1,9-dithia[2.2]paracyclophane: Synthesis, molecular structure, and properties

Full text of DOI:10.1021/jo951426c

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.
(1) Brown, C. J .; Fathing, A. C. Nature 1949, 164, 915.
(2) Fathing, A. C. J . Chem. Soc. 1953, 3621.
(3) Brown, C. G. J . Chem. Soc. 1953, 3265.
(4) Keehn, P. M.; Rosenfeld, S. M. Cyclophanes; Academic Press:
New York, 1983; Vols. 1 and 2.
(5) Vo¨gtle, F. Cyclophane Chemistry: Synthesis, Structures, and
Reactions; Wiley: England, 1993.
(6) Gorham, W. F. J . Polym. Sci., A-1 1966, 4, 3027.
(7) Chow, S. W.; Loeb, W. E.; White, C. E. J . Appl. Polym. Sci. 1969,
13, 2325.
(8) Itoh, T; Okuoka, S.; Kubo, M; Iwatsuki, S. J . Polym. Sci., Part-
A, Polym. Chem. 1995, 33, 359.
(9) Iwatsuki, S.; Kubo, M.; Yamashita, H. Chem. Lett. 1989, 729.
(10) Iwatsuki, S.; Kubo, M.; Kumeuchi, T. Chem. Lett. 1991, 1071.
(11) Itoh, T.; Iwasaki, T.; Kubo, M.: Iwatsuki, S. Polym. Bull. 1995,
35, 307.
(12) Sakurai, H.; Hoshi, S.; Kamiya, A.; Hosomi, A.; Kabuto, C.
Chem. Lett. 1986, 1781.
(16) Ostrowicki, A.; Vo¨gtle, F. Synthesis 1988, 1003.
(17) Vo¨gtle, F.; Mayenfels, P.; Luppertz, F. Synthesis 1984, 580.
(18) Illuminati, G.; Mandolini, L. Acc. Chem. Res. 1981, 14, 95.
(19) Knops, P.; Sendhoff, N.; Mekelburger, H. B.; Vo¨gtle, F. Top.
Curr. Chem. 1991, 161, 1.
(20) Blatt, A. H. Ed. Organic Syntheses; Wiley: New York, 1943;
Collect. Vol. 2, p 580.
(13) Sekiguchi, A.; Yatabe, T.; Kabuto, C.; Sakurai, H. J . Organomet.
Chem. 1990, 390, C27.
(14) Meurer, K.; Vo¨gtle, F.; Mannschreck, A.; Stu¨hler, G.; Puff, H.;
Roloff, A. J . Org. Chem. 1984, 49, 3484.
(21) March, J . Advanced Organic Chemistry: Reactions, Mecha-
nisms, and Structure, 3rd ed.; Wiley: New York, 1985; p 19.
(15) Meurer, K.; Luppertz, F.; Vo¨gtle, F. Chem. Ber. 1985, 118, 4433.
0022-3263/96/1961-1867$12.00/0 © 1996 American Chemical Society

1868 J . Org. Chem., Vol. 61, No. 5, 1996
Notes
Sch em e 1
Ta ble 2. Br id gin g Bon d Len gth s, In ter p la n a r Dista n ces,
a n d Str a in An gles of Cyclop h a n e 1 a n d
[2.2]P a r a cyclop h a n e
[2.2]paracyclophane4
cyclophane 1
a1 (Å)
a2 (Å)
b (Å)
p (Å)
1.774
1.497
1.860
2.883
3.134
a1 ) a2 (Å)
1.551
F igu r e 1. ORTEP drawing of the crystal structure of cyclo-
phane 1. The thermal ellipsoids are plotted at the 6.2%
probability level.
1.593
2.778
3.093
q (Å)
R1 (deg)
R2 (deg)
â1 (deg)
â2 (deg)
γ1 (deg)
γ2 (deg)
10.0
10.2
9.8
7.6
103.4
113.2
R1 ) R2 (deg)
â1 ) â2 (deg)
γ1 ) γ2 (deg)
12.6
Ta ble 1. Bon d Len gth s a n d An gles of Cyclop h a n e 1
11.2
113.7
than that of [2.2]paracyclophane (3.093 Å), but much less
than van der Waals contact distance (3.4 Å). The
increase in the distance is apparently a consequence of
the longer bond length between carbon and sulfur (1.860
Å) compared to that of a carbon-carbon bond (1.593 Å).
The electronic absorption spectra of cyclophane 1 and
p-(methylthio)toluene in THF are shown in Figure 2,
wherein cyclophane 1 shows a large amount of broaden-
ing compared to p-(methylthio)toluene, suggesting the
loss of ring planarity and a marked π-electron interaction
of both benzene rings as seen in the paracyclophane
series.22 The mass spectrum of cyclophane 1 shows peaks
at 244 (50%) assignable to the molecular ion peak of
cyclophane 1, 122 (100%), and 78 (12%). The peak at
122 is equal exactly to half the molecular weight of
cyclophane 1. Therefore, it is suggested that, when
cyclophane 1 is pyrolyzed in the vapor-phase, a reactive
intermediate p-thioquinonemethide is formed. Studies
of polymerizations of cyclophane 1 by vapor-phase py-
rolysis are now in progress.
Bond Lengths (Å)
S(1)-C(2)
C(2)-C(3)
C(3)-C(7)
C(5)-C(6)
C(6)-C(8)
1.774(4)
1.387(6)
1.385(6)
1.389(6)
1.497(8)
S(1)-C(8)
C(2)-C(4)
C(4)-C(5)
C(6)-C(7)
1.860(8)
1.387(6)
1.374(7)
1.381(7)
Bond Angles (deg)
C(2)-S(1)-C(8)
S(1)-C(2)-C(4)
C(2)-C(3)-C(7)
C(4)-C(5)-C(6)
C(5)-C(6)-C(8)
C(3)-C(7)-C(6)
103.4(3)
120.0(3)
119.8(4)
120.7(4)
120.2(5)
120.9(4)
S(1)-C(2)-C(3)
C(3)-C(2)-C(4)
C(2)-C(4)-C(5)
C(5)-C(6)-C(7)
C(7)-C(6)-C(8)
S(1)-C(8)-C(6)
120.8(3)
118.4(4)
120.4(4)
117.7(4)
121.6(5)
113.2(4)
out of the plane of the other four atoms (C(3), C(4), C(5),
and C(7)) toward the cyclophane cavity by 10.0° (R1) and
10.2° (R2), respectively, which is less than in the case of
[2.2]paracyclophane (12.6°). Also, the exocyclic bonds of
C-S and C-CH2 at the bridgehead carbon atoms of the
benzene rings are bent less (â1 ) 9.8° and â2 ) 7.6°) than
those in [2.2]paracyclophane (11.2°), indicating a smaller
degree of distortion of the benzene ring. The distance
between the two benzene rings (3.134 Å) is a little larger
Exp er im en ta l Section
Melting points are uncorrected. 1H- and 13C-NMR spectra
were recorded at 270 and 67.8 MHz in CDCl3 or DMSO-d6 with
TMS as an internal standard. EI mass spectra were recorded
at 70 eV.
(22) Ferguson, J . Chem. Rev. 1986, 86, 958.

Notes
J . Org. Chem., Vol. 61, No. 5, 1996 1869
100), 139 (25), 123 (22), 111 (39), 109 (18), 107 (51), 77 (67), 69
(15), 65 (15), 51 (15). Anal. Calcd for C7H8OS: C, 59.06; H,
5.76; S, 22.87; O, 11.41. Found: C, 59.12; H, 5.69; S, 22.90.
p-Mer ca p toben zyl Br om id e (6). Alcohol 5 (2.2 g, 15.7
mmol) was dissolved in 150 mL of ether. To the resulting
solution was added 50 mL of HBr, and the solution was stirred
for 20 h at rt. The organic layer was dried over anhydrous
MgSO4. The filtrate was evaporated under reduced pressure to
give a white solid, which was measured by gel permeation
chromatography (GPC) (standard polystyrenes, THF eluent) to
show many peaks, corresponding to the number average of
molecular weights of 200-2000. It was difficult to isolate
bromide 6 in a pure state because of its instability.
1,9-Dith ia [2.2]p a r a cyclop h a n e (1). Alcohol 5 (3.0 g, 21.7
mmol) was dissolved in 300 mL of ether. To the resulting
solution was added 90 mL of HBr, and the solution was stirred
for 20 h at rt. The water layer was extracted three times with
50 mL of ether, and the extracts were combined with the organic
layer and then dried over anhydrous MgSO4. The filtrate was
added dropwise to a refluxing mixture of 1700 mL of acetonitrile
and 4.41 g (21.7 mmol) of cesium hydroxide monohydrate over
a period of 20 h, and heating at reflux was continued for 33 h.
After cooling, the mixture was filtered to remove insoluble
materials, the solvent was evaporated in vacuo, and the residue
was dissolved in 300 mL of ethyl acetate. The resulting solution
was washed with H2O three times, dried over anhydrous MgSO4,
and concentrated to 20 mL under reduced pressure. The residue
was passed through a silica gel column using CHCl3 as eluent.
The first elution band portion was collected and concentrated
to give a residue, which was dissolved in a solution of benzene
and hexane (1:1 by volume). The resulting solution was passed
through a silica gel column using a solution of benzene and
hexane (1:1 by volume) as eluent, and the first and second
elution band portions were collected to give cyclophane 1 and
cyclic trimer 7 as white solids, respectively, which were recrys-
tallized from hexane to give colorless needles.
F igu r e 2. Electronic absorption spectra of 1 (s) and p-
(methylthio)toluene (- - -) in THF.
Bis(p-ca r boxyp h en yl) Disu lfid e (3). Diacid 3 was pre-
pared from p-aminobenzoic acid (2) and was recrystallized from
acetonitrile to give a pale yellow solid: yield 91%; mp 300 °C
dec; IR (KBr) 3200, 1653, 1560, 1397, 1271 cm-1 1H NMR
;
(DMSO-d6) δ 7.65 (d, J ) 8.4 Hz, 4H), 7.98 (d, J ) 8.4 Hz, 4H),
12.98-13.01 (br s, 2H). Anal. Calcd for C14H10O4S2: C, 54.88;
H, 3.30; O, 20.89; S, 20.93. Found: C, 55.24; H, 3.40, S, 20.86.
Cyclop h a n e 1: 80 mg (3.0%); mp 164-166 °C; 1H NMR
(CDCl3) δ 6.98 (d, J ) 7.0 Hz, 4H), 6.73 (d, J ) 7.0 Hz, 4H), 4.34
(s, 4H); 13C NMR (CDCl3) δ 131.1, 133.0, 140.6, 137.8, 42.4; MS
m/z (%) 244 (M+, 50), 122 (100), 78 (12). Anal. Calcd for
Bis(p-(m eth oxyca r bon yl)p h en yl) Disu lfid e (4). Diacid 3
(20.1 g, 65.4 mmol) was dissolved in 100 mL of thionyl chloride
and refluxed for 2 h. Excess thionyl chloride was distilled off to
give a yellow viscous oil, which was dissolved in 50 mL of ether,
and then the resulting solution was filtered to remove insoluble
material. The ether solution was added to a mixture of 100 mL
of Et3N and 200 mL of MeOH at reflux over 30 min and then
refluxed for 2 h. The reaction mixture was evaporated under
reduced pressure to give a brown solid, which was dissolved in
100 mL of CHCl3. The resulting solution was washed three
times with 100 mL of H2O, dried over anhydrous MgSO4,
concentrated to a 10-mL volume, and then passed through a
silica gel column using CHCl3 as eluent. The second elution
band portion was collected and dried under reduced pressure to
afford a brown solid, which was recrystallized from a solution
of benzene and hexane to give 20.3 g (93%) of 4 as pale brown
C
14H12S2: C, 68.80 H, 4.96; S, 26.24. Found: C, 68.68; H, 4.95;
S, 26.37.
Cyclic tr im er 7: 300 mg (11.5%); mp 152-153 °C; 1H NMR
(CDCl3) δ 6.94 (q, J ) 4.4 Hz, 12H), 4.00 (s, 6H); 13C NMR
(CDCl3) δ 127.0, 129.1, 130.9, 134.7, 37.3; MS m/z (%) 366 (M+,
100), 244 (55), 122 (82), 78 (14). Anal. Calcd for C21H18S3: C,
68.80; H, 4.96; S, 26.24. Found: C, 68.72; H, 4.98; S, 26.30.
X-r a y Str u ctu r e of 1.23 The crystal dimensions were 0.20
× 0.30 × 0.40 mm. Data collection was done at rt with graphite-
monochromatized copper KR radiation (λ ) 1.541 78 Å). Twenty
reflections were used for the unit cell determination, correspond-
ing to a monoclinic cell in the space group C2/c (No. 15) with
the following lattice parameters: a ) 12.560(2) Å, b ) 7.885(1)
Å, c ) 11.891(5) Å, R ) 90.00(0)°, â ) 99.70(1)°, γ ) 90.00(0)°,
V ) 1160.9(3) Å. For Z ) 4 and formula weight 244.40, the
calculated density was 1.40 g/cm3. A total of 1446 reflections
were measured in the range 3.0° < 2Θ < 130.0° by the 2Θ-ω
scan method with a scan rate of 12°/min; 968 reflections were
considered as observed. The structure was solved by the direct
methods and refined by full matrix least-squares refinement for
non-hydrogen atoms anisotropically. All hydrogen atoms were
located by the difference Fourier map and are included in the
refinement with isotropic temperature factors. The final R
factors were 0.0612 and Rw ) 0.0631.
needles: mp 103-105 °C; IR (KBr) 1680, 1561, 1408, 1264 cm-1
;
1H NMR (CDCl3) δ 7.97(d, J ) 7.4 Hz, 4H), 7.53 (d, J ) 7.4 Hz,
4H), 3.94 (s, 6H); MS m/z (%) 334 (M+, 66), 302 (100), 271 (100),
184 (80), 167 (15), 139 (26), 136 (28), 120 (32), 108 (17), 69 (30).
Anal. Calcd for C16H14O4S2: C, 57.46; H, 4.23; O, 19.14; S, 19.17.
Found: C, 57.51; H, 4.29; S, 19.23.
p-Mer ca p toben zyl Alcoh ol (5). To the suspension of 5.0 g
(132 mmol) of LiAlH4 in 300 mL of ether was added dropwise a
solution of 12.2 g (36.5 mmol) of 4 in 200 mL of THF at rt, and
then the solution was stirred for an additional 1 h. To the
reaction mixture was added slowly 100 mL of H2O, and then
the resulting solution was acidified by concentrated HCl. The
ether layer was washed with H2O and dried over anhydrous
MgSO4. The filtrate was evaporated under reduced pressure to
give a yellow oil, which was dissolved in CHCl3, and the resulting
solution was passed through a silica gel column using CHCl3 as
eluent. The yellow band portion was collected and dried under
reduced pressure to afford a pale yellow solid, which was
recrystallized from hexane to give 8.07 g (71%) of 5 as white
plates: mp 51-52 °C; IR (KBr) 3306, 2528, 1567, 1467, 1023
Ack n ow led gm en t. We express our thanks to Pro-
fessor Yoshiki Chujo, Kyoto University, for obtaining
mass spectra and to Professor Yukihiko Hashimoto,
Tokyo of University, for the X-ray analysis.
J O951426C
(23) The author has deposited atomic coordinates for this structure
with the Cambridge Crystallographic Data Centre. The coordinates
can be obtained, on request, from the Director, Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, UK.
1
cm-1; H NMR (CDCl3) δ 7.27 (d, J ) 6.8 Hz, 2H), 7.22 (d, J )
6.8 Hz, 2H), 4.64 (s, 2H), 3.45 (s, 1H), 1.70 (s, 1H); 13C NMR
(CDCl3) δ 129.6, 129.5, 127.8, 138.3, 64.8; MS m/z (%) 140 (M+,