Chemistry Reference
In-Depth Information
R
1
R
1
PA
1i
(5 mol %)
MS 5 A
Benzene, 6°C
CHO
NHR
3
H
2
NR
3
+
R
2
R
2
17 examples
49-96% yield
39-98% ee
R
3
R
3
R
3
O
N
N
HN
+H
2
NR
3
-H
2
O
R
1
R
1
R
1
R
1
H
H
H
H
R
2
R
2
R
2
R
2
Racemization
Reduction
R
1
NHR
3
R
2
Scheme 3.45.
O
R
2
HN
PA
1i
(10 mol %)
R
2
NH
2
(1.5 eq)
Hantzsch ester (2.2 eq)
MS 5A, cyclohexane, 50°C
12 examples
2:1 to 24:1
syn
selective
35-89% yield
82-96% ee
X
O
X
R
1
R
1
Enamine
catalysis
1,2-reduction
NHR
2
R
2
R
2
N
N
Aldol reaction
1,4-reduction
X
O
X
X
R
1
R
1
R
1
Scheme 3.46.
3.5.5. Novel Phosphoric Acids
Several novel phosphoric acids have been reported (Fig. 3.8).
TADDOL - based PAs
3a
and
3b
were synthesized and applied to the Mannich-type
reaction by the Akiyama group [78]. In addition, Terada et al. developed phosphorodi-
amidic acid PA
4
as a Brønsted acid for the direct Mannich reaction [79]. Antilla and
coworkers synthesized a novel phosphoric acid derivative PA
5a
or
5b
starting from
(
S
) - VANOL or (
S
)-VAPOL and demonstrated its catalytic activity in the addition of
nitrogen nucleophiles such as sulfonamides [80] and imides [81] to imines to produce
protected aminals. Furthermore, PA
5b
was found to be an excellent catalyst for the
reduction of α-imino esters with Hantzsch ester to provide highly enantioselective α -
amino esters [82] . Interestingly, VAPOL - based PA
5b
was proved to be a superior cata-
