Chemistry Reference
In-Depth Information
Ar
Ar
SO
2
Tol
O
N
O
O
O
OH
P
P
O
O
OH
N
Ar
Ar
SO
2
Tol
PA
3a
: Ar = Ph
PA
3b
: Ar = 4-CF
3
Ph
PA
4
O
O
Ph
O
OH
Ph
O
OH
P
P
Ph
Ph
O
O
VANOL
PA
5a
VAPOL
PA
5b
Figure 3.8.
Novel phosphoric acids.
O
O
PA
5b
(5-20 mol %)
Ether, rt
NH
2
R
R = sulfonyl or imide
N
O-
t-
Bu
HN
O-
t-
Bu
Ar
NHR
Ar
27 examples
80-99% yield
73-99% ee
R
2
R
2
EtO
2
C
CO
2
Et
PA
5b
(5 mol %)
Toluene, 50°C
HN
N
H
R
1
CO
2
Et
R
1
CO
2
Et
11 examples
85-98% yield
94-99% ee
Scheme 3.47.
lyst over phosphoric acids derived from BINOL (77% yield, 80% ee with PA
1j
vs. 99%
yield, 96% ee with PA
5b
) (Scheme 3.47 ).
Later, the utility of PAs
5a
and
5b
was extended to ring opening of
meso
- aziridines
[83]. This was the fi rst example of organocatalytic desymmetrization of
meso
- aziridines.
Introduction of more electron-withdrawing protecting groups on the nitrogen enhanced
both yields and enantioselectivities of products. Mechanical studies proposed that the
