Chemistry Reference
In-Depth Information
cat.
(10 mol %)
CHO
CHO
O
tBuOOH (1.1 eq)
CF
3
Dioxane, 35°C
R
R
14 examples
Ar
F
3
C
60-84% yield
94:6 to >99:1 dr
84-96% ee
O
O
P
H
2
N
O
O
cat.
(10 mol %)
CHO
CHO
Ar
O
tBuOOH (1.1 eq)
F
3
C
TBME, 0°C
Ar = 2,4,6-(
i
-Pr)
3
C
6
H
2
R
R
R
R
CF
3
4 examples
75-95% yield
90-94% ee
cat.
Ar
H
2
O
Ar
N
tBuOOH
TRIP
CHO
H
R
R
Ar
Ar
N
PIRT
H
H
t-Bu
O
N
H
2
O
Ar
Ar
N
Product
TRIP
H
O
tBuOH
H
2
O
Scheme 3.54.
- unsaturated ketones with the
interesting fi nding that diamine salts had benefi cial effects on both reactivity and enan-
tioselectivity [93]. This is presumably because this catalyst may serve as a bifunctional
catalyst to possibly activate the enone substrate via iminium ion formation and hydrogen
peroxide via general base catalysis (Scheme 3.55).
Recently, the Toste group extended this novel concept to the asymmetric transition
metal catalysis [94]. Two different transformations, hydroamination and hydroalkoxyl-
ation of allenes, catalyzed by cationic gold(I) complexes generated products in excellent
yields with the use of chiral phosphate anion. Notably, they demonstrated that the chiral
counterion can be combined additively with chiral ligands to enable an asymmetric
transformation that cannot be achieved by either method alone (Scheme 3.56).
Rueping et al. reported a new dual catalysis procedure, where an enantioselective
activation of imines by a Brønsted acid is combined with a metal-catalyzed alkynylation
[95] . The
List et al. further extended this methodology to
α
,
β
-amino acids were obtained in good yields and with excellent enantioselectivi-
ties. They assumed that the reaction mechanism involves the formation of a chiral silver
α
