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this reaction had opposite stereochemistry compared to the one obtained from the
reaction with the
-configured diene [33b]. The Diels-Alder products could be
cleaved from the carbohydrate scaffold either enzymatically or, more traditionally,
under acidic conditions.
In further studies the same authors made systematic modifications of the
hydroxy groups at C2 and C6 in
β
-configured glucose dienes [34]. The
results are similar to those obtained by Stoodley
et al
. [32] (vide supra) who con-
ducted their experiments independently.
Cyclic dienes attached to a carbohydrate scaffold are a rare occurrence. One
interesting example was reported by Bird and Lewis, who used cyclohexadienyl
ethers of isopropylidene glucose
147a,b
in the cycloaddition with naphthoquinone
(
148
) [35]. Acidic treatment of the Diels-Alder products induced a rearrangement
to the benzonaphthofuranones
150a,b
with concomitant loss of the carbohydrate
auxiliary. In this manner, excellent yields of the (
β
- and
α
+
)-isomers of
150a
and
150b
were
obtained (Scheme 4.22).
D-gluco
Aux
R
1
HO
H
3
C
H
3
C
O
O
R
1
O
O
H
∗
H
+
, H
2
O
∗
∗
O
O
O
+
∗
O
∗
O
-
Aux
H
∗
H
O
R
1
O
O
149
R
1
= H
O
CH
3
CH
3
R
1
= H
a
a
98% (+)-isomer
98% (+)-isomer
147
148
150
R
1
= CH
3
R
1
= CH
3
b
b
Scheme 4.22
Cycloadditions with carbohydrate-modified cyclic dienes
147
derived from
diisopropylidene glucose.
Hetero-Diels-Alder reactions with carbohydrate-bound dienes were among the
very first examples of the application of carbohydrate tools in stereoselective syn-
thesis. Pioneering work was performed by David
et al
. who reported examined
reactions of a diene derived from diisopropylidene glucose as early as 1974 [36].
Diene
153
was obtained in two steps from diisopropylidene glucose
93.
Interest-
ingly, in contrast to the carbohydrate dienes that were later extensively employed
by Stoodley and Lubineau,
153
is not an anomeric diene (Scheme 4.23).
D-gluco
H
2
/ Lindlar-cat
H
3
C
H
3
C
H
3
C
H
3
C
H
3
C
H
3
C
O
O
O
O
O
O
KOH, THF
petroleum ethe
r
HO
O
O
+
O
O
O
quant
96%
HO
OH
+ cis-isomer
151
O
O
O
93
O
CH
3
CH
3
O
CH
3
CH
3
O
CH
3
CH
3
152
153
trans/cis ca. 1:1
Scheme 4.23
Preparation of carbohydrate diene
153
from diisopropylidene glucose
93.
Cycloaddition
153
with of butyl glyoxylate gave a mixture of the diastereomeric
products
154a-d,
which could be separated into two fractions containing
154a
+
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