Chemistry Reference
In-Depth Information
R
2
R
2
N
N
N
N
H
N
H
N
CF
3
F
3
C
H
H
R
1
R
1
S
S
CF
3
CF
3
N
N
CD-101
,R
1
=H,R
2
=CH=CH
2
CD-102
,R
1
=H,R
2
=CH
2
CH
3
Q-103
,R
1
=Me,R
2
=CH=CH
2
Q-104
,R
1
=Me,R
2
=CH
2
CH
3
CN-101
,R
1
=H,R
2
=CH=CH
2
CN-102
,R
1
=H,R
2
=CH
2
CH
3
QD-103
,R
1
=Me,R
2
=CH=CH
2
QD-104
,R
1
=Me,R
2
=CH
2
CH
3
O
O
PhSH
SPh
O
O
CD-101
,7%ee
CN-101
, -17% ee
101
, (10 mol %)
Ph
H
Ph
Ph
N
H
Ph
CH
2
Cl
2
,4ÅMS,
- 40°C
65
105
O
2
N
O
O
MeNO
2
103
, (10 mol %)
89-96% ee
80-94% yield
R
2
To lu en e, r t
95C
R
2
R
1
106
R
1
Ar
*
CH
2
(CO
2
Me)
2
NO
2
Ar
NO
2
MeOOC
COOMe
60A
61
Method A (Connon):
CN-101
, (10 mol %), CH
2
Cl
2
, -20°C, 75-99% ee, 63-94% yield.
Method B (Dixon):
Q-104
, (0.5 mol %), toluene, 0°C, 82-97% ee, 81-99% yield.
Scheme 2B.22.
coworkers reported the addition of thiophenol to
- unsaturated imide
65
with catalyst
101
, albeit in very low enantioselectivity [57]. In a paper published simultaneously by
Soos and coworkers, they showed that
103
mediated the 1,4-addition of nitromethane
to chalcone derivatives
95C
in high enantioselectivity [58]. Shortly thereafter, the
Connon and the Dixon groups independently reported highly enantioselective conjugate
additions of malonates to aromatic nitroalkenes
60A
catalyzed by
101
and
104
[59,60] .
These promising results in combination with the easy accessibility of the 9-thiourea
cinchona alkaloids
101 - 104
quickly attracted further investigations to extend the utility
of those catalysts in asymmetric conjugate additions. Some of the most important exam-
ples are highlighted in Scheme 2B.23 . Dixon [61] , Chen [62] , J ø rgensen [63] , and
Wennemers [64] expanded the scope of the nucleophiles for the
101 - 104
- catalyzed
conjugate additions to nitroalkenes. In the studies described by Dixon [61] and Chen
[62], respectively, new classes of carbon nucleophiles (
107
and
109
) were successfully
utilized in conjugate additions with nitroalkenes
60
. The effi cient additions of oxime
111
to nitroalkenes reported by Jørgensen provided a rare example of highly enantios-
elective organocatalytic conjugate additions with C-O bond formations [63]. The
α
,
β
