Chemistry Reference
In-Depth Information
4-MeOC
6
H
4
C
6
H
4
-4-OMe
4-MeOC
6
H
4
C
6
H
4
-4-OMe
t
-BuOK
t
-BuOH, 60
o
C
75%
OO
MeO
2
C
CO
2
H
+
S
MeO
2
C
S
CO
2
Me
Scheme 42 A typical Hinsberg synthesis [
71
]
H
+
O
O
O
-
-
O
OMe
O
O
O
O
H
H
R
O
R
R
OMe
R
R
R
-MeO
-
S
MeO
2
C
S
MeO
2
C
S
MeO
2
C
R
OH
R
R
R
R
O
OH
CO
2
H
S
H
CO
2
H
O
MeO
2
C
-H
2
O
S
MeO
2
C
S
R
H
+
MeO
2
C
Scheme 43 The mechanism of the Hinsberg reaction
Me
Me
Me
Me
NaOMe, MeOH
94%
OO
NC
CONH
2
+
S
NC
S
CN
27
Scheme 44 A Hinsberg reaction using 2,2
0
-thiobis(acetonitrile) [
73
]
NaOMe
MeOH, reflux
47%
Ph
Ph
OO
+
S
O
O
PhOC
S
COPh
28
Scheme 45 A Hinsberg reaction with a non-aryl substituted 1,2-diketone [
74
]
One of the very few examples of the use of non-aryl substituted 1,2-diketones in
Hinsberg syntheses involved activation of the sulfur component with nitriles, rather
than esters (Scheme
44
). Thus, the reaction of butane-2,3-dione with 2,2
0
-thiobis
(acetonitrile) led to mononitrile-monoamide 27 [
73
].
Scheme
45
shows another, though untypical, 1,2-diketone with saturated sub-
stituents, used in the construction of a strained fused 2,5-dibenzoylthiophene
28 [
74
].
If diethyl oxalate is utilised as the 1,2-dicarbonyl component, with sodium
methoxide as base, a 3,4-dihydroxythiophene is generated as its disodium salt,
usually trapped by double
O
-alkylation, as indicated in Scheme
46
. Note that in
this situation, the product of the ring synthesis is the 2,5-diester [
75
,
76
], not an
ester-acid.
