Chemistry Reference
In-Depth Information
O
Et
2
AlCl
∗
+
O
Aux
CH
2
Cl
2
Aux
O
O
endo-
7
2
52a,b
endo:exo 98:2
dr (2R):(2S)
O
O
O
O
O
H
O
H
O
O
H
3
CO
52a
52b
-30 °C
-80 °C
86% dr 90:10
80% dr 99:1
Scheme 4.9
Diels-Alder reactions of dienophiles
52a,b
with cyclopentadiene (
2
).
Compared to carbohydrate acrylates, imine-dienophiles derived from carbohy-
drates have rarely been reported. The reason for this may be that the choice of
carbohydrate scaffolds containing amino groups is rather limited and formation
of acrylic esters is much more straightforward. Banks
et al
. have introduced car-
bohydrate acryloyl imines
53-55
(Scheme 4.10) [11]; interestingly, none of these
derivatives was prepared from natural nitrogen-containing carbohydrates. Instead,
d-galactose, d-fructose, and the diisopropylidene derivative of 2-keto-l-gulonic acid
O
R
1
= H
a
Et
2
AlCl, -20 to -78 °C
R
1
R
1
= Me
N
Aux
∗
b
+
c
R
1
= Ph
CH
2
Cl
2
Aux
N
O
O
O
R
1
= H
a
endo-
7
53-55
b
R
1
= Me
2
O
O
endo:exo >90:10
R
1
= Ph
c
dr (2R):(2S)
from D-galactose
from D-fructose
from 2-keto-L-gulonic acid
CH
3
CH
3
CH
3
CH
3
CH
3
H
3
C
O
O
O
O
O
O
O
O
O
O
O
O
O
O
H
3
C
N
O
H
3
C
O
O
O
N
O
O
N
H
3
C
CH
3
O
O
CH
3
O
CH
3
O
53
54
55
R
1
R
1
R
1
R
1
= H
R
1
= H
R
1
= H
a
a
a
83%
80%de
95%
87%de
74%
82%de
R
1
= Me
R
1
= Ph
R
1
= Me
b
98%
89%de
c
95%
endo:exo 4:1
63%de
b
89%
94%de
c
R
1
= Ph
99%
92%de
Scheme 4.10
Diels-Alder reactions of carbohydrate imine dienophiles
53-55
with cyclopenta-
diene (
2
).
Search WWH ::
Custom Search