Chemistry Reference
In-Depth Information
Organocatalytic 1,4-reduction of
α,β
-unsaturated aldehydes
O
Me
EtO
2
C
CO
2
Et
20 mol % cat.*
N
R
1
O
R
1
O
Catalyst =
(eq 1)
H
t
-Bu
R
Me
H
Me
CHCl
3
, -30°C
R
•TFA
74-95% yield
90-97% ee
Organocatalytic 1,4-reduction of
α,β
-unsaturated ketones
O
Me
O
O
t
-BuO
2
C
CO
2
t
-Bu
20 mol % cat.*
N
Catalyst =
(eq 2)
H
Me
H
Me
Et
2
O, 0°C
n
n
Ph
O
R
R
•TCA
Me
66-89% yield
88-98% ee
Scheme 2A.8.
Reduction of
α
,
β
-unsaturated carbonyl compounds using iminium catalysis.
E
only
O
O
Me
Me
EtO
2
C
CO
2
Et
O
N
Me
H
t
-Bu
Me
H
Me
Me
O
•TCA
Same enantiomer (
S
)
Z
only
Scheme 2A.9.
Stereoconvergence of iminium - catalyzed hydride reduction.
2A.3. ENAMINE CATALYSIS
[1,9]
In the early 1970s, Hajos and Parrish reported the proline-catalyzed enantioselective
intramolecular aldol reaction in their approach toward the Wieland-Miescher ketone
(Scheme 2A.10 ) [19] .
O
O
O
3 mol % cat.*
Catalyst =
CO
2
H
N
H
DMF, RT
O
O
OH
100% yield
93% ee
Scheme 2A.10.
Hajos and Parrish ' s proline - catalyzed asymmetric aldol reaction.
