Chemistry Reference
In-Depth Information
O
O
Ar
1.5 equiv Et
2
Zn
2% CuTC, 4%
16
CH
2
Cl
2
, -30
°
C to RT
1 or 10 equiv strene
O
X
Me
X
P N
Me
O
Ar
()
n
()
n
Et
16
n
= 1, X = Cl;
n
= 1, X = Br;
n
= 1, X = I;
n
= 0, X = Br;
n
= 2, X = Br
Up to 98%
ee
Ar = Ph or 2-naphthyl
Scheme 8A.10.
phosphoramidite ligand
17
. The desired products were obtained in good yields and up
to 94% ee ' s (Scheme 8A.11 ) [22] .
Me
Me
Me
Me
Et
2
Zn (1.2equiv)
Cu(O Tf)
2
(1 or 2 mol %)
THF, -78
OO
OO
O
Me
Me
C, 3 h
P N
°
O
O
O
O
3or6mol %
17
O
R
Et
R
17
R =
i
-Pr, C
6
H
11
,Ph,C
6
H
4
-
p
-OMe, C
6
H
4
-
p
-NMe
2
,C
6
H
4
-
p
-Cl, C
6
H
4
-
p
-Br,
C
6
H
4
-
p
-Me, C
6
H
4
CF
3
, 2-naphthyl, 2-furanyl, 2-thiophenyl
Scheme 8A.11.
Ph
Me
O
O
P N
O
O
Me
O
S
N
Me
O
S
N
Ph
NH
N
(10 mol %)
18
+
Me
2
Zn
Ar
1
Ar
2
CuTC (10 mol %)
Toluene, -20
Ar
1
Ar
2
C
°
70-80%
ee
Ar
1
=Ph,Ar
2
=Ph; Ar
1
=p-OMeC
6
H
4
,Ar
2
= Ph;
Ar
1
= p-ClC
6
H
4
,Ar
2
= Ph; Ar
1
= 2-Naph Ar
2
= Ph;
Ar
1
= Ph, Ar
2
= p-OMeC
6
H
4;
Ar
1
=Ph,Ar
2
= p-FC
6
H
4
;
Ar
1
= Ph, Ar
2
=2-Naph
Scheme 8A.12.
In 2005, Carretero et al. [23] described a catalyst system for the enantioselective
conjugate addition to α , β-unsaturated ketimines. The protocol was based on a copper-
catalyzed conjugate addition of dialkylzinc reagent to (2-pyridylsulfonyl)imines of chal-
cones in the presence of a chiral phosphoramidite ligand
18
. They proposed a mechanism
in which the metal-coordinating (2-pyridyl)sulfonyl moiety at the imino nitrogen and
the phosphoramidite ligand were the key elements for the high chemical yields and
enantioselectivities (Scheme 8A.12 ).
