61 %)
R
1
=
n
-C
5
H
11
,
2
=Ph
b
/
l
= 80:20, 89% ee
(52 %)
Scheme 8B.88.
Decarboxylative transformation of allyl
β
- keto esters.
8B.7.3.3. Enamines as Nucleophiles
Weix and Hartwig developed enamines as
nucleophiles. Considerable diffi culties had to be overcome to arrive at a useful proce-
dure (Scheme 8B.89) [326]. Note that a pure complex
ent
-
K3
(Ar = Ph,
L
=
ent
-
L59
,
Scheme 8B.77) in combination with [Ir(COD)Cl]2 was used as catalyst. Furthermore,
toluene was superior to THF as solvent. Only reactions with enamines derived from
methyl ketones were reported so far.
N
OCO
2
i
-Pr
O
O
R
2
+
R
1
R
1
R
2
R
1
R
2
ent-
K3
(Ar = Ph)/[Ir(COD)Cl]
2
ZnCl
2
(0.5 equiv)
Toluene, 25°C
l
b
R
1
= Ph, R
2
=
i-
Pr
b
/
l
= >99:1, 95% ee (86%)
R
1
= 2-furyl, R
2
=
i
-Bu
b
/
l
= 98:2, 97% ee (90%)
R
1
=
n
-Pr, R
2
=
i
-Bu
b
/
l
= 89:11, 83% ee (64%)
Scheme 8B.89.
Ir - catalyzed allylic substitutions with enamines.
8B.7.3.4. Reactions with Indoles
Indoles have been used successfully in Mo- and Pd-
catalyzed allylic substitutions. Their application in the Ir-catalyzed allylic substitution
was reported only recently by You et al. [327]. Initial results obtained under the standard
