Chemistry Reference
In-Depth Information
O
(NC)
2
HC
O
O
CH
2
(CN)
2
57
,(10mol%)
Toluene, rt
O
H
85-93% ee
77-99% yield
R
N
R
N
47
64
O
O
ArSH
57
,(10mol%)
63-85% ee
95-99% yield
CH
2
Cl
2
,4ÅMS,
Ar
(
)
( )
S
0~1
0~1
41
42
CH
2
(CN)
2
O
O
(NC)
2
HC
O
O
H
57
,(10mol%)
62-91% ee
28-95% yield
Ph
H
Ar
R'
H
Ar
To l u e n e , r t
65
66
Scheme 2B.12.
P(O)Ph
2
HN
63-76% ee
57-91% yield
PG
NO
2
57
(10 mol %)
N
Ar
68
+
RCH
2
NO
2
CH
2
Cl
2
NHBoc
H
Ar
75/25-97/3 dr
89-99% ee (major)
78-94% yield (major)
NO
2
PG = P(O)Ph
2
,
67
PG = Boc,
8A
R=H,
23A
R=alkyl,
23B
Ar
24
R
S
t
-Bu
H
N
N
H
N
H
R
N
O
n-
Pr
n-
Pr
69
(2 mol %)
CN
O
HO
84-98% ee
81-98% yield
HCN
+
To lu e n e , r t
R
1
R
2
R
1
R
2
70
71
Scheme 2B.13.
coworkers showed that
57
is an effective catalyst for conjugate additions of aryl thiols
to cyclic enones
41
and
- unsaturated imides
47
[42] (Scheme 2B.12 ), thereby further
expanding the scope of
57
with respect to asymmetric conjugate additions.
Takemoto and coworkers also explored
57
as a catalyst for an asymmetric aza-Henry
reaction, a 1,2-addition reaction of imines. In their initial report,
57
was found to afford
only moderate enantioselectivity for the addition of nitromethane (
23A
) to aromatic
N
- phosphinoylimines
67
(Scheme 2B.13) [43a]. In a more recent study, Takemoto and
coworkers discovered that the enantioselectivity of the aza-Henry reaction could be
dramatically improved with aromatic
N
- Boc imines
8A
[43b]. They also accomplished a
highly enantioselective and diastereoselective reaction between various nitroalkanes
α
,
β
