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PCy
2
L
L
i
Pr
i
Pr
Pd
Pd
Cl
Cl
H
i
Pr
L=X-Phos
Scheme 9.38 Ligand control over syn elimination.
NH
t
Bu
[PdCl
2
(cod)] (5 mo l%)
X-Phos, LiCl, Cy
2
NMe
DMF-dioan e, 100°C, 24 h
+
OP(O )(OPh)
2
O
NH
t
Bu
O
91%
Scheme 9.39 Alkenylation without rearrangement, blocked by the XPhos ligand.
H
N
L
O
Pd
RPd(L)Cl
R
-Cl
-
O
O
N
N
R
H
N
Cl
RPd(L)Cl
H
+
/H
2
O
O
Pd
-L
L = (t-B u)
3
P
R
O
R
Scheme 9.40 Asymmetric induction by chiral pendant serving as ancillary ligand for
Pd.
olefins modified by chiral pendants capable of coordination to the Pd centre
(Scheme 9.40). The protocol developed was highly successful, affording high
yields of arylated and alkenylated ketones with high optical purity (90% and
more, Scheme 9.41). A broad preparative scope with consistently high yields
obtained with a wide range of aryl and vinyl chlorides and vinyl triflates
unambiguously reveals the key role of the (t-Bu)
3
P ancillary. The same
protocol without modification applies to aryl bromides.
156
A similarly high enantioselectivity with the same olefin was obtained with
aryl triflates in a system based on Ph
3
P ligand, with aryl bromides in a
system based on JohnPhos ligand and palladacycle precatalyst for aryl
bromides and with a ''phosphine-free'' system for aryl iodides, with media
and additives kept the same (Scheme 9.42).
157
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