Chemistry Reference
In-Depth Information
Sewald found that the CuI-catalyzed enantioselective addition of diethylzinc to
3-nitroacrolein dimethylacetal gave excellent enantioselectivity and yield [24]. Using
enantiomerically pure phosphoramidite ligands
19
and
20
(19: R
2
=H; 20: R
2
= CH
3
), up
to 98% ee was achieved (Scheme 8A.13).
R
1
O
2
N
OR
R
2
Zn, Cu
I
O
2
N
OR
*
R
2
R
2
19
OR
OR
<98% ee;
<94% yield
R
1
= Me, Et, Bu, (CH
2
)
6
CO
2
Me
O
O
O
O
P N
P
N
R
1
O
2
N
OR
R
2
Zn, Cu
I
R
2
R
2
O
2
N
OR
*
(M,S,S)
-19
(R
2
= H)
(P,S,S)
-20
(R
2
= CH
3
)
20
O
O
<98% ee;
<94% yield
R
1
=Me,Et,
i
Bu
Scheme 8A.13.
In 2007, Alexakis' group reported a novel class of chiral monodentate phosphorus
ligands, namely SimplePhos, which were easy to synthesize and were highly versatile in
application [25]. In the copper-catalyzed conjugate addition of diethylzinc to cyclohex-
2-enone, up to 95% ee was achieved (Scheme 8A.14).
O
O
CuTC (5 mol %)
21 (10 mol %)
+
2Et
2
Zn,
Et
2
O, -35
°
C, 15 h
Up to 95%
ee
R
3
R
1
R
1
=Ph,
p
-tolyl,
m
-CF
3
(C
6
H
4
); R
2
=Me,Et;
R
3
= Ph, 1-naphthyl, 2-naphthyl,
o
-MeO(C
6
H
4
)
R
2
R
2
PN
R
1
R
3
21 Simplephos
Scheme 8A.14.
Highly effective peptide-based ligands (e.g.,
22
-
25
) were successfully developed by
Hoveyda et al. (Scheme 8A.15). In 2002, these authors developed a highly effi cient and
enantioselective catalytic conjugate addition of dialkylzinc reagents to acyclic aliphatic
α
- unsaturated ketones using peptide - based ligands
24
[26]. This study outlined the
highly effi cient and enantioselective catalytic protocol for asymmetric conjugate addi-
tions of alkylmetals to acyclic aliphatic enones (Scheme 8A.16).
In 2003, an amino acid-based phosphane amide ligand
25
was shown to be effective
in Cu-catalyzed asymmetric conjugate addition reactions, giving products with up to
98% ee (Scheme 8A.17 ) [27] .
,
β
