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reaction conditions of the allylic alkylation were unsatisfactory. After considerable
variation of base and solvent, the conditions described in Scheme 8B.90 were found.
Dependence of selectivities follows the general characteristics described before, however,
enantioselectivities are slightly lower than with stabilized carbanions.
R
2
R
2
R
2
H
H
N
N
N
H
(2.0 equiv)
OCO
2
CH
3
R
1
R
1
R
1
[Ir(COD)Cl]
2
(2 mol %)
L59
(4 mol %)
Cs
2
CO
3
(1.0 equiv)
Dioxane, reflux, 3-8 h
b
l
R
1
=Ph R
2
=H
R
1
= 4-(MeO)C
6
H
4
,R
2
=H
R
1
= 4-(MeO)C
6
H
4
,R
2
=5-(MeO)
R
1
=Me,
b
/
l
= >97:3, 85% ee (49%)
b
/
l
= >97:3, 92% ee (82%)
b
/
l
= >97:3, 89% ee (85%)
b
/
l
= 93:7, 88% ee (43%)
b
/
l
= 87:13, 85% ee (55%)
R
2
=H
R
1
=
n
-Bu,
R
2
=H
Scheme 8B.90.
Ir-catalyzed allylic alkylations with indoles as nucleophiles.
8B.7.3.5. Allylic Substitutions with Aryl Zinc Compounds
On fi rst view, it appears
that organocopper compounds are the fi rst choice if allylic substitutions with nonstabi-
lized C-nucleophiles are concerned [328]. Scrutiny of the literature, however, shows that
alkyl
copper compounds yield branched, while
aryl
copper compounds yield mainly
linear alkylation products. For this reason, Alexakis et al. [329] investigated Ir-catalyzed
allylic substitutions with
aryl
zinc halides (Scheme 8B.91 ).
PhMgBr/ZnBr
2
/LiBr
1.5:0.75:1.5
Ph
+
R
OCO
2
Me
R
R
Ph
[Ir(COD)Cl]
2
/
L60
,
THF, rt
b
l
b
/
l
= 50:50, 93% ee (83%)
b
/
l
= 57:43, 95% ee (89%)
b
/
l
= 69:31, 74% ee (72%)
R=4-FC
6
H
4
,
R = 3,4-Cl
2
C
6
H
3
,
R=
c
-Hex,
Scheme 8B.91.
Allylic substitutions with a phenyl zinc reagent as pronucleophile.
Diphenylzinc was postulated as key intermediate of which both phenyl groups are
transferred. Regioselectivity was unsatisfactory; otherwise, the features typical for reac-
tions with stabilized carbanions, including absolute confi gurations of the products, were
observed.
As application, a formal synthesis of the antidepressant sertraline was carried out
(Scheme 8B.92 ).
