Chemistry Reference
In-Depth Information
O
O
t
-Bu
t-
Bu
o
-Cl-C
6
H
4
CH
3
reflux, 27 h
-SO
2
-PhSOH
77%
S
t
-Bu
t
-Bu
O
+
S
Ph
S
S
t
-Bu
O
t
-Bu
O
O
Ph
Scheme 85
Synthesis of 1,2-di-
tert
-butylbenzene from 3,4-di-
tert
-butylthiophene 1,1-dioxide
with phenyl vinyl sulfone [
109
,
110
]
O
O
S
-SO
2
-
PhSO
2
H
92%
O
O
S
+
O
O
Ph
S
Ph
S
O
O
Scheme 86
Synthesis of
o
-di-(1-adamantyl)benzene via Diels-Alder cycloaddition of 3,4-di-
(1-adamantyl)thiophene 1,1-dioxide with phenyl vinyl sulfone [
59
]
O
O
O
F
toluene
110 °C, 20 h
Cl
F
F
Cl
F
+
+
S
-2 SO
2
,-2H
2
Cl
Cl
F
Cl
O
O
O
O
O
1 : 1, overall yield 86%
Scheme 87
Cycloaddition of 3-chloro-4-fluorothiophene 1,1-dioxide with 1,4-benzoquinone [
88
]
Category B
:
Benzene Ring-Forming Reactions by Removal of a Small Molecule
.
Cycloaddition of thiophene 1,1-dioxides with alkenic dienophiles often leads
directly to the formation of a benzene ring by expulsion of a small molecule such
as sulfur dioxide from the initial adducts. For example, 3,4-disubstituted thiophene
1,1-dioxides with bulky groups (Schemes
85
and
86
) react with alkenic dienophiles
such as phenyl vinyl sulfone followed by expulsion of a sulfur dioxide to afford the
corresponding highly congested benzene ring products in high yields, which are
difficult to prepare using other methods [
109
,
110
].
3,4-Disubstituted thiophene 1,1-dioxides react with 1,4-benzoquinone or
1,4-naphthoquinone through Diels-Alder reactions followed by the loss of sulfur
dioxide and oxidation, usually resulting in anthraquinone derivatives (Schemes
87
and
88
).
The reaction of tetrachlorothiophene 1,1-dioxide with a dienophile
87
affords
the primary product
88
in a stereospecific manner. In
88
, the cyclohexadiene ring
protons are placed in close proximity to the double bond of the other ring. Upon
dehalogenation of
88
with lithium/
tert
-butyl alcohol, the double bond is
regenerated to give
89
, accompanied by a stereospecific hydrogen atom transfer.
