J . Org. Chem. 1996, 61, 1867-1869
1867
dithia[2.2]paracyclophane (1), 1,9-dioxa[2.2]paracyclo-
phane, and 1,9-diaza[2.2]paracyclophane have not yet
been synthesized. It is expected that the vapor-phase
pyrolysis of these heteroatom-bridged [2.2]paracyclo-
phanes would form very reactive p-quinonoid compounds
such as p-thioquinone methide, p-quinone methide, and
p-quinone methide imine in a pure state, which would
be polymerizable after the fashion of p-quinodimethane.
This paper describes the first successful synthesis of
a 1,9-dithia[2.2]paracyclophane (1), its properties, and its
molecular structure as determined by X-ray crystal-
lography. The synthesis is accomplished by the applica-
tion of both a cesium effect17,18 and a high dilution effect.19
1,9-Dith ia [2.2]p a r a cyclop h a n e: Syn th esis,
Molecu la r Str u ctu r e, a n d P r op er ties
Takahito Itoh,*,† Kenji Gotoh,† Noriyuki Ishikawa,†
Tosisige Hamaguchi,† and Masataka Kubo‡
Department of Chemistry for Materials,
Faculty of Engineering, Mie University, Kamihama-cho,
Tsu-shi, Mie 514, J apan and Instrumental Analysis Center,
Mie University, Kamihama-cho, Tsu-shi, Mie 514, J apan
Received August 2, 1995
In tr od u ction
Since the isolation of [2.2]paracyclophane from a
polymer mixture and its identification by X-ray analysis,1-3
many cyclophanes have been synthesized and their
chemical and physical properties have been extensively
studied.4,5 In the polymer field, it has long been recog-
nized that strained [2.2]paracyclophanes are useful
precursors of thin poly(arylene-ethylene) films which are
inert and transparent and have excellent barrier proper-
ties to nitrogen, oxygen, carbon dioxide, and hydrogen
gases and to moisture vapor. Strained [2.2]paracyclo-
phanes undergo vapor-phase pyrolysis under reduced
pressure at high temperature (600 °C) to give very
reactive p-quinodimethanes quantitatively which con-
dense on a cold surface below 30 °C and polymerize
spontaneously to give colorless transparent films free
from contamination and cross-linking.6,7 To date, [2.2]-
paracyclophane,6 1,1,2,2,9,9,10,10-octafluoro[2.2]para-
cyclophane,7 1,1,9,9-tetrafluoro[2.2]paracyclophane,8 1,9-
dichloro[2.2]paracyclophane,9 [2.2](2,5)thiophenophane,10
[2.2](2,5)pyridinophane,11 [2.2](2,5)pyrazinophane,11 and
N,N′-dimethyl[2.2](2,5)pyrrolophane11 have been studied
as precursors of p-quinodimethane-type monomers be-
cause they carry ethylene groups as bridges. In contrast
to the large number of ethylene-bridged [2.2]paracyclo-
phanes, there are few heteroatom-bridged [2.2]paracy-
clophanes except for 1,1,2,2,9,9,10,10-octamethyl-1,2,9,-
10-tetragerma[2.2]paracyclophane12 and 1,1,2,2,9,9,10,10-
oct a m et h yl-1,2,9,10-t et r a sila [2.2]pa r a cycloph a n e.13
Although heteroatom-bridged [2.2]metacyclophanes such
as 1,10-dithia[2.2]metacyclophane, 1-oxa-10-thia[2.2]-
metacyclophane, and 1-thia-10-aza[2.2]metacyclophane
have been successfully prepared by Vo¨gtle et al.,14-16
heteroatom-bridged [2.2]paracyclophanes such as 1,9-
Resu lts a n d Discu ssion
Cyclophane 1 was prepared successfully according to
Scheme 1.
Bis(p-carboxyphenyl) disulfide (3) was prepared in 91%
yield from p-aminobenzoic acid (2) in accordance with the
preparation of dithiosalicylic acid20 from anthranilic acid.
The diacid 3 was converted to bis(p-(methoxycarbonyl)-
phenyl) disulfide (4) in 93% yield by reaction with thionyl
chloride, followed by esterification with methanol. The
reduction of 4 with LiAlH4 in ether at room temperature
for 1 h gave a 71% yield of p-mercaptobenzyl alcohol (5),
which was subsequently treated with HBr at room
temperature to afford p-mercaptobenzyl bromide (6).
However, upon evaporation of the solvent, decomposition
of 6 took place to yield oligomeric materials. Owing to
the difficulty in isolating 6 in a pure state, 6 was used in
the subsequent reaction without isolation. A self-
coupling reaction of 6 in refluxing acetonitrile containing
cesium hydroxide under high dilution conditions afforded
cyclophane 1 in 3.0% yield and a cyclic trimer (7) in 12%
yield, together with a large amount of oligomer and
polymer. The cyclophane 1 could be sublimed at about
135 °C at a pressure of 0.1 mmHg.
In the 1H NMR spectrum of cyclophane 1, the aromatic
protons appear at 6.98 and 6.73 ppm as two split signals
in an AB pattern, shifted upfield by 0.18-0.35 ppm
relative to p-(methylthio)toluene (7.16 and 7.08 ppm).
This is ascribed to the anisotropic effect of one benzene
ring on the aromatic protons of the other ring and to the
rehybridization of the benzene carbon atoms due to ring
deformation. The molecular structure of cyclophane 1,
determined by X-ray crystallographic analysis, is shown
in Figure 1 and the intramolecular bond lengths and
angles are summarized in Table 1. The benzene rings
are bent into a boat shape, and the carbon-sulfur bond
lengths (S(1)-C(2) 1.774 Å and C(8)-S(1) 1.860 Å)
deviate slightly from the normal values (1.75 Å for sp2
carbon-sulfur and 1.81 Å for sp3 carbon-sulfur).21 The
bridging bond lengths, interplanar space distances, and
geometrical parameters (R1, R2, â1, â2, γ1, and γ2) of
cyclophane 1 are summarized in Table 2 together with
the corresponding values of [2.2]paracyclophane. The
C(2) and C(6) atoms of the benzene rings are displaced
† Department of Chemistry for Materials.
‡ Instrumental Analysis Center.
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0022-3263/96/1961-1867$12.00/0 © 1996 American Chemical Society