Chemistry Reference
In-Depth Information
OMe
Ti cat
(
L
m
/Ti/
L
n
)
O
O
TFA
+
(0.05 mol %)
RH
O
R
TMSO
L
5
/
Ti/
L
5
99.3% ee (>99%)
97.3% ee (>99%)
99.2% ee (>99%)
L
5
/
Ti/
L
6
99.4% ee (82%)
99.4% ee (>99%)
99.7% ee (>99%)
Aldehyde
Benzaldehyde
p
-Nitrobenzaldehyde
Furfural
Cl
Ph
Ph
OH
OH
OH
O
OH
OH
HO
CO
2
Me
OH
OH
OH
O
HO
CO
2
Me
Ph
Ph
Cl
L
1
L
2
L
3
L
4
L
5
Br
Br
Br
OH
OH
OH
OH
OH
OH
OH
OH
Br
Br
L
6
L
7
L
8
L
9
SPh
Br
Ph
Ph
OH
OH
OH
OH
OH
OH
OH
OH
SPh
Br
Ph
Ph
L
10
L
11
L
12
L
13
Scheme 8D.68.
Ding et al. applied the BINOL/diimine/Zn system [105] to the asymmetric HDA
reaction of benzaldehyde with Danishefsky's diene (Scheme 8D.69) [106]. A library of
chiral Zn catalysts is set up through the combination of a chiral diol library (12 members)
with those of a diimine library (20 members) in the presence of Et
2
Zn. The high through-
put screening of the resulting Zn catalyst library (240 members) shows that complex
42
is most effi cient to give >99% yield and 98% ee.
The chiral bis(oxazoline)-Cu(II) complexes also catalyze the HDA reactions of acyl
phosphonates and α-keto ester with enol ethers to afford cyclic enols with high
endo
-
selectivity (Scheme 8D.70). As in the carbonyl-ene reactions, the HDA reactions cata-
lyzed by the box-Cu(II) complexes (
18
) provide high chemical yield and enantioselectivity.
The absolute confi guration of the product is dependent on the oxazoline ring
substituent.
Evans and Jørgensen reported a variety of excellent and useful (H)DA reactions by
using chiral Cu(II) catalysts, such as box-Cu(II) complexes [107]. Due to space limita-
tions, we cannot describe the box-Cu(II) catalyses in detail.
