Chemistry Reference
In-Depth Information
Iminium catalysis
LUMO activation
Enamine catalysis
HOMO activation
SOMO catalysis
SOMO activation
O
R
H
O
Me
O
Me
O
Me
N
N
N
+2 e
-
-H
2
O
-1 e
-
O
Me
R
1
R
1
R
1
N
N
N
N
R
1
N
H
R
R
R
Figure 2A.3.
SOMO catalysis via single-electron oxidation of a transiently formed enamine.
SOMO-catalyzed
α
-allyation of aldehydes
O
Me
O
NBoc
N
20 mol % cat.*
O
NBoc
Catalyst =
(eq 1)
SiMe
3
H
H
t
-Bu
H
CAN, NaHCO
3
DME, -20°C
Ph
•TFA
70% yield
93% ee
SOMO-catalyzed
α
-vinylation of aldehydes
O
Me
O
N
20 mol % cat.*
O
Catalyst =
KF
3
B
Ph
(eq 2)
Ph
n
-Hex
H
H
t
-Bu
H
CAN, NaHCO
3
DME, H
2
O, -50°C
n
-Hex
Ph
•TFA
81% yield
94% ee
SOMO-catalyzed
α
-enolation of aldehydes
O
Me
O
OTBS
20 mol % cat.*
O
N
Catalyst =
(eq 3)
O
n
-Hex
H
t
-Bu
H
CAN, DTBP, -20°C
DME, H
2
O
H
O
n
-Hex
O
Ph
77% yield
92% ee
Scheme 2A.27.
SOMO - catalyzed enantioselective α - functionalization of aldehydes.
electron organocatalytic activation modes are accessible, but that they can also lead to
the development of a series of useful catalytic asymmetric transformations.
Recently, a conceptually novel one-electron asymmetric catalysis mode was brought
to fruition via the marriage of photoredox catalysis and organocatalysis. Photoredox
catalysis represents a powerful method of molecule activation that has found widespread
application in inorganic chemistry. One of the most studied photoredox catalysts is
Ru(bpy)
3
Cl
2
, which has found vast utility in several important fi elds of research (Fig.
2A.4) [43]. The combination of enamine and photoredox activation has led to the cre-
ation of a novel one-electron organocatalysis platform that is complementary to SOMO
activation.
As a fi rst example of the utility of this synergic catalysis concept, the enantioselective
intermolecular alkylation of aldehydes, a long-standing problem in asymmetric chemical
