Chemistry Reference
In-Depth Information
reaction of aldimines, giving the corresponding
α
- amino
phosphonates
with
high
enantioselectivities.
More recently, Feng and others reported the hydrophosphonylation of aldehydes
201
using a chiral tridentate Schiff base aluminum complex (Scheme 5.61) [84]. The alumi-
num complex, formed
in situ
from tridentate Schiff base
203
and Et
2
AlCl, catalyzed the
asymmetric hydrophosphonylation with an extremely broad substrate scope, giving
chiral
- hydroxy phosphonates
202
in good yields with excellent enantioselectivities (up
to 97% ee.) [84a]. The strong positive nonlinear effect indicated that the reaction was
catalyzed by a dimeric aluminum species.
Shibasaki and others studied the catalytic enantioselective hydrophosphonylation of
aliphatic and cyclic imines by using various heterobimetallic complexes (Scheme 5.62)
[85]. The novel reaction of cyclic imine
204
with cyclic phosphate
205
was investigated.
The highest effi ciency of the reaction was achieved by using 2.5 mol % (
S
) - YbPB
207
,
α
Et
2
AlCl
O
O
OH
Schiff base
203
CH
2
Cl
2
/THF
OMe
P
+
R
H
H
OEt
RP
O
OMe
OEt
201
202
(Up to 97% ee)
R = Ar, 1-naphtyl, 2-naphtyl, alkyl
N
OH
t
-Bu
OH
Schiff base
203
Ad
Scheme 5.61.
O
O
N
(
S
)-YbPB
207
O
P
O
+
P
S
THF/toluene
O
H
O
NH
204
205
S
206
(99%, 99% ee)
K
O
O
O
O
O
Yb
O
K
K
(
S
)-YbPB
207
Scheme 5.62.
