Chemistry Reference
In-Depth Information
O
1)
127
,BEMP
CH
2
Cl
2
,-60
°
C
H
2
N
O
OH
CO
2
Et
N
+
OH
O
Ot-Bu
2) 6N-HCl
O
OH
93%, 97% ee
Scheme 8A.69.
R
128
(1 mol
%)
Cs
2
CO
3
O
Ph
N
+
OBu
t
CO
2
Bu
t
Ph
N
ch lorob enzen e
Ph
Ph
R
Up to 100% yield
Up to 75% ee
R=CO
2
Me, CONPh
2
,CN,SO
2
Ph
Scheme 8A.70.
The 1,4 - addition of
N
- (diphenylmethylene)glycine
tert
-butyl ester to vinyl ketones
was promoted by the chiral crown ether
129
, generating very good enantioselectivities
(up to 96% ee) with low catalyst loading (0.2 mol %) (Scheme 8A.71) [142].
O
129
(0.2 eq)
t
-BuOK
CH
2
Cl
2
,-78
°
C
O
Ph
N
Ph
N
CO
2
Et
OEt
COR
+
R
Ph
Ph
R=Me,Et
Up to 80% yield
Up to 96% ee
Scheme 8A.71.
Chiral guanidines such as
130
were applied in the conjugate addition of
N
-
(diphenylmethylene)glycine
tert
- butyl ester to vinyl ketones (Scheme 8A.72 ) [143] .
- Cyanoacetates
Taylor and Jacobsen demonstrated that chiral (salen)Al complex
131
was an effi cient
catalyst for the conjugate addition of α - aryl α-cyanoacetates to a wide range of α , β -
unsaturated imides [144]. They also investigated the use of
132
for the enantioselective
conjugate addition of α - cyanoacetates to acyclic α , β - unsaturated ketones [145] . This
methodology provided access to a wide range of useful chiral building blocks in high
yield and good ee (Scheme 8A.73).
8A.3.7. Conjugate Addition of
α
