Chemistry Reference
In-Depth Information
Table 4.3
Diels-Alder reactions of enol ethers
95a,b
with heterodienes
96a-c.
Me
R
2
R
2
Me-O-tBu
Me
+
Aux
O
*
N
N
O
Aux
O
O
95
96
97-100
Entry
Dienophile
Heterodiene
Product
Yield
(%)
dr
Ph
Ph
Ph
+
N
N
Z : E
=
94 : 6
O
Aux
O
O
Aux
O
cis-
97
79 : 21
trans-
97
95 : 5
1
54
N
O
96a
cis-
97
+
trans-
97
(92 : 8)
H
3
C
H
3
C
O
O
O
CO
2
Et
CO
2
Et
O
CO
2
Et
+
N
N
O
Z : E
=
92 : 8
O
Aux
O
O
Aux
O
cis-
98
81 : 19
trans-
98
95 : 5
O
CH
3
CH
3
2
N
33
O
96b
cis-
98
trans-
98
(75 : 25)
+
(Z)
-
95a
+
(E)
-
95a
CF
3
CF
3
CF
3
+
N
N
Z : E
=
70 : 30
O
Aux
O
O
Aux
O
cis-
99
93 : 7
trans-
99
90 : 10
3
N
65
O
96c
cis-
99
trans-
99
(82 : 18)
+
H
3
C
H
3
C
O
O
Me
O
Ph
Ph
O
Me
4
N
60
88 : 12
N
O
O
Aux
O
O
O
CH
3
CH
3
FCb
96a
100
95b
(entries 1-3). The
(E)
-configured isomer of dienophile
95a
is more reactive than
its
(Z)
-counterpart; therefore, the cis/trans ratio of products
97
-
99
does not reflect
the
(Z/E)
ratio of the starting material. With dienes
96a
and
96b
the drs were
significantly higher for the
trans
-configured products (entries 1, 2), while similarly
high drs were obtained for both isomers of
99
(entry 3). Dienophile
95b
gave a dr
of 88 : 12 and 60% yield (entry 4).
Allenyl ether dienophile
95c
was reacted with dienes
96a
-
c,
and the resulting
products were subjected to basic isomerization, yielding
101
-
103
(Table 4.4).
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