Synthetic Applications of 3,4-Bis(trimethylsilyl)thiophene: Unsymmetrically 3,4-Disubstituted Thiophenes and 3.4-Didehydrothiophene

Article abstract of DOI:10.1021/jo962191n

3,4-Bis(trimethylsilyl)thiophene (1a) was synthesized by three routes: (a) 1,3-dipolar cycloaddition; (b) modification of 3,4-dibromothiophene; and (c) intermolecular thiazole-alkyne Diels-Alder reaction. 3,4-Bis(trimethylsilyl)thiophene (1a) can function as a versatile building block for the construction of unsymmetrically 3,4-disubstituted thiophenes utilizing its step wise regiospecific mono-ipso-substitution followed by palladium-catalyzed cross-coupling reactions. In this manner, thiophenes 15, 16, 17a-j, 19a,b, 20, 22a-c, 23a,b, 24a-d, 25a-c, and 27a-j were prepared. The thiophene-3,4-diyl dimer 28 and thiophene-3,4-diyl tetramer 29 were also realized by palladium-catalyzed self-coupling reaction of organoboroxines. The stannylthiophene 31, formed by conversion of the C-Si bond to a C-Sn bond via boroxine 26c underwent both carbonylative coupling and lithiation followed by quenching with electrophiles to afford unsymmetrically 3,4-disubstituted thiophenes 33 and 36a-c as well. Moreover, 3,4-bis(trimethylsilyl)thiophene (1a) can be used as the starting material for the generation of the highly strained cyclic cumulene 3,4-didehy-drothiophene (2), whose existence was substantiated by its trapping reaction with several alkenes.

Full text of DOI:10.1021/jo962191n

1940
J . Org. Chem. 1997, 62, 1940-1954
Syn th etic Ap p lica tion s of 3,4-Bis(tr im eth ylsilyl)th iop h en e:
Un sym m etr ica lly 3,4-Disu bstitu ted Th iop h en es a n d
3,4-Did eh yd r oth iop h en e†,‡
Xin-Shan Ye§ and Henry N. C. Wong*
Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong
Received November 25, 1996X
3,4-Bis(trimethylsilyl)thiophene (1a ) was synthesized by three routes: (a) 1,3-dipolar cycloaddition;
(b) modification of 3,4-dibromothiophene; and (c) intermolecular thiazole-alkyne Diels-Alder
reaction. 3,4-Bis(trimethylsilyl)thiophene (1a ) can function as a versatile building block for the
construction of unsymmetrically 3,4-disubstituted thiophenes utilizing its stepwise regiospecific
mono-ipso-substitution followed by palladium-catalyzed cross-coupling reactions. In this manner,
thiophenes 15, 16, 17a -j, 19a ,b, 20, 22a -c, 23a ,b, 24a -d , 25a -c, and 27a -j were prepared.
The thiophene-3,4-diyl dimer 28 and thiophene-3,4-diyl tetramer 29 were also realized by palladium-
catalyzed self-coupling reaction of organoboroxines. The stannylthiophene 31, formed by conversion
of the C-Si bond to a C-Sn bond via boroxine 26c underwent both carbonylative coupling and
lithiation followed by quenching with electrophiles to afford unsymmetrically 3,4-disubstituted
thiophenes 33 and 36a -c as well. Moreover, 3,4-bis(trimethylsilyl)thiophene (1a ) can be used as
the starting material for the generation of the highly strained cyclic cumulene 3,4-didehy-
drothiophene (2), whose existence was substantiated by its trapping reaction with several alkenes.
In tr od u ction
arduous assignment. Although several approaches to
3,4-disubstituted thiophenes such as Hinsburg condensa-
tion,8 intramolecular reductive carbonyl coupling of
diketo sulfides,9 modification of 3,4-dibromothiophene,10
condensation of olefins with sulfur or sulfur dioxide,11 and
thermolysis of di-1-alkenyl disulfides,12 via (n-butylthio)-
methylene ketones13 and via R-oxoketene dithioacetals,14
Thiophenes occur abundantly as structural units in
many natural and non-natural molecules and enjoy
potential applications in flavor1 and pharmaceutical2
industries, in conducting polymer design,3 as well as in
nonlinear optical materials.4 Moreover, in the prepara-
tion of a wide range of cyclic and acyclic nonthiophene
molecules, thiophene derivatives are excellent synthetic
intermediates because of the unique electronic properties
of sulfur as well as the steric constraints of a five-
membered ring. For example, thiophenes can undergo
Diels-Alder reactions through their 1,1-dioxide deriva-
tives.5
Because of their synthetic importance, thiophenes have
been popular targets for synthetic chemists. Conse-
quently, the scope of the synthesis and applications of
thiophenes has broadened enormously in the past two
decades. However, the inclination of thiophene to endure
both metalation and electrophilic substitution preferen-
tially at R-positions6 has made the synthesis of 3-substi-
tuted7 and 3,4-disubstituted thiophenes an exceedingly
(6) Gronowitz, S. Adv. Heterocycl. Chem. 1963, 1, 1-124.
(7) Schulz, E.; Fahmi, K.; Lemaire, M. Acros Org. Acta 1995, 1, 10-
17. Kirsch, G.; Prim, D. Synth. Commun. 1994, 24, 1721-1726. Wu,
X.-M.; Chen, T.-A.; Zhu, L.-S.; Rieke, R. D. Tetrahedron Lett. 1994,
35, 3673-3674. Melamed, D.; Nuckols, C.; Fox, M. A. Tetrahedron Lett.
1994, 35, 8329-8332. Pearson, D. L.; Schumm, J . S.; Tour, J . M.
Macromolecules 1994, 27, 2348-2350. McCullough, R. D.; Lowe, R.
D.; J ayaraman, M.; Anderson, D. L. J . Org. Chem. 1993, 58, 904-
912. Fahmi, K.; Fache, F.; Lemaire, M. J . Mol. Catal. 1993, 80, 201-
208. Delabouglise, D.; Hmyene, M.; Horowitz, G.; Yassar, A.; Garnier,
F. Adv. Mater. 1992, 4, 107-116. Solooki, D.; Kennedy, V. O.; Tessier,
C. A.; Youngs, W. J . Synlett 1990, 427-428. Gronowitz, S.; Bobosik,
V.; Lawitz, K. Chem. Scripta 1984, 23, 120-122. Gronowitz, S.; Lawitz,
K. Chem. Scripta 1983, 22, 265-266. Wu, X.-M.; Rieke, R. D. J . Org.
Chem. 1995, 60, 6658-6659. Powell, P.; Sosabowski, M. H. J . Chem.
Res., Synop. 1995, 306-307. Sosabowski, M. H.; Powell, P. J . Chem.
Res., Synop. 1995, 402-403.
(8) Miyahara, Y. J . Heterocycl. Chem. 1979, 16, 1147-1151. Crom-
bie, D. A.; Kiely, J . R.; Ryan, C. J . J . Heterocycl. Chem. 1979, 16, 381-
382. Backer, H. J .; Stevens, W. Recl. Trav. Chim. Pays-Bas 1940, 59,
899-907. Garratt, P. J .; Vollhardt, K. P. C. J . Am. Chem. Soc. 1972,
94, 7087-7092.
† Dedicated to Professor Dr. Dieter Seebach on the occasion of his
60th birthday.
‡ Taken in part from the Ph.D. thesis of X.-S.Y., The Chinese
University of Hong Kong, 1996.
§ Present address: Department of Chemistry, The Scripps Research
Institute, La J olla, CA 92037.
(9) Nakayama, J . J . Synth. Org. Chem. J pn. 1994, 52, 308-317.
(10) (a) Gronowitz, S.; Moses, P.; Håkansson, R. Arkiv Kemi 1960,
16, 267. (b) Gronowitz, S.; Moses, P.; Ho¨rnfeldt, A.-B.; Håkansson, R.
Arkiv Kemi 1961, 17, 165-177. (c) Gronowitz, S.; Moses, P.; Ho¨rnfeldt,
A.-B. Arkiv Kemi 1961, 17, 237-247. (d) Gronowitz, S. Acta Chem.
Scand. 1961, 15, 1393-1395. (e) Gronowitz, S.; Moses, P. Acta Chem.
Scand. 1962, 16, 105-110. (f) Gronowitz, S.; Biezais, A.; Mathiasson,
B. Arkiv Kemi 1963, 21, 265-284. (g) Gronowitz, S.; Bugge, A. Acta
Chem. Scand. 1965, 19, 1271-1285. (h) Michael, U.; Gronowitz, S. Acta
Chem. Scand. 1968, 22, 1353-1355. (i) Christiansen, H.; Gronowitz,
S.; Rodmar, B.; Rodmar, S.; Rosen, U.; Sharma, M. K. Arkiv Kemi 1969,
30, 561-582. (j) Gronowitz, S.; Holm, B. Chem. Scripta 1972, 2, 245-
246. (k) Gronowitz, S.; Yom-Tov, B.; Michael, U. Acta Chem. Scand.
1973, 27, 2257-2270. (l) Spagnolo, P.; Zanirato, P.; Gronowitz, S. J .
Org. Chem. 1982, 47, 3177-3180. (m) Gronowitz, S.; Temciuc, M.;
Ho¨rnfeldt, A.-B. J . Heterocycl. Chem. 1993, 30, 1111-1116. (n) Tamao,
K.; Kodama, S.; Nakajima, I.; Kumada, M.; Minato, A.; Suzuki, K.
Tetrahedron 1982, 38, 3347-3354. (o) Brandsma, L.; Verkruijsse, H.
D. Synth. Commun. 1990, 20, 2275-2277. (p) Reddinger, J . L.;
Reynolds, J . R. J . Org. Chem. 1996, 61, 4833-4834. (q) Spagnolo, P.;
Zanirato, P. J . Chem. Soc., Perkin Trans. 1 1996, 963-964.
X Abstract published in Advance ACS Abstracts, March 1, 1997.
(1) Bertram, H.-J.; Emberger, R.; Gu¨ntert, M.; Sommer, H.; Werkhoff,
P. In Recent Developments in Flavor and Fragrance Chemistry; Hopp,
R., Mori, K., Eds.; VCH Verlagsgesellschaft mbH: Weinheim, 1993;
pp 241-259.
(2) Press, J . B. In The Chemistry of Heterocyclic Compounds:
Thiophene and Its Derivatives; Gronowitz, S., Ed.; J ohn Wiley & Sons,
Inc.: New York, 1991; Vol. 44, Part 4, pp 397-502.
(3) Bloor, D. Chem. Br. 1995, 31, 385-387. Roncali, J . Chem. Rev.
1992, 92, 711-738. Qian, R. Y. Makromol. Chem., Macromol. Symp.
1990, 33, 327-339. Bryce, M. R. Chem. Br. 1988, 24, 781-785. Cowan,
D. O.; Wlygul, F. M. Chem. Eng. News 1986, 64(29), 28-45.
(4) Nalwa, H. S. Adv. Mater. 1993, 5, 341-358. Fichou, D.; Garnier,
F.; Charra, F.; Kajzar, F.; Messier, J . In Organic Materials for Non-
linear Optics; Hann, R. A., Bloor, D., Eds.; Royal Society of Chemis-
try: London, 1989; pp 176-182.
(5) Press, J . B.; Russell, R. K. In Progress in Heterocyclic Chemistry;
Suschitzky, H., Scriven, E. F. V., Eds.; Pergamon Press: Oxford, 1992;
Vol. 4, pp 62-80.
S0022-3263(96)02191-3 CCC: $14.00 © 1997 American Chemical Society

Applications of 3,4-Bis(trimethylsilyl)thiophene
J . Org. Chem., Vol. 62, No. 7, 1997 1941
Sch em e 1
Sch em e 2
are available, they are generally not suitable for thio-
phenes with elaborate substituents. We report herein
full details of our strategy for synthesizing several
unsymmetrically 3,4-disubstituted thiophenes utilizing
3,4-bis(trimethylsilyl)thiophene (1a ) as a building block.
The use of 3,4-bis(trimethylsilyl)thiophene (1a ) as the
precursor for the generation of 3,4-didehydrothiophene
(2) is also described.
carbonyl ylide, namely thioformaldehyde S-methylide (3),
can be generated by two methods:21,22 one involved the
release of disiloxane from bis(trimethylsilylmethyl) sul-
foxide (4) through a pathway related to the sila-Pum-
merer rearrangement,23 the other involved the 1,3-
elimination of chloromethyl (trimethylsilyl)methyl sulfide
(5) catalyzed by cesium fluoride in acetonitrile at room
temperature (Scheme 2).
The thiocarbonyl ylide 3 is able to undergo cycloaddi-
tions with conjugated dipolarophiles to lead to di- or
tetrahydrothiophenes. In considering the fluoride-
induced desilylation, we chose the former strategy to
accomplish the synthesis of the silylated thiophene 1a
using bis(trimethylsilyl)acetylene as a dipolarophile. Our
synthetic approach was shown below (Scheme 3).
Resu lts a n d Discu ssion
(a ) Syn th esis of 3,4-Bis(tr im eth ylsilyl)th iop h en e
(1a ). Recently, the successful conversions of 3,4-bis-
(trimethylsilyl)furan to 3,4-disubstituted furans, involv-
ing the concomitant functions of silyl groups as protecting
groups15 and as ipso-substitution directors,16 have been
achieved.17 Encouraged by these results, we are inter-
ested in synthesizing 3,4-bis(trimethylsilyl)thiophene (1a )
in which both the C-3 and C-4 trimethylsilyl groups can
be modified and manipulated for later synthetic applica-
tions. Possessing a strong directing effect, the trimeth-
ylsilyl groups of 1a should be easily replaced by other
groups, preferably in a stepwise manner (Scheme 1).
The first synthesis of 3,4-bis(trimethylsilyl)thiophene
(1a ) was reported by Shepherd,18 who employed sequen-
tial low-temperature lithiations followed by silylations
starting from 3,4-dibromothiophene.19 The first lithiation
was performed with n-butyllithium, and the second
lithiation step involved treatment of 3-bromo-4-(trimeth-
ylsilyl)thiophene with 2 equiv of tert-butyllithium.
We independently explored the synthesis of 1a via
three routes: (1) 1,3-dipolar cycloaddition, (2) silylation
utilizing an ultrasonic technique, and (3) intermolecular
thiazole-alkyne Diels-Alder reaction.
Sch em e 3
(1) 1,3-Dip ola r Cycloa d d ition . Thiocarbonyl ylides20
are useful reactive intermediates for the synthesis of
heterocycles containing a sulfur atom. The parent thio-
Bis[(trimethylsilyl)methyl] sulfide (8),24 readily pre-
pared by the reaction of (chloromethyl)trimethylsilane (7)
with sodium sulfide in water at reflux in the presence of
phase-transfer catalyst tetrabutylammonium iodide, was
oxidized by sodium periodate25 at lower temperature (-10
to 0 °C) to give the sulfoxide 4. Treatment of 4 with bis-
(trimethylsilyl)acetylene at 100 °C in HMPA gave the 1,3-
dipolar cycloadduct 9, which was treated with DDQ26 in
chloroform at 65 °C to produce 3,4-bis(trimethylsilyl)-
thiophene (1a ).
(11) Voronkov, M. G.; Udre, V.; Taube, A. Khim. Geterotsikl. Soedin.
1971, 7(6), 755-758; Chem. Abstr. 1972, 76, 25004m. Yur’ev, Yu.K.;
Khmel’nitskii, L. I. Dokl. Akad. Nauk SSSR 1953, 92, 101-104; Chem.
Abstr. 1954, 48, 10725i.
(12) Boelens, H.; Brandsma, L. Recl. Trav. Chim. Pays-Bas 1972,
91, 141-145.
(13) Rasmussen, C. A. H.; de Groot, A. Synthesis 1983, 575-576.
(14) Thomas, A.; Singh, G.; Ila, H.; J unjappa, H. Tetrahedron Lett.
1989, 30, 3093-3096. Bhat, L.; Thomas, A.; Ila, H.; J unjappa, H.
Tetrahedron 1992, 48, 10377-10388.
(15) Chan, T. H.; Fleming, I. Synthesis 1979, 761-786.
(16) Benkeser, R. A.; Hoke, D. I.; Hickner, R. A. J . Am. Chem. Soc.
1958, 80, 5294-5297. Dean, F. B.; Eaborn, C.; Webster, D. E. J . Chem.
Soc. 1959, 3031-3035. Sakurai, H. Pure Appl. Chem. 1987, 59, 1637-
1646. Ushakov, S. N.; Itenberg, A. M. Zh. Obshch. Khim. 1937, 7,
2495-2498; Chem. Abstr. 1938, 32, 20838. Lambert, J . B. Tetrahedron
1990, 46, 2677-2689. White, J . M. Aust. J . Chem. 1995, 48, 1227-
1251.
(17) (a) Ho, M. S.; Wong, H. N. C. J . Chem. Soc., Chem. Commun.
1989, 1238-1240. (b) Song, Z. Z.; Zhou, Z. Y.; Mak, T. C. W.; Wong,
H. N. C. Angew. Chem., Int. Ed. Engl. 1993, 32, 432-434. (c) Song, Z.
Z.; Wong, H. N. C. Liebigs Ann. Chem. 1994, 29-34. (d) Song, Z. Z.;
Wong, H. N. C. J . Org. Chem. 1994, 59, 33-41. (e) Song, Z. Z.; Ho, M.
S.; Wong, H. N. C. J . Org. Chem. 1994, 59, 3917-3926. (f) Song, Z. Z.;
Wong, H. N. C. J . Chin. Chem. Soc. (Taipei) 1995, 42, 673-679.
(18) O’Donovan, A. R. M.; Shepherd, M. K. Tetrahedron Lett. 1994,
35, 4425-4428.
(19) Gronowitz, S. Acta Chem. Scand. 1959, 13, 1045-1046.
(20) Kellogg, R. M. Tetrahedron 1976, 32, 2165-2184. Yamano, T.;
Tanaka, M.; Takanohashi, K. Heterocycles 1993, 36, 2397-2405. Ikeda,
M.; Tamura, Y.; Yamagishi, M.; Goto, Y.; Niiya, T.; Sumoto, K.
Heterocycles 1984, 22, 981-985. Huisgen, R.; Li, X.-Y. Heterocycles
Although the synthesis of the building block 1a was
successfully realized by this route, the yield of the key
1983, 20, 2363-2368. Terao, Y.; Aono, M.; Takahashi, I.; Achiwa, K.
Chem. Lett. 1986, 2089-2092. Terao, Y.; Tanaka, M.; Imai, N.; Achiwa,
K. Tetrahedron Lett. 1985, 26, 3011-3014. Aono, M.; Terao, Y.; Achiwa,
K. Heterocycles 1986, 24, 313-315.
(21) Aono, M.; Hyodo, C.; Terao, Y.; Achiwa, K. Tetrahedron Lett.
1986, 27, 4039-4042. Morimoto, Y.; Achiwa, K. Chem. Pharm. Bull.
1987, 35, 3845-3849. Aono, M.; Terao, Y.; Achiwa, K. Heterocycles
1995, 40, 249-260.
(22) Hosomi, A.; Matsuyama, Y.; Sakurai, H. J . Chem. Soc., Chem.
Commun. 1986, 1073-1074. Hosomi, A.; Hayashi, S.; Hoashi, K.;
Kohra, S.; Tominaga, Y. J . Chem. Soc., Chem. Commun. 1987, 1442-
1443.
(23) Brook, A. G.; Anderson, D. G. Can. J . Chem. 1968, 46, 2115-
2118.
(24) (a) Terao, Y.; Aono, M.; Imai, N.; Achiwa, K. Chem. Pharm. Bull.
1987, 35, 1734-1740. (b) Hosomi, A.; Ogata, K.; Ohkuma, M.; Hojo,
M. Synlett 1991, 557-558.
(25) Russel, G. A.; Ochrymowycz, L. A. J . Org. Chem. 1970, 35,
2106-2108.
(26) Mattocks, A. R. J . Chem. Soc., Perkin Trans. 1 1978, 896-905.

1942 J . Org. Chem., Vol. 62, No. 7, 1997
Ye and Wong
Sch em e 4
Sch em e 5a
1,3-dipolar cycloaddition step is low, i.e., 10% from sulfide
8. All efforts to improve the yield were unfruitful. For
example, change of the reaction temperature only led to
inferior yields. This unsatisfactory outcome may result
from the low reactivity of the dipolarophile bis(trimeth-
ylsilyl)acetylene, which carries bulky trimethylsilyl groups,
thus making the formation of the sila-Pummerer rear-
rangement product a major pathway.
a
Reagents and conditions: (i) sealed tube, 340-360 °C, Et3N
or DBU; (ii) sealed tube, 325-340 °C, DBU.
assembled via a crucial intramolecular thiazole-alkyne
cycloaddition.33 The intermolecular version of these
reactions had hitherto been unexplored. After a great
deal of experimentation, however, it was eventually found
that at the temperature range of 320-360 °C alkynes 13
were able to react with 4-methylthiazole (12a )34a or
4-phenylthiazole (12b),34b with the latter being much
more competent in terms of yields, providing 3-substi-
tuted or 3,4-disubstituted thiophenes 1 after extrusion
of acetonitrile or benzonitrile (Scheme 5). In this way,
3,4-bis(trimethylsilyl)thiophene (1a ) was obtained in an
inferior yield by reacting 12a with bis(trimethylsilyl)-
acetylene (13a ) in Et3N at 360 °C or in 92% yield from a
similar reaction between 12b and 13a in DBU at 325 °C.
Noteworthy is that thiazole 12b constantly gave much
better yields of 1. We still lack an explanation for this
observation, but it is likely due to the detrimental
pressure effect in the sealed tube caused by the lower-
boiling acetonitrile formed in the cycloreversion. The
thermal reaction between 12b and 13a is quite amenable
to a large-scale production of 1a , which was generated
routinely in about an 8 g quantity in one single run (see
Experimental Section). A base was somehow needed to
play the role as a proton scavenger because 1a can
undergo a facile acid-catalyzed rearrangement.35 Higher
temperatures and longer reaction times made the rear-
rangement to occur more easily. Reaction of thiazole 12a
and acetylene 13b in DBU at 340 °C again only gave 1b
in unsatisfactory yield. Nevertheless, 12b reacted with
13c and 13d in the presence of DBU to produce in good
yields 1c and 1d , respectively. The preparation of 1e
from 12b and 13e, on the other hand, did not require a
base. It is noteworthy that the aforementioned reactions
did not occur when the temperatures were lower than
300 °C.
To overcome the yield limitation, new pathways were
therefore required.
(2) Mod ifica tion of 3,4-Dibr om oth iop h en e. Sily-
lation of halothiophenes is a common access to silylth-
iophenes. Several methods leading to silylated thiophenes
have been established, which involved organolithium,18,27
organosodium,28 and organomagnesium27a,29 routes. Very
recently, an electrochemical pathway was also reported.30
Among the numerous approaches, we were especially
interested in the synthesis of 3-(trimethylsilyl)thiophene
through the reaction between 3-bromothiophene with
chlorotrimethylsilane and magnesium in THF under
ultrasonication due to its simplicity and convenience.29b
This prompted us to study the possibility of synthesizing
3,4-bis(trimethylsilyl)thiophene (1a ) employing the sono-
chemical cross-coupling of 3,4-dibromothiophene (11)
with Me3SiCl (Scheme 4).
3,4-Dibromothiophene (11) was easily obtained by
bromination31 of thiophene followed by selective dehalo-
genation19 with Zn-dust in acetic acid. No reaction took
place when a mixture of 11, Me3SiCl, and magnesium
turnings (molar ratio 11:Me3SiCl:Mg ) 1:2.25:2.25) in
THF in a sealed tube was kept under ultrasonication
(output power 35 W) even for 4 days. While magnesium
powder was used instead of magnesium turnings under
the same conditions, surprisingly, the reaction occurred
slowly and was complete in about 7 days. The yield is,
however, modest, usually only 30%. This seems to arise
also from the steric effect of two bulky â-substituents in
thiophene rings. It should be noted that a stronger
ultrasonic irradiation source (Branson SONIFIER 450)
did not seem to initiate the reaction and, therefore,
resulted in the recovery of the starting material 11.
(3) In ter m olecu la r Diels-Ald er Cycloa d d ition -
Cyclor ever sion . Owing to the low reactivity of thia-
zoles toward Diels-Alder cycloaddition,32 only a few
examples are known in which thiophene rings were
(b) P r ep a r a tion of Un sym m etr ica lly 3,4-Disu b-
stitu ted Th iop h en es. The use of the trimethylsilyl
group to assist in the iodination of aromatic species has
been well-documented. For example, a method of iodi-
nating aryltrimethylsilanes using iodine or iodine mono-
chloride and a silver salt to activate the electrophile was
reported by J acob.36 This mild method was also used to
(27) (a) Deans, F. B.; Eaborn, C. J . Chem. Soc. 1959, 2303-2304.
(b) Haiduc, I.; Gilman, H. Rev. Roum. Chim. 1971, 16, 305-310; Chem.
Abstr. 1971, 75, 36230n. (c) Fro¨hlich, H.; Kalt, W. J . Org. Chem. 1990,
55, 2993-2995. (d) Tour, J . M.; Wu, R. Macromolecules 1992, 25, 1901-
1907. Tour, J . M.; Wu, R.; Schumm, J . S. J . Am. Chem. Soc. 1991,
113, 7064-7066.
(28) Effenberger, F.; Ha¨bich, D. Liebigs Ann. Chem. 1979, 842-857.
(29) (a) Benkeser, R. A.; Torkelson, A. J . Am. Chem. Soc. 1954, 76,
1252-1253. (b) Goldberg, Yu.; Sturkovich, R.; Lukevics, E. Synth.
Commun. 1993, 23, 1235-1238.
(33) J acobi, P. A.; Weiss, K. T.; Egbertson, M. Heterocycles 1984,
22, 281-286. J acobi, P. A.; Egbertson, M.; Frechette, R. F.; Miao, C.
K.; Weiss, K. T. Tetrahedron 1988, 44, 3327-3338.
(34) (a) Commercially available. (b) Erlenmeyer, H.; Becker, C.;
Sorkin, E.; Bloch, H.; Suter, E. Helv. Chim. Acta 1947, 30, 2058-2062.
(35) Seyferth, D.; White, D. L. J . Am. Chem. Soc. 1972, 94, 3132-
3138.
(30) Deffieux, D.; Bonafoux, D.; Bordeau, M.; Biran, C.; Dunogue`s,
J . Organometallics 1996, 15, 2041-2046.
(31) Steinkopf, W.; J acob, H.; Penz, H. Liebigs Ann. Chem. 1934,
512, 136-164.
(32) Thiazole and Its Derivatives; Metzger, J . V., Ed.; J ohn Wiley &
Sons, Inc.: New York, 1979.
(36) J acob, L. A.; Chen, B.-L.; Stec, D. Synthesis 1993, 611-614.
Wilson, S. R.; J acob, L. A. J . Org. Chem. 1986, 51, 4833-4836.

Applications of 3,4-Bis(trimethylsilyl)thiophene
J . Org. Chem., Vol. 62, No. 7, 1997 1943
Ta ble 1. Son oga sh ir a Cou p lin g Rea ction of 14 w ith
Ter m in a l Alk yn es
Sch em e 6
convert silylated furans to their corresponding iodinated
products in our laboratory.17c Such practice was also
applied to thiophene 1a . A regiospecific mono-ipso-
iodination cleanly converted 1a into iodide 14, when 1a
was treated with iodine and silver trifluoroacetate in
THF at -78 °C (Scheme 6). To avoid the formation of
the side product diiodide, it is necessary to maintain the
reaction temperature at -78 °C.
With the aim to test the versatility of our strategy for
the synthesis of 3,4-disubstituted thiophenes, the cou-
pling reaction37 of 3-iodo-4-(trimethylsilyl)thiophene (14)
with organostannanes was examined. It was found that
14 underwent a smooth cross-coupling reaction with
ethynyltributyltin to give 3-ethynyl-4-(trimethylsilyl)-
thiophene (15) in 90% yield. The reaction made use of
tetrakis(triphenylphosphine)palladium(0) as catalyst and
dioxane as solvent. Under similar conditions, reaction
of 14 with bis(tributylstannyl)acetylene provided alkyne
16 (Scheme 6). It should be noted that the trimethylsilyl
group of 16 is very acid sensitive due to the strong
rearrangement tendency;35 for this reason, it is necessary
to add triethylamine to the reaction solvent and the
chromatography eluent in order to secure pure 16.
3-Iodo-4-(trimethylsilyl)thiophene (14) was also trans-
formed to 17 by the Sonogashira coupling reaction38 with
various terminal alkynes. The results are summarized
in Table 1. This is a convenient route for the synthesis
of 3-alkynyl-4-(trimethylsilyl)thiophenes. All these reac-
tions were performed under the same conditions: iodide
14 (1 equiv), alkynes (1.5 equiv), Pd(PPh3)4 (0.1 equiv),
CuI (0.2 equiv), Et3N-MeCN (v/v 2.5:1) as mixed solvent,
reflux temperature. The yields are usually high.
The remaining trimethylsilyl group of 17c was replaced
by iodine in merely 30% yield under more rigorous
conditions,16c,37 presumably due to alkyne interference.
All attempts to improve the yield such as changing
solvents or anions of the silver salts, and using iodine
monochloride instead of iodine, were unfruitful. Further
Sonogashira reaction38 of the resulting iodide 18 gave 3,4-
dialkynylthiophenes 19 in much better yields (Scheme
7).
Sch em e 7
Sch em e 8
initially converted to 20 by Suzuki coupling reaction.39
Thus, 14 coupled with phenylboronic acid in the presence
of Pd(PPh3)4 catalyst and 2 M Na2CO3 in methanol-
toluene to give 20 in 77% yield. Subsequent regiospecific
iodination of 20 produced another key intermediate 21
in 67% yield (Scheme 8).
3-Iodo-4-phenylthiophene (21) underwent a smooth
Heck-type cross-coupling reaction40 with terminal alkenes
to lead to alkenyl-substituted thiophenes 22. The reac-
tions were carried out either under typical Heck condi-
tions or under phase-transfer41 conditions. All coupling
To widen the scope of our strategy, iodide 14 was
(37) Stille, J . K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508-524.
(38) (a) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett.
1975, 4467-4470. (b) Cassar, L. J . Organomet. Chem. 1975, 93, 253-
257. (c) Alvarez, A.; Guzma´n, A.; Ruiz, A.; Velarde, E.; Muchowski, J .
M. J . Org. Chem. 1992, 57, 1653-1656. (c) Rossi, R.; Carpita, A.;
Bellina, F. Org. Prep. Proced. Int. 1995, 27, 129-160. (d) Furstner,
A.; Seidel, G. Tetrahedron 1995, 51, 11165-11176.
(39) Miyaura, N.; Yanagi, T.; Suzuki, A. Synth. Commun. 1981, 11,
513-519. Martin, A. R.; Yang, Y.-H. Acta Chem. Scand. 1993, 47, 221-
230. Suzuki, A. Pure Appl. Chem. 1991, 63, 419-422. Miyaura, N.;
Suzuki, A. Chem. Rev. 1995, 95, 2457-2483. Kubiak, G. G.; Confalone,
P. N. Tetrahedron Lett. 1990, 31, 3845-3848. Miyaura, N.; Yamada,
K.; Suginome, H.; Suzuki, A. J . Am. Chem. Soc. 1985, 107, 972-980.

1944 J . Org. Chem., Vol. 62, No. 7, 1997
Ye and Wong
Sch em e 9a
Ta ble 2. Su zu k i Cou p lin g Rea ction of 21 w ith
Ar en ebor on ic Acid s
a
Reagents and conditions: for 22a and 22b , Pd(OAc)2, Et-
COCHdCH2 or MeO2CCHdCH2, K2CO3, nBu4NI, DMF, 80-90 °C;
for 22c, Pd(OAc)2, 3-NO2C6H4CHdCH2, PPh3, Et3N, reflux tem-
perature; for 23, terminal alkynes, Pd(PPh3)4, CuI, Et3N/MeCN,
reflux.
products were found to possess trans- configurations
(Scheme 9).
3-Alkynyl-4-phenylthiophenes 23 were readily obtained
in high yields by the Sonogashira coupling reaction38 of
3-iodo-4-phenylthiophene (21) with terminal alkynes
(Scheme 9). Due to the possible poisoning of the pal-
ladium catalyst caused by the thiophene sulfur, more
palladium catalyst (about 10% mol) had to be used. An
insufficient amount of catalyst did not lead to reaction.
Several 3-phenyl-4-arylthiophenes 24 were prepared
by the Suzuki cross-coupling reaction39 of 3-iodo-4-
phenylthiophene (21) with areneboronic acids in good
yields. As such, this procedure provides a general route
to unsymmetrical 3,4-diarylthiophenes. For example,
3-phenyl-4-(4′-methylphenyl)thiophene (24a ) was isolated
in 76% yield by reaction of 21 with 4-methylphenyl-
boronic acid in the presence of Pd(PPh3)4 catalyst and 2
M aqueous Na2CO3 in refluxing MeOH-PhMe (Table 2,
entry 1). Under similar conditions, the coupling reaction
utilizing mesitylboronic acid did not occur due to the
steric hindrance of the two o-methyl groups. The reaction
did not proceed well even when a stronger base Ba(OH)2
was used.42a Eventually, it was found that the base
tBuOK42b could lead to the coupling reaction in acceptable
yield (56%), affording 24d as a highly sterically hindered
thiophene (Table 2, entry 4).
Sch em e 10
Previous reports17c,d from our laboratory have unequivo-
cally demonstrated the usefulness of organoboroxines for
the synthesis of 3,4-disubstituted furans. To further
extend this pathway, we would like to investigate the
possibility of 3,4-disubstituted thiophene synthesis from
organoboroxines. As can be seen in Scheme 10, the
alkynylthiophenes 17 were first hydrogenated to 25 with
10% Pd-C catalyst in almost quantitative yields. Then,
alkylthiophenes 25 were converted to boroxines 26 by
treatment with boron trichloride and subsequent hy-
drolysis of the resulting dichloroboranes.
(Scheme 10, Table 3). For example, 27a was obtained
in 87% yield by reaction of the boroxine 26a with
9-bromophenanthrene in the presence of Pd(PPh3)4 cata-
lyst and 2 M Na2CO3 aqueous solution in reflux metha-
nol-toluene (Table 3, entry 1). When 26a was allowed
to react with 1,4-dibromobenzene under similar condi-
tions, two coupling products 27b and 27c were isolated
in 21% and 49% yields, respectively (Table 3, entry 2).
Somewhat surprisingly, the reaction of 2 equiv of borox-
ine 26a with 3,4-dibromothiophene afforded the mono-
coupling product 27e and the hydrolytic deboration
product 27f without any detectable amount of the bis-
coupling product (Table 3, entry 4). On the other hand,
the cross coupling of boroxine 26b and (E)-â-bromo-
styrene gave the corresponding product 27i with complete
retention of the alkene configuration (Table 3, entry 7).
In this way, a number of unsymmetrically 3,4-disubsti-
tuted thiophenes have been realized, which is in keeping
with our own route to 3,4-disubstituted furans.17bde,43
The cross-coupling of boroxine 26c with 9,10-bis-
(bromomethyl)phenanthrene using palladium catalyst in
The Suzuki-type coupling reaction17b,39 of boroxines 26
with aryl, vinyl, and benzylic halides readily took place
(40) Heck, R. F. In Palladium Reagents in Organic Synthesis;
Academic Press: New York, 1985; Chapter 6, pp 179-321. Dieck, H.
A.; Heck, R. F. J . Am. Chem. Soc. 1974, 96, 1133-1136. Daves, G. D.,
J r. In Advances in Metal-Organic Chemistry; Liebeskind, L. S., Ed.;
J AI Press: London, 1991; Vol. 2, pp 59-99. Cabri, W.; Candiani, I.;
Bedeschi, A. J . Org. Chem. 1992, 57, 3558-3563.
(41) J effery, T. Tetrahedron Lett. 1985, 26, 2667-2670. J effery, T.
Tetrahedron Lett. 1990, 31, 6641-6644.
(42) (a) Suzuki, A. Pure Appl. Chem. 1994, 66, 213-222. Campi, E.
M.; J ackson, W. R.; Marcuccio, S. M.; Naeslund, C. G. M. J . Chem.
Soc., Chem. Commun. 1994, 2395. (b) Zhang, H.-C.; Chan, K. S.
Tetrahedron Lett. 1996, 37, 1043-1044.
(43) Kaufmann, D. Chem. Ber. 1987, 120, 901-905.

Applications of 3,4-Bis(trimethylsilyl)thiophene
J . Org. Chem., Vol. 62, No. 7, 1997 1945
Ta ble 3. Su zu k i-Typ e Rea ction of Bor oxin es 26 w ith
Ha lid es
Sch em e 12
Sch em e 13
quaterthiophene 29 in 20% yield and the reduction
product 30 in 11% yield. Consequently, the palladium-
catalyzed self-coupling reaction of boroxines is expected
to provide a new entry to thiophene-3,4-diyl oligomers,
which are difficult or even impossible to realize otherwise.
In order to further broaden the synthetic scope of our
silicon protocol strategy, it is desirable that the trimeth-
ylsilyl group can be converted to a tri-n-butylstannyl
group; thus, the resulting tin compound can serve as a
key intermediate for a regiospecific synthesis of 3,4-
disubstituted thiophenes. For this purpose, tris[4-(phen-
ylethyl)thiophene-3-yl]boroxine (26c), prepared from the
corresponding 3-(phenylethyl)-4-(trimethylsilyl)thiophene
(25c) after displacement of the C-Si bond by the C-B
bond, was chosen in our attempts to replace the boroxine
unit directly via palladium-catalyzed Suzuki coupling17f
with tri-n-butylstannyl chloride. A combination of
Pd(PPh3)4 as catalyst (10 mol %), NaOMe as base, and
methanol-toluene as solvent was found to be effective
in furnishing tri-n-butylstannyl-substituted thiophene 31
(Scheme 13).
Sch em e 11a
a
Reagents and conditions: 9,10-bis(bromomethyl)phenan-
threne, Pd(PPh3)4, 2 M Na2CO3, MeOH/PhMe, reflux, 44% yield.
It is noteworthy that thiophene 31 is acid-sensitive.
When 31 was slowly chromatographed through a column
packed with silica gel, an almost complete protodestan-
nylation occurred, yielding 3-(phenylethyl)thiophene (32).
For this reason, 31 had to be isolated by flash chroma-
tography on silica gel using hexanes containing 1% (v/v)
of triethylamine as eluent.
the presence of 2 M Na2CO3 was also attempted. How-
ever, no desired cross-coupling product was isolated. The
only identifiable product obtained was the dimeric
thiophene 28 in 44% yield (Scheme 11). It was with no
surprise because similar outcomes were encountered in
our former work concerning furans.17d
Inspired by the successful synthesis of the thiophene-
3,4-diyl dimer 28, the regiospecific preparation of a
thiophene-3,4-diyl tetramer was subsequently sought.
Thus, as shown in Scheme 12, the dimer 27g, prepared
from the cross-coupling of a boroxine and a halide as
shown in Table 3, was converted to its corresponding
boroxine, and subsequent coupling reaction gave the
The carbonylative coupling reaction44 of 3-(phenyl-
ethyl)-4-(tri-n-butylstannyl)thiophene (31) with halides
resulted in the introduction of a carbonyl functional group
at the coupling juncture of the two partners. The
reaction was performed under a CO pressure of 25-30
psi. Thus, when 3-(phenylethyl)-4-(tri-n-butylstannyl)-
(44) Goure, W. F.; Wright, M. E.; Davis, P. D.; Labadie, S. S.; Stille,
J . K. J . Am. Chem. Soc. 1984, 106, 7500-7506.

1946 J . Org. Chem., Vol. 62, No. 7, 1997
Ye and Wong
Sch em e 14
considerable efforts have been devoted toward the syn-
thetic exploration of strained cyclic cumulenes in the last
decade. In the literature, the isolable 1,2,3-cyclonon-
atriene50 as well as the fugitive 1,2,3-cycloheptatriene51
and 1,2,3-cyclohexatriene52 have been registered. Very
recently, 1,2,3-cyclooctatriene as a reactive intermediate
has also been reported.53 Within this series, 1,2,3-
cyclopentatriene still remains unknown, but its struc-
tural features and energetics have been studied by
computation.50a
Sch em e 15
On the other hand, five-membered hetarynes have also
aroused widespread synthetic endeavor54 and theoretical
curiosity55 because of their inherent strain. Although
both 2,3-didehydrothiophene (37)56 and 3,4-didehy-
drothiophene (2),57 the most mentioned of the five-
membered hetarynes, had been suggested as reactive
intermediates by Wittig in the early 1960’s, the validity
of such a claim was soon questioned.54bc,58 Subsequently,
the hetaryne 37 was generated from flash vacuum
thermolysis (FVT) of thiophene-2,3-dicarboxylic anhy-
dride and accordingly trapped.59 By way of contrast,
evidence for the existence of 3,4-didehydrothiophene (2)
has never been obtained despite many experimental
attempts.54c,59ac,60-64 Thus, the question has remained
open for over 30 years.
thiophene (31) was allowed to react with benzyl bromide
under an atmosphere of CO (25-30 psi), catalyzed by Pd-
(PPh3)4 in THF at 50-60 °C, the carbonylated product
33 was obtained in 50% yield and was accompanied by
13% yield of bis[4-(phenylethyl)thiophene-3-yl] ketone
(34) (Scheme 14). As a result, a synthetic entry to
3-alkyl-4-acylthiophenes was therefore established. We
believe that this conversion is also suitable for other aryl
halides. The formation of 34 was likely due to the low
CO pressure, which implied that the stannylthiophene
31 could possibly participate in an oxidative-addition-
like reaction with palladium in the presence of carbon
monoxide.
Another pathway from which 3,4-unsymmetrically
substituted thiophenes could be made was by soliciting
a tin-lithium exchange reaction.45,46 The lithiation of
3-(phenylethyl)-4-(tri-n-butylstannyl)thiophene (31) with
n-butyllithium was carried out at -78 °C to ensure that
the â-lithiothiophene formed would not undergo rear-
rangement47 to the R-lithiothiophene. The tin-lithium
exchange reaction was monitored by TLC with the
appearance of tetrabutyltin and disappearance of the
starting organostannane. It is worthy to note that
organostannanes generally show large bright spots on
TLC plates in an iodine chamber. The lithiation was very
fast, usually reaching completion within 15 min (Scheme
15).
To make sure that the â-lithiothiophene 35 was indeed
formed, the reaction solution was quenched with an
excess of acetone, and as a result, the product thiophene
36a was isolated in 51% yield. Similarly, the trapping
reaction of 35 toward electrophiles DMF and phenylse-
lenenyl bromide resulted in the formation of aldehyde
36b and selenide 36c in 59% and 54% yields, respectively
(Scheme 15).
Recently, the use of phenyl[o-(trimethylsilyl)phenyl]-
iodonium triflate as a precursor for the efficient formation
of benzyne under mild and neutral conditions was
reported by Kitamura and Yamane.65 Encouraged by
(50) (a) Angus, R. O., J r.; J ohnson, R. P. J . Org. Chem. 1984, 49,
2880-2883. (b) Angus, R. O., J r.; J anakiraman, M. N.; J acobson, R.
A.; J ohnson, R. P. Organometallics 1987, 6, 1909-1912.
(51) Zoch, H.-G.; Szeimies, G.; Ro¨mer, R.; Schmitt, R. Angew. Chem.,
Int. Ed. Engl. 1981, 20, 877-878. Zoch, H.-G.; Szeimies, G.; Ro¨mer,
R.; Germain, G.; Declercq, J .-P. Chem. Ber. 1983, 116, 2285-2310.
(52) Shakespeare, W. C.; J ohnson, R. P. J . Am. Chem. Soc. 1990,
112, 8578-8579.
(53) Hernandez, S.; Kirchhoff, M. M.; Swartz, S. G., J r.; J ohnson,
R. P. Tetrahedron Lett. 1996, 37, 4907-4910.
(54) (a) Kauffmann, T.; Wirthwein, R. Angew. Chem., Int. Ed. Engl.
1971, 10, 20-33. (b) Reinecke, M. G. Tetrahedron 1982, 38, 427-498.
(c) Reinecke, M. G. In Reactive Intermediates; Abramovitch, R. A., Ed.;
Plenum Press: New York, 1982; Vol 2, pp 367-526.
(55) (a) Yonezawa, T.; Konishi, H.; Kato, H. Bull. Chem. Soc. J pn.
1969, 42, 933-942. (b) Radom, L.; Nobes, R. H.; Underwood, D. J .; Li,
W.-K. Pure Appl. Chem. 1986, 58, 75-88.
(56) Wittig, G.; Wahl, V. Angew. Chem. 1961, 73, 492.
(57) Wittig, G. Angew. Chem., Int. Ed. Engl. 1962, 1, 415-419.
(58) (a) Wittig, G. Pure Appl. Chem. 1963, 7, 173-191. (b) Hoffmann,
R. W. Dehydrobenzene and Cycloalkynes; Academic Press: New York,
1967; p 293.
(59) (a) Reinecke, M. G.; Newsom, J . G. J . Am. Chem. Soc. 1976,
98, 3021-3022. (b) Reinecke, M. G.; Chen, L.-J .; Almqvist, K. A. J .
Chem. Soc., Chem. Commun. 1980, 585-586. (c) Reinecke, M. G.;
Newsom, J . G.; Chen, L.-J . J . Am. Chem. Soc. 1981, 103, 2760-2769.
(d) Reinecke, M. G.; Newsom, J . G.; Almqvist, K. A. Tetrahedron 1981,
37, 4151-4157. (e) Teles, J . H.; Hess, B. A., J r.; Schaad, L. J . Chem.
Ber. 1992, 125, 423-431.
(60) (a) Moses, P.; Gronowitz, S. Arkiv Kemi 1961, 18, 119-132;
Chem. Abstr. 1962, 56, 10173c. (b) Christiansen, H.; Gronowitz, S.;
Rodmar, B.; Rodmar, S.; Rosen, U.; Sharma, M. K. Arkiv Kemi 1968,
30, 561-582; Chem. Abstr. 1969, 71, 26413c.
(61) Reinecke, M. G.; Adickes, H. W. J . Am. Chem. Soc. 1968, 90,
511-513.
(62) Stoyanovich, F. M.; Gol’dfarb, Y. L.; Chermanova, G. B. Izv.
Akad. Nauk SSSR, Ser. Khim. 1973, 2285-2290; Chem. Abstr. 1974,
80, 37201u.
(c) 3,4-Did eh yd r oth iop h en e. Structural limitations
in organic compounds have posed a longstanding chal-
lenge to chemists.48 Cyclic cumulenes49 are a fundamen-
tal class of strained hydrocarbons for which limiting ring
sizes are as yet unknown. Because of such curiosity,
(45) (a) Seyferth, D.; Weiner, M. A. J . Am. Chem. Soc. 1961, 83,
3583-3586. (b) Seyferth, D.; Weiner, M. A. J . Org. Chem. 1961, 26,
4797-4800. (c) Seyferth, D.; Weiner, M. A. J . Am. Chem. Soc. 1962,
84, 361-364.
(46) Yang, Y.; Wong, H. N. C. Tetrahedron 1994, 50, 9583-9608.
(47) Gronowitz, S. Chem. Heterocycl. Compds 1994, 30, 1252-1283.
(48) (a) Wiberg, K. Chem. Rev. 1989, 89, 975-983. (b) Warner, P.
M. Chem. Rev. 1989, 89, 1067-1093. (c) Borden, W. T. Chem. Rev.
1989, 89, 1095-1109. (d) Billups, W. E.; Haley, M. M.; Lee, G.-A. Chem.
Rev. 1989, 89, 1147-1159. (e) J ohnson, R. P. In Molecular Structures
and Energetics; Leibman, J . F., Greenberg, A., Eds.; VCH Publishers:
Deerfield Beach, FL, 1986; Vol. 3, pp 85-140.
(63) Ayers, B. E.; Longworth, S. W.; McOmie, J . F. W. Tetrahedron
1975, 31, 1755-1760.
(64) David, M. P.; McOmie, J . F. W. Tetrahedron Lett. 1973, 1361-
1362.
(65) Kitamura, T.; Yamane, M. J . Chem. Soc., Chem. Commun.
1995, 983-984.
(49) J ohnson, R. P. Chem. Rev. 1989, 89, 1111-1124.

Applications of 3,4-Bis(trimethylsilyl)thiophene
J . Org. Chem., Vol. 62, No. 7, 1997 1947
Sch em e 16a
Sch em e 17
Sch em e 18
ture of the known 9,10-adduct 39a 68 and the 1,4-adduct
39b was given in a total yield of only 10%. The
structures and ratio (2.7:1) of 39a and 39b were con-
1
firmed by H- and 13C-NMR spectral analyses. Careful
partial recrystallization of a mixture of 39a and 39b from
MeOH nonetheless afforded a pure sample of 39a , mp
267-268 °C (lit.68 mp 268 °C). Lower reaction temper-
atures were found to cause no significant effect on the
yield and ratio of the products. In a similar manner,
when naphthalene was used as a trapping reagent,
adduct 40 was isolated in a meager 6% yield. Compelling
evidence for 2’s remarkable reactivity was obtained by
its reaction with benzene, which yielded the adduct 41
in a low 7% yield. Moreover, the reaction of 2 with 2,3-
dimethyl-1,3-butadiene unexpectedly gave in 27% total
yield a chromatographically separable mixture (silica gel,
n-pentane) of a [2 + 2] adduct 42a , as well as an ene
reaction product 42b, in the ratio of 1:1. The isolation
of 42b is consistent with the observation that ene reaction
generally competes with cycloaddition in a trapping
process comprising a distorted π-system and an alkene
having allylic hydrogen atoms (Scheme 17).69 The [2 +
2]-cycloaddition was also performed by reaction of 2 with
acrylonitrile, and expectedly, the [2 + 2] adduct 43 was
obtained in 13% yield. In other Diels-Alder reactions,
furan, 2-methylfuran, and 2,5-dimethylfuran were all
proved to react readily with 2 to supply adducts 44a , 44b,
and 44c, in 31%, 17%, and 13% yields, respectively. The
disappointingly low yields of the aforementioned trapping
reactions were most probably due to the side reaction in
which 2 reacted also with the iodobenzene generated from
38 through the elimination reaction.
It appeared that 2 did not dimerize to provide cy-
clobuta[1,2-c:3,4-c′]dithiophene (45),70 even for the condi-
tion in which no trapping reagent was involved. How-
ever, interestingly, when an 1 M nBu4NF in THF solution
was used instead of KF and 18-crown-6, an unexpected
product 46 was isolated in 6% yield. This result implies
that 2 may possibly possess some degree of diradical
character and is able to cleave the C-O bond of a THF
molecule (Scheme 18). Further studies on this aspect will
be attractive.
In summary, evidence for 3,4-didehydrothiophene (2)
as an intermediate has been procured by the formation
of its [2 + 2]- and [4 + 2]-cycloaddition adducts with
alkenes. It is believed that the five-membered 2 is the
smallest cyclic cumulene ever characterized.
a
Reagents and conditions: (a) KF, 18-crown-6, CH2Cl2, room
temperature; (b) anthracene; (c) naphthalene; (d) benzene; (e) 2,3-
dimethyl-1,3-butadiene; (f) acrylonitrile; (g) furan, 2-methylfuran,
or 2,5-dimethylfuran.
their result, we were interested in exploring the genera-
tion of 3,4-didehydrothiophene (2) by virtue of this
method, which involved the fluoride-induced vicinal
elimination of the trimethylsilyl group and a good leaving
group.66
The precursor of 2, a diaryliodonium salt,67 namely,
phenyl[4-(trimethylsilyl)thien-3-yl]iodonium triflate (38),
was prepared from 3,4-bis(trimethylsilyl)thiophene (1a )
according to the literature procedure.65 Thus, treatment
of 1a with iodobenzene diacetate in the presence of
trifluoromethanesulfonic acid gave 38 in 53% yield
(Scheme 16). The crystalline product 38 is quite stable
(mp 169-172 °C) at room temperature and can be stored
for extended periods.
The identity of 38 is unequivocally vindicated by its
1H NMR spectrum, which exhibited absorptions at δ 0.28
(s, 9H) for the trimethylsilyl protons, 7.43 (t, J ) 6.5, 6.5
Hz, 2H), 7.52 (dd, J ) 6.7, 1.1 Hz, 1H), and 7.80 (d, J )
6.4 Hz, 2H) for the phenyl protons, 7.55 (d, J ) 2.9 Hz,
1H) and 8.51 (d, J ) 2.9 Hz, 1H) for the 5- and 2-position
protons of the thiophene ring, respectively. The structure
of 38 was also supported by its 13C NMR, mass spectrum,
and a correct elemental analysis.
Addition of anhydrous potassium fluoride to a dichlo-
romethane solution of 38 in the presence of 18-crown-6
as anticipated generated cumulene 2, whose presence
was convincingly endorsed by its trapping reactions with
several alkenes as shown in Scheme 16.
Such a trapping exercise was first explored by generat-
ing 2 at room temperature in the presence of anthracene.
In this manner, a chromatographically inseparable mix-
(68) De Wit, J .; Wynberg, H. Tetrahedron 1973, 29, 1379-1391.
(69) Wittig, G.; Du¨rr, H. Liebigs Ann. Chem. 1964, 672, 55-62.
Crews, P.; Beard, J . J . Org. Chem. 1973, 38, 522-528.
(70) Shepherd, M. K. J . Chem. Soc., Chem. Commun. 1985, 880-
881.
(66) (a) Chan, T. H.; Massuda, D. Tetrahedron Lett. 1975, 3383-
3386. (b) Chan, T. H.; Massuda, D. J . Am. Chem. Soc. 1977, 99, 936-
937.
(67) Stang, P. J .; Zhdankin, V. V. Chem. Rev. 1996, 96, 1123-1178.

1948 J . Org. Chem., Vol. 62, No. 7, 1997
Ye and Wong
(c) 3,4-Bis(t r im et h ylsilyl)t h iop h en e (1a ). To dihy-
drothiophene 9 (230 mg, 1 mmol) in chloroform (8 mL) was
added a hot solution of DDQ (363 mg, 1.6 mmol) in chloroform
(45 mL). The mixture was stirred at 60-65 °C for 10 h. The
cooled reaction mixture was washed with aqueous sodium
carbonate (10%, 3 × 10 mL) and water (10 mL), dried (Na2-
SO4), and concentrated under reduced pressure. The residue
was purified by column chromatography on silica gel (30 g,
hexanes) to afford 1a (173 mg, 76%) as a colorless oil: 1H NMR
(CDCl3) δ 0.34 (s, 18H) and 7.61 (s, 2H); 13C NMR (CDCl3) δ
1.09, 134.73, and 145.43; MS m/z 228 (M+, 19). Anal. Calcd
for C10H20SSi2: C, 52.56; H, 8.82. Found: C, 52.36; H, 8.82.
The spectrometric data are identical to those reported in the
literature.18
3,4-Bis(tr im eth ylsilyl)th iop h en e (1a ). Meth od B. 3,4-
Dibromothiophene (11)19 (3.87 g, 16 mmol), dry THF (16 mL),
chlorotrimethylsilane (4.56 mL, 3.91 g, 36 mmol), and mag-
nesium powder (0.86 g, 36 mmol) were placed in a sealed tube
(15 cm length, 2.5 cm diameter). The tube was located in the
middle of an ultrasonic bath (Branson 1210, power supply 143
W, output power 35 W) so that the bottom of the tube was 1
cm above the bottom of the bath. The reaction mixture was
kept under ultrasonication for 4 days. The reaction course was
monitored by TLC. After completion of the reaction, the
reaction mixture was diluted with hexanes (160 mL) and ice-
water (40 mL), and the solids were filtered. The filtrate was
separated, and the water layer was extracted with hexanes (3
× 30 mL). The combined hexanes solution was dried over
MgSO4, and the solvent was evaporated. The residue was
chromatographed on silica gel (150 g, hexanes) to give an
inseparable mixture of 3,4-bis(trimethylsilyl)thiophene (1a )
and 3-bromo-4-(trimethylsilyl)thiophene.
To this mixture in a sealed tube (15 cm length, 2.5 cm
diameter) were added dry THF (16 mL), chlorotrimethylsilane
(2.28 mL, 1.95 g, 18 mmol), and magnesium powder (0.43 g,
18 mmol). The reaction was carried out under ultrasonication
as described above for 3 days. After the same workup, a pure
sample of 1a (1.09 g, 30%) was obtained as a colorless oil,
which was identical spectrometrically to an authentic sample
prepared by method A.
Gen er a l P r oced u r e for P r ep a r a tion of 1a -e. (a ) 3,4-
Bis(tr im eth ylsilyl)th iop h en e (1a ). A mixture of 4-phen-
ylthiazole (12b)34b (9.7 g, 60 mmol), bis(trimethylsilyl)acetylene
(13a ) (11.1 g, 65 mmol), and DBU (1.5 mL) was placed in a
tube (15 × 2.5 cm2) that was then attached to a vacuum
manifold (0.05 mmHg) and subjected to three freeze-thaw
cycles (liquid nitrogen). The tube was then sealed and heated
at 325 °C for 6 days. The resulting dark mixture was
chromatographed on a silica gel column (250 g, hexanes; then
hexanes-EtOAc 10:1 to 5:1) to give the recovered 12b (3.4 g)
and 1a (8.2 g, 92% based on reacted 12b) as a colorless oil.
Compound 1a was identical spectrometrically to an authentic
sample prepared by method A.
Con clu sion
In this study, we have described the efficient and
stepwise procedures for the realization of a number of
unsymmetrically 3,4-disubstituted thiophenes utilizing
3,4-bis(trimethylsilyl)thiophene (1a ) as a precursor.
3,4-Bis(trimethylsilyl)thiophene (1a ) underwent con-
secutive regiospecific mono-ipso-iodination and palladium-
catalyzed cross-coupling reactions such as the Stille
reaction, Sonogashira reaction, Heck reaction, and
Suzuki reaction to provide a number of unsymmetrically
3,4-disubstituted thiophenes.
The silylthiophenes were also converted to the corre-
sponding boroxines by an ipso replacement of a boron
moiety, which underwent a smooth Suzuki-type cross-
coupling reaction with organohalides to furnish 3,4-
disubstituted thiophenes with diverse substituents as
well.
By utilization of the palladium-catalyzed self-coupling
reaction of organoboroxines, thiophene-3,4-diyl dimer 28
and thiophene-3,4-diyl tetramer 29 were realized.
Tris[4-(phenylethyl)thiophene-3-yl]boroxine (26c) was
converted successfully to 3-(phenylethyl)-4-(tri-n-butyl-
stannyl)thiophene (31) through the palladium-catalyzed
cross-coupling reaction with tri-n-butylstannyl chloride.
The stannylthiophene (31) underwent carbonylative cou-
pling reaction to give thienyl ketones. On the other hand,
regiospecific lithiation of 31 provided the intermediate
â-lithiothiophene 35, which was quenched by several
electrophiles to afford various unsymmetrically 3,4-
disubstituted thiophenes.
As an important application, 3,4-bis(trimethylsilyl)-
thiophene (1a ) was successfully converted to phenyl[4-
(trimethylsilyl)thien-3-yl]iodonium triflate (38). This
iodonium salt 38 was then treated with fluoride to
generate 3,4-didehydrothiophene (2), which was trapped
by its [2 + 2]- and [4 + 2]-cycloaddition reactions with
several alkenes.
Exp er im en ta l Section
3,4-Bis(tr im eth ylsilyl)th iop h en e (1a ). Meth od A. (a )
Bis(tr im eth ylsilylm eth yl)su lfoxid e (4).21 To a solution of
acetonitrile (3 mL) containing bis[(trimethylsilyl)methyl] sul-
fide (8)24a (206 mg, 1 mmol) in a 50-mL round-bottomed flask
was added an aqueous solution of sodium metaperiodate (257
mg, 1.2 mmol) in water (3 mL) at -10 °C by ice-salt bath
cooling. The solution was stirred at -10 to 0 °C for 12 h, and
then the cold solution was filtered and extracted with cold
dichloromethane (3 × 5 mL). The dichloromethane extracts
were dried (Na2SO4) and concentrated under vacuum to yield
4 as a colorless oil that is pure enough to be used in the
subsequent reaction without further purification: 1H NMR
(CDCl3) δ 0.22 (s, 18H), 2.14 (d, J ) 13.4 Hz, 2H), 2.45 (d, J )
13.7 Hz, 2H). The spectroscopic data coincide with the
previous report.21
(b) 3,4-Bis(tr im eth ylsilyl)-2,5-d ih yd r oth iop h en e (9). In
a flame dried 100-mL three-necked round-bottomed flask
equipped with a water condenser and a dropping funnel was
added a solution of 4 (666 mg, 3 mmol) and bis(trimethylsilyl)-
acetylene (13a ) (340 mg, 2 mmol) in dry HMPA (2 mL)
(distilled from CaH2) rapidly from a dropping funnel to dry
HMPA (2 mL), and the resulting solution was warmed at 100
°C and stirred at this temperature for half an hour under
nitrogen atmosphere. The cooled reaction mixture was diluted
with benzene (40 mL), washed with brine (4 × 15 mL), and
dried over MgSO4. The solvent was removed under reduced
pressure. The residue was subjected to column chromatogra-
phy on silica gel (50 g, hexanes) to give 9 (69 mg, 15%) as a
colorless oil: 1H NMR (CDCl3) δ 0.21 (s, 18H), 4.06 (s, 4H);
13C NMR (CDCl3) δ 0.84, 50.44, 150.77; ΜS m/z 230 (M+, 21);
high-resolution MS Calcd for C10H22SSi2 m/z 230.0982, found
230.0981.
(b) 3,4-Bis(tr im eth ylsilyl)th iop h en e (1a ). A mixture of
4-methylthiazole (12a ) (300 mg, 3.0 mmol), 13a (500 mg, 2.9
mmol), and triethylamine (0.1 mL) in a sealed tube (14 × 1.25
cm2) was heated at 360 °C for 2.5 days to give 1a (128 mg,
19%) that was identical spectrometrically to an authentic
sample prepared previously.
(c) 3-Meth yl-4-(tr im eth ylsilyl)th iop h en e (1b). A mix-
ture of 12a (3.0 g, 30 mmol), 1-(trimethylsilyl)propyne (3.4 g,
30 mmol), and DBU (0.75 mL) in a sealed tube (14.5 × 2 cm2)
was heated at 340 °C for 4 days. Chromatography on silica
gel (300 g, n-pentane; then n-pentane-ether 4:1) gave the
recovered 12a (1.7 g) and 1b (716 mg, 32% based on reacted
12a ) as a colorless oil. For thiophene 1b: 1H NMR (CDCl3) δ
0.30 (s, 9H), 2.37 (d, J ) 1.0 Hz, 3H), 6.98 (dq, J ) 2.8, 1.0,
1.0, 1.0 Hz, 1H), 7.36 (d, J ) 2.8 Hz, 1H); 13C NMR (CDCl3) δ
-0.52, 16.78, 121.92, 132.92, 141.17, 142.20; MS m/z 170 (M+,
20). Anal. Calcd for C8H14SSi: C, 56.41; H, 8.28. Found: C,
56.34; H, 8.17.
(d ) 3-(Tr im eth ylsilyl)th iop h en e (1c). A mixture of 12b
(4.83 g, 30 mmol), ethynyltrimethylsilane (3.30 g, 33.6 mmol),
and DBU (0.75 mL) in a sealed tube (14.5 × 2 cm2) was heated
at 340 °C for 2 days. Chromatography on silica gel (300 g,
n-pentane; then hexanes-EtOAc 10:1-5:1) gave the recovered
12b (2.67 g) and 1c (1.36 g, 65% based on reacted 12b) as a

Applications of 3,4-Bis(trimethylsilyl)thiophene
J . Org. Chem., Vol. 62, No. 7, 1997 1949
colorless oil. For thiophene 1c: 1H NMR (CDCl3) δ 0.28 (s,
9H), 7.20 (dd, J ) 4.8, 1.1 Hz, 1H), 7.40 (dd, J ) 4.8, 2.6 Hz,
1H), 7.45 (dd, J ) 2.6, 1.1 Hz, 1H); 13C NMR (CDCl3) δ -0.57,
125.58, 131.37, 134.73, 141.27; MS m/z 156 (M+, 7). The
spectroscopic data coincide with the previous report.27c
(e) 3-n -Bu tyl-4-(tr im eth ylsilyl)th iop h en e (1d ). A mix-
ture of 12b (4.83 g, 30 mmol), 1-(trimethylsilyl)-1-hexyne (4.62
g, 30 mmol), and DBU (0.75 mL) in a sealed tube (14.5 × 2
cm2) was heated at 330 °C for 7 days. Chromatography on
silica gel (300 g, hexanes containing 1% Et3N; then hexanes-
EtOAc 10:1 to 5:1) gave the recovered 12b (2.85 g) and 1d (1.90
g, 73% based on reacted 12b) as a colorless oil. For thiophene
1d : 1H NMR (CDCl3) δ 0.28 (s, 9H), 0.95 (t, J ) 7.2, 7.2 Hz,
3H), 1.38-1.68 (m, 4H), 2.69 (dt, J ) 0.8, 7.8, 7.8 Hz, 2H),
Gen er a l P r oced u r e for P r ep a r a tion of Th iop h en es
17a -j by th e Son oga sh ir a Cou p lin g Rea ction . (a ) 3-(Tr i-
m eth ylsilyl)-4-(h ep tyn -1′-yl)th iop h en e (17a ). A mixture
consisting of 14 (141 mg, 0.5 mmol), 1-heptyne (96 mg, 1.0
mmol), Pd(PPh3)4 (58 mg, 0.05 mmol), copper(I) iodide (19 mg,
0.1 mmol), dry acetonitrile (2 mL), and dry triethylamine (5
mL) was stirred at reflux temperature (nitrogen atmosphere)
for 18 h. The solvent was removed under reduced pressure,
and the residue was subjected to column chromatography on
silica gel (20 g, hexanes) to give 17a (110 mg, 88%) as an oil:
1H NMR (CDCl3) δ 0.32 (s, 9H), 0.91 (t, J ) 7.0, 7.0 Hz, 3H),
1.33-1.45 (m, 4H), 1.55-1.60 (m, 2H), 2.40 (t, J ) 7.1, 6.9
Hz, 2H), 7.29 (d, J ) 2.8 Hz, 1H), 7.40 (d, J ) 2.8 Hz, 1H); 13
C
NMR (CDCl3) δ -1.07, 13.92, 19.40, 22.22, 28.40, 31.21, 90.97,
127.55, 128.84, 131.61, 142.93; MS m/z 250 (M+, 41). Anal.
Calcd for C14H22SSi: C, 67.13; H, 8.85. Found: C, 66.61; H,
8.86.
6.99 (dt, J ) 2.8, 0.8, 0.8 Hz, 1H), 7.35 (d, J ) 2.8 Hz, 1H); 13
C
NMR (CDCl3) δ -0.16, 13.97, 22.70, 30.63, 32.75, 120.66,
132.66, 140.98, 147.83; MS m/z 212 (M+, 28). Anal. Calcd for
C11H20SSi: C, 62.20; H, 9.49. Found: C, 62.10; H, 9.57.
(f) 3,4-Dip h en ylth iop h en e (1e). A mixture of 12b (322
mg, 2 mmol) and diphenylacetylene (356 mg, 2 mmol) in a
sealed tube (14 × 1.25 cm2) was heated at 340 °C for 2.5 days
to give the recovered 12b (280 mg) and 1e (51 mg, 83% based
on reacted 12b) as colorless crystals. For thiophene 1e: mp
115-116 °C (lit.10a 112-113 °C; lit.71 mp 114 °C); 1H NMR
(CDCl3) δ 7.16-7.26 (m, 10H), 7.29 (s, 2H); 13C NMR (CDCl3)
δ 123.98, 126.87, 128.13, 129.05, 136.65, 141.86; ΜS m/z 236
(M+, 100).
(b) 3-(Tr im eth ylsilyl)-4-(n on yn -1′-yl)th iop h en e (17b).
This was prepared from 14 (141 mg, 0.5 mmol) and 1-nonyne
(93 mg, 0.75 mmol) in the same manner as described for 17a ,
yielding 17b (124 mg, 89%) as an oil: 1H NMR (CDCl3) δ 0.32
(s, 9H), 0.89 (t, J ) 6.8, 6.6 Hz, 3H), 1.30-1.35 (m, 6H), 1.38-
1.47 (m, 2H), 1.55-1.63 (m, 2H), 2.40 (t, J ) 7.1, 6.9 Hz, 2H),
7.30 (d, J ) 2.9 Hz, 1H), 7.40 (d, J ) 2.9 Hz, 1H); 13C NMR
(CDCl3) δ -1.06, 14.06, 19.45, 22.64, 28.75, 28.86, 29.03, 31.79,
91.00, 127.54, 128.85, 131.64, 142.93; MS m/z 278 (M+, 28).
Anal. Calcd for C16H26SSi: C, 69.00; H, 9.41. Found: C, 69.25;
H, 9.73.
4-Iod o-3-(tr im eth ylsilyl)th iop h en e (14). Thiophene 1a
(1.82 g, 8 mmol) in THF (120 mL) under nitrogen was cooled
in a dry ice-acetone bath to -78 °C. Silver trifluoroacetate
(3.54 g, 16 mmol) was added, and the mixture was stirred for
5 min to ensure complete dissolution. Then iodine (4.06 g, 16
mmol) in THF (60 mL) was added dropwise, and the reaction
mixture was stirred at -78 °C for 8 h after the addition was
finished. The reaction mixture was diluted with ether (150
mL) and filtered through Celite. The filter cake was washed
with ether (50 mL). The filtrates were washed with 50%
sodium thiosulfate solution (2 × 80 mL), dried over MgSO4,
and concentrated under reduced pressure. The residue was
purified by chromatography on silica gel (150 g, hexanes) to
give 14 (2.16 g, 96%) as a colorless oil: 1H NMR (CDCl3) δ
0.37 (s, 9H), 7.31 (d, J ) 2.9 Hz, 1H), 7.51 (d, J ) 2.9 Hz, 1H);
13C NMR (CDCl3) δ -0.65, 83.18, 130.39, 133.87, 144.69; MS
m/z 282 (M+, 32); high-resolution MS calcd for C7H11SISi m/z
281.9392, found 281.9381.
Gen er a l P r oced u r e for P r ep a r a tion of 15 a n d 16 by
th e Stille Cou p lin g Rea ction . (a ) 3-(Tr im eth ylsilyl)-4-
eth yn ylth iop h en e (15). To a mixture of 14 (705 mg, 2.5
mmol) and ethynyltri-n-butyltin72 (788 mg, 2.5 mmol) in
dioxane (30 mL) was added Pd(PPh3)4 (290 mg, 0.25 mmol).
The resulting mixture was heated at 90 °C for 6 h under a
nitrogen atmosphere. The cooled reaction mixture was diluted
with ether (150 mL), washed with water (2 × 25 mL), and dried
over MgSO4. After removal of the solvent, the residue was
purified by column chromatography on silica gel (150 g,
n-pentane) to give 15 (406 mg, 90%) as a colorless oil: 1H NMR
(CDCl3) δ 0.34 (s, 9H), 3.12 (s, 1H), 7.32 (d, J ) 2.8 Hz, 1H),
7.59 (d, J ) 2.8 Hz, 1H); 13C NMR (CDCl3) δ -1.08, 78.13,
80.37, 125.69, 131.67, 131.92, 143.35; MS m/z 180 (M+, 22).
Anal. Calcd for C9H12SSi: C, 59.94; H, 6.71. Found: C, 60.17;
H, 6.84.
(c) 3-(Tr im eth ylsilyl)-4-(ph en yleth yn yl)th ioph en e (17c).
This was prepared from 14 (141 mg, 0.5 mmol) and phenyl-
acetylene (76 mg, 0.75 mmol) in the same manner as described
for 17a , yielding 17c (109 mg, 85%) as a colorless thick oil:
1H NMR (CDCl3) δ 0.37 (s, 9H), 7.30-7.35 (m, 4H), 7.48-7.52
(m, 2H), 7.57 (d, J ) 2.9 Hz, 1H); 13C NMR (CDCl3) δ -7.99,
79.17, 82.99, 116.56, 119.72, 121.07, 121.38, 122.99, 124.21,
124.99, 136.09; MS m/z 256 (M+, 37). Anal. Calcd for C15H16
-
SSi: C, 70.26; H, 6.29. Found: C, 70.51; H, 6.26.
(d ) 3-(Tr im et h ylsilyl)-4-(cycloh exen -1′-yl)t h iop h en e
(17d ). This was prepared from 14 (141 mg, 0.5 mmol) and
1-ethynylcyclohexene (80 mg, 0.75 mmol) in the same manner
as described for 17a , yielding 17d (114 mg, 88%) as a colorless
oil: 1H NMR (CDCl3) δ 0.34 (s, 9H), 1.59-1.69 (m, 4H), 2.10-
2.22 (m, 4H), 6.14-6.18 (m, 1H), 7.31 (d, J ) 2.8 Hz, 1H), 7.44
(d, J ) 2.8 Hz, 1H); 13C NMR (CDCl3) δ -1.06, 21.55, 22.35,
25.74, 29.04, 83.38, 91.85, 120.86, 127.21, 129.03, 131.73,
134.32, 142.94; MS m/z 260 (M+, 42). Anal. Calcd for C15H20
-
SSi: C, 69.17; H, 7.74. Found: C, 69.31; H, 7.66.
(e) 3-(Tr im eth ylsilyl)-4-[(1′-h yd r oxycyclop en tyl)eth yn -
yl]th iop h en e (17e). This was prepared from 14 (141 mg, 0.5
mmol) and 1-ethynylcyclopentanol (82.5 mg, 0.75 mmol) in the
same manner as described for 17a . Chromatography on silica
gel (20 g, hexanes-EtOAc 6:1) gave 17e (123 mg, 93%) as an
oil: 1H NMR (CDCl3) δ 0.33 (s, 9H), 1.76-1.91 (m, 4H), 2.01-
2.06 (m, 5H), 7.31 (d, J ) 2.9 Hz, 1H), 7.48 (d, J ) 2.8 Hz,
1H); 13C NMR (CDCl3) δ -1.10, 23.39, 42.26, 74.88, 79.74,
93.43, 126.23, 130.01, 131.84, 142.84; MS m/z 264 (M+, 13).
Anal. Calcd for C14H20OSSi: C, 63.58; H, 7.62. Found: C,
63.46; H, 7.64.
(f) 3-(Tr im eth ylsilyl)-4-(4′-h ydr oxybu tyn -1′-yl)th ioph en e
(17f). This was prepared from 14 (141 mg, 0.5 mmol) and
3-butyn-1-ol (52.5 mg, 0.75 mmol) in the same manner as
described for 17a . Chromatography on silica gel (20 g,
hexanes-EtOAc 3.5:1) gave 17f (103 mg, 92%) as an oil: 1H
NMR (CDCl3) δ 0.31 (s, 9H), 2.12 (br. s, 1H), 2.67 (t, J ) 6.4,
6.4 Hz, 2H), 3.80 (t, J ) 6.4, 6.4 Hz, 2H), 7.30 (d, J ) 2.9 Hz,
1H), 7.44 (d, J ) 2.9 Hz, 1H); 13C NMR (CDCl3) δ -1.09, 23.78,
61.11, 78.92, 86.97, 126.69, 129.64, 131.81, 142.87; MS m/z 224
(M+, 82). Anal. Calcd for C11H16OSSi: C, 58.88; H, 7.19.
Found: C, 58.37; H, 7.34.
(b) Bis[4-(tr im eth ylsilyl)th ien -3-yl]a cetylen e (16).
A
mixture of 14 (70.5 mg, 0.25 mmol), bis(tri-n-butylstannyl)-
acetylene (75.5 mg, 0.125 mmol), and Pd(PPh3)4 (29 mg, 0.025
mmol) in dioxane (3 mL) and triethylamine (1 mL) was heated
at 90 °C for 8 h under nitrogen. Chromatography on silica
gel (20 g, hexanes containing 2% Et3N) afforded 16 (23.5 mg,
56%) as pale yellowish crystals: mp 69-71 °C; 1H NMR
(CDCl3) δ 0.37 (s, 18H), 7.37 (d, J ) 2.9 Hz, 2H), 7.52 (d, J )
2.9 Hz, 2H); 13C NMR (CDCl3) δ -0.92, 86.76, 127.07, 129.41,
131.98, 143.08; MS m/z 334 (M+, 100). Anal. Calcd for
C16H22S2Si2: C, 57.43; H, 6.63. Found: C, 57.48; H, 6.75.
(g) 3-(Tr im et h ylsilyl)-4-(6′-h yd r oxyh exyn -1′-yl)t h io-
p h en e (17g). This was prepared from 14 (141 mg, 0.5 mmol)
and 5-hexyn-1-ol (73.5 mg, 0.75 mmol) in the same manner
as described for 17a . Chromatography on silica gel (20 g,
hexanes-EtOAc 4:1) gave 17g (115 mg, 91%) as an oil: 1H
NMR (CDCl3) δ 0.32 (s, 9H), 1.66-1.73 (m, 4H), 2.17 (br. s,
1H), 2.44 (t, J ) 6.6, 6.5 Hz, 2H), 3.67 (t, J ) 6.1, 6.0 Hz, 2H),
7.29 (d, J ) 2.9 Hz, 1H), 7.40 (d, J ) 2.8 Hz, 1H); 13C NMR
(71) Hinsberg, O. Ber. 1915, 48, 1611-1614; Chem. Abstr. 1916, 10,
63.
(72) Bottaro, J . C.; Hanson, R. N.; Seitz, D. E. J . Org. Chem. 1981,
46, 5221-5222.

1950 J . Org. Chem., Vol. 62, No. 7, 1997
Ye and Wong
(CDCl3) δ -1.08, 19.18, 24.96, 31.95, 62.27, 77.36, 90.38,
127.28, 129.01, 131.66, 142.81; MS m/z 252 (M+, 22). Anal.
Calcd for C13H20OSSi: C, 61.85; H, 7.99. Found: C, 61.82; H,
8.03.
5.4 Hz, 2H), 7.33-7.37 (m, 4H), 7.46 (d, J ) 3.2 Hz, 1H), 7.52-
7.56 (m, 2H); 13C NMR (CDCl3) δ 24.00, 61.07, 83.35, 88.91,
91.45, 123.05, 124.96, 125.11, 127.62, 128.04, 128.39, 131.64;
MS m/z 252 (M+, 71). Anal. Calcd for C16H12OS: C, 76.16;
H, 4.79. Found: C, 76.33; H, 4.63.
(h ) 3-(Tr im eth ylsilyl)-4-[3′-(ben zylm eth yla m in o)p r op -
yn -1′-yl]th iop h en e (17h ). This was prepared from 14 (141
mg, 0.5 mmol) and N-benzyl-N-methylpropargylamine (119
mg, 0.75 mmol) in the same manner as described for 17a .
Chromatography on silica gel (20 g, hexanes-EtOAc 6:1) gave
17h (143 mg, 91%) as an oil: 1H NMR (CDCl3) δ 0.35 (s, 9H),
2.39 (s, 3H), 3.54 (s, 2H), 3.64 (s, 2H), 7.28-7.35 (m, 6H), 7.52
(d, J ) 2.8 Hz, 1H); 13C NMR (CDCl3) δ -0.95, 41.94, 46.00,
60.32, 81.94, 85.47, 126.67, 127.11, 128.25, 129.10, 130.26,
131.84, 138.62, 142.76; MS m/z 313 (M+, 44). Anal. Calcd for
C18H23NSSi: C, 68.95; H, 7.39; N, 4.47. Found: C, 68.98; H,
7.70; N, 4.00.
4-P h en yl-3-(tr im eth ylsilyl)th iop h en e (20). To a stirred
solution containing 14 (1.41 g, 5 mmol), phenylboronic acid
(0.61 g, 5 mmol), and Pd(PPh3)4 (288 mg, 0.25 mmol) in
methanol-toluene (1:1, 160 mL) was added a 2 M Na2CO3
aqueous solution (20 mL). The reaction mixture was heated
at reflux for 5 h under nitrogen and was then poured into ice-
water (200 mL). The resulting mixture was extracted with
ether (3 × 250 mL). The combined ether extracts were dried
over MgSO4
, and the solvent was removed. The residue was
purified by chromatography on silica gel (150 g, hexanes) to
give 20 (0.89 g, 77%) as colorless crystals: mp 59-62 °C;
1H
NMR (CDCl3) δ 0.24 (s, 9H), 7.36 (d, J ) 2.9 Hz, 1H), 7.49-
7.53 (m, 5H), 7.63 (d, J ) 2.9 Hz, 1H); 13C NMR (CDCl3) δ
0.14, 123.51, 127.15, 127.85, 129.29, 133.33, 139.10, 141.13,
148.78; MS m/z 232 (M+, 44). Anal. Calcd for C13H16SSi: C,
67.18; H, 6.94. Found: C, 67.16; H, 6.94.
(i) 3-(Tr im et h ylsilyl)-4-(cis-5′-h yd r oxy-3′-m et h yl-3′-
p en ten -1′-yn yl)th iop h en e (17i). This was prepared from 14
(141 mg, 0.5 mmol) and cis-3-methyl-2-penten-4-yn-1-ol (72
mg, 0.75 mmol) in the same manner as described for 17a .
Chromatography on silica gel (20 g, hexanes-EtOAc 5:1) gave
17i (92 mg, 74%) as an oil: 1H NMR (CDCl3) δ 0.35 (s, 9H),
1.91 (br s, 1H), 1.97 (q, J ) 1.2, 1.2, 1.2 Hz, 3H), 4.40 (d, J )
6.7 Hz, 2H), 5.90 (tq, J ) 6.8, 6.8, 1.5, 1.5, 1.5 Hz, 1H), 7.34
(d, J ) 2.9 Hz, 1H), 7.51 (d, J ) 2.7 Hz, 1H); 13C NMR (CDCl3)
δ -1.08, 23.00, 61.41, 88.04, 91.05, 120.78, 126.41, 130.26,
3-Iod o-4-p h en ylth iop h en e (21). Thiophene 20 (58 mg,
0.25 mmol) in THF-MeOH (5:1, 8 mL) under nitrogen was
cooled to -78 °C. Silver trifluoroacetate (111 mg, 0.5 mmol)
was added, and the mixture was stirred for 5 min to ensure
complete dissolution. Then iodine (127 mg, 0.5 mmol) in
THF-MeOH (5:1, 6 mL) was added dropwise. The reaction
mixture was stirred at -78 °C for 4 h after the addition was
finished and then warmed to room temperature for 20 h. The
usual workup as described for 14 gave 21 (48 mg, 67%) as
132.04, 135.22, 142.75; MS (CI) m/z 250 (M+, 20), 249 (M+
-
1, 100). Anal. Calcd for C13H18OSSi: C, 62.35; H, 7.24.
Found: C, 62.50; H, 7.37.
(j) 3-(Tr im eth ylsilyl)-4-(tr a n s-5′-h yd r oxy-3′-m eth yl-3′-
p en ten -1′-yn yl)th iop h en e (17j). This was prepared from 14
(141 mg, 0.5 mmol) and trans-3-methyl-2-penten-4-yn-1-ol (72
mg, 0.75 mmol) in the same manner as described for 17a .
Chromatography on silica gel (20 g, hexanes-EtOAc 5:1) gave
17j (85 mg, 68%) as an oil: 1H NMR (CDCl3) δ 0.33 (s, 9H),
1.62 (br. s, 1H), 1.92 (m, 3H), 4.28 (d, J ) 6.8 Hz, 2H), 6.05
(tq, J ) 6.8, 6.8, 1.4, 1.4, 1.4 Hz, 1H), 7.33 (d, J ) 2.8 Hz, 1H),
7.49 (d, J ) 2.8 Hz, 1H); 13C NMR (CDCl3) δ -1.07, 17.36,
59.18, 84.44, 92.04, 121.08, 126.68, 129.86, 131.91, 134.82,
143.00; MS (CI) m/z 250 (M+, 22), 249 (M+ - 1, 100). Anal.
Calcd for C13H18OSSi: C, 62.35; H, 7.24. Found: C, 62.02; H,
7.09.
3-Iod o-4-(p h en yleth yn yl)th iop h en e (18). Thiophene 17c
(220 mg, 0.86 mmol) in THF-MeOH (3:1, 25 mL) under
nitrogen was cooled to 0 °C. Silver trifluoroacetate (380 mg,
1.72 mmol) was added, and the mixture was stirred for 5 min
to ensure complete dissolution. Then iodine (436 mg, 1.72
mmol) in THF-MeOH (3:1, 12 mL) was added dropwise, and
the reaction mixture was stirred at 0 °C for 4 h after the
addition was finished. The usual workup as described for 14
gave 18 (80 mg, 30%) as a colorless oil: 1H NMR (CDCl3) δ
7.36-7.41 (m, 3H), 7.44 (d, J ) 3.2 Hz, 1H), 7.48 (d, J ) 3.2
Hz, 1H), 7.59-7.63 (m, 2H); 13C NMR (CDCl3) δ 84.62, 84.70,
92.06, 122.87, 128.08, 128.32, 128.49, 128.58, 128.72, 131.64;
MS m/z 310 (M+, 100); high-resolution MS Calcd for C12H7SI
m/z 309.9311, found 309.9264.
1
colorless crystals: mp 50-52 °C; H NMR (CDCl3) δ 7.20 (d,
J ) 3.4 Hz, 1H), 7.39-7.49 (m, 5H), 7.54 (d, J ) 3.4 Hz, 1H);
13C NMR (CDCl3) δ 81.77, 122.46, 127.81, 128.10, 129.35,
129.89, 136.63, 145.49; MS m/z 286 (M+, 100); high-resolution
MS calcd for C10H7SI m/z 285.9314, found 285.9355.
3-P h en yl-4-[tr a n s-2′-(et h ylca r b on yl)vin yl]t h iop h en e
(22a ). A mixture of 21 (28.6 mg, 0.1 mmol), ethyl vinyl ketone
(33.6 mg, 0.4 mmol), Pd(OAc)2 (0.5 mg, 0.002 mmol), K2CO3
n
(34.5 mg, 0.25 mmol), and Bu4NI (36.9 mg, 0.1 mmol) in DMF
(3 mL) was stirred at 90 °C for 8 h under nitrogen. The
reaction mixture was diluted with ether (10 mL) and water
(10 mL). The ether layer was separated, and the aqueous layer
was extracted with ether (2 × 10 mL). The combined ether
solution was dried (MgSO4) and evaporated. The residue was
purified by column chromatography on silica gel (10 g, hex-
anes-EtOAc 4:1) to give 22a (12.1 mg, 50%) as a solid: mp
80-82 °C; 1H NMR (CDCl3) δ 1.03 (t, J ) 7.3, 7.3 Hz, 3H),
2.51 (q, J ) 7.3, 7.3, 7.3 Hz, 2H), 6.50 (d, J ) 16.2 Hz, 1H),
7.20 (d, J ) 3.2 Hz, 1H), 7.22-7.43 (m, 6H), 7.62 (dd, J ) 3.3,
0.6 Hz, 1H); 13C NMR (CDCl3) δ 8.22, 33.63, 124.08, 125.58,
127.17, 127.72, 128.62, 129.10, 135.49, 135.64, 135.81, 143.33,
200.83; MS m/z 242 (M+, 2). Anal. Calcd for C15H14OS: C,
74.34; H, 5.82. Found: C, 73.90; H, 5.67.
3-P h e n yl-4-[t r a n s-2′-(m e t h oxyca r b on yl)vin yl]t h io-
p h en e (22b). This was prepared from 21 (28.6 mg, 0.1 mmol)
and methyl acrylate (34.4 mg, 0.4 mmol) in the same manner
as described for 22a , yielding 22b (15 mg, 62%) as an oil: 1H
3-(Non yn -1′-yl)-4-(ph en yleth yn yl)th ioph en e (19a). This
was prepared by the reaction of 18 (62.0 mg, 0.2 mmol) and
1-nonyne (37.2 mg, 0.3 mmol) in acetonitrile (0.8 mL) and
triethylamine (2 mL) in the presence of Pd(PPh3)4 (23 mg, 0.02
mmol) and CuI (7.6 mg, 0.04 mmol) in the same manner as
described for 17a , yielding 19a (55.0 mg, 90%) as an oil: 1H
NMR (CDCl3) δ 0.87 (t, J ) 6.5, 7.0 Hz, 3H), 1.21-1.35 (m,
6H), 1.42-1.54 (m, 2H), 1.58-1.67 (m, 2H), 2.47 (t, J ) 6.9,
7.0 Hz, 2H), 7.33-7.39 (m, 4H), 7.54 (d, J ) 3.1 Hz, 1H), 7.52-
7.57 (m, 2H); 13C NMR (CDCl3) δ 13.97, 19.54, 22.60, 28.84,
31.66, 74.38, 83.60, 91.19, 92.88, 123.40, 125.09, 125.82,
126.95, 127.73, 128.22, 131.64; MS m/z 306 (M+, 19). Anal.
Calcd for C21H22S: C, 82.30; H, 7.24. Found: C, 82.61; H, 7.63.
3-(4′-H y d r o x y b u t y n -1′-y l)-4-(p h e n y le t h y n y l)t h io -
p h en e (19b). This was prepared by the reaction of 18 (37.0
mg, 0.12 mmol) and 3-butyn-1-ol (12.6 mg, 0.18 mmol) in
acetonitrile (0.5 mL) and triethylamine (1.25 mL) in the
presence of Pd(PPh3)4 (13.9 mg, 0.012 mmol) and CuI (4.6 mg,
0.024 mmol) in the same manner as described for 17a , yielding
19b (25.0 mg, 83%) as solids: mp 57-58 °C; 1H NMR (CDCl3)
δ 2.12 (br s, 1H), 2.73 (t, J ) 6.1, 6.1 Hz, 2H), 3.81 (t, J ) 5.4,
NMR (CDCl3
) δ 3.75 (s, 3H), 6.27 (d, J ) 16.0 Hz, 1H), 7.26
(d, J ) 3.2 Hz, 1H), 7.33-7.47 (m, 5H), 7.60 (d, J ) 16.0 Hz,
1H), 7.67 (d, J ) 3.2 Hz, 1H); 13C NMR (CDCl3) δ 51.48, 118.70,
124.03, 125.61, 127.67, 128.60, 129.08, 135.63, 138.02, 143.19,
167.28; MS m/z 244 (M
68.83; H, 4.95. Found: C, 68.48; H, 4.99.
+, 21). Anal. Calcd for C14H12O2S: C,
3-P h en yl-4-[tr a n s-2′-(m -n it r op h en yl)vin yl]t h iop h en e
(22c). A mixture of 21 (28.6 mg, 0.1 mmol), 3-nitrostyrene
(22.4 mg, 0.15 mmol), Pd(OAc)2 (2.2 mg, 0.01 mmol), and Ph3P
(5.2 mg, 0.02 mmol) in triethylamine (3 mL) and acetonitrile
(0.5 mL) was refluxed overnight under nitrogen. After removal
of the solvent, the residue was purified by chromatography
on silica gel (10 g, hexanes-EtOAc 8:1) to give 22c (20.0 mg,
65%) as an oil: 1H NMR (CDCl3) δ 6.97 (d, J ) 16.3 Hz, 1H),
7.12 (dd, J ) 16.3, 0.5 Hz, 1H), 7.28 (d, J ) 3.2 Hz, 1H), 7.39-
7.49 (m, 6H), 7.57 (dd, J ) 3.3, 0.5 Hz, 1H), 7.66-7.70 (m,
1H), 8.04-8.08 (m, 1H), 8.20-8.21 (t, J ) 2.0, 1.9 Hz, 1H);
13C NMR (CDCl3) δ 121.02, 121.89, 122.34, 123.82, 125.62,
127.35, 127.58, 128.61, 129.11, 129.47, 131.79, 136.23, 137.38,
139.43, 142.63, 148.93; MS m/z 307 (M+, 58). Anal. Calcd for

Applications of 3,4-Bis(trimethylsilyl)thiophene
J . Org. Chem., Vol. 62, No. 7, 1997 1951
C18H13O2NS: C, 70.34; H, 4.26; N, 4.56. Found: C, 70.32; H,
4.42; N, 4.29.
3.3 Hz, 1H), 7.13-7.21 (m, 5H), 7.45 (d, J ) 3.3 Hz, 1H); 13C
NMR (CDCl3) δ 20.56, 21.05, 122.75, 123.68, 126.70, 127.43,
128.12, 133.52, 136.58, 136.82, 137.07, 139.96, 142.08; MS m/z
278 (M+, 100). Anal. Calcd for C19H18S: C, 81.97; H, 6.52.
Found: C, 82.10; H, 6.52.
3-P h en yl-4-(n on yn -1′-yl)th iop h en e (23a ). This was pre-
pared by the reaction of 21 (33.0 mg, 0.12 mmol) and 1-nonyne
(21.5 mg, 0.17 mmol) in triethylamine (1.25 mL) and aceto-
nitrile (0.5 mL) in the presence of Pd(PPh3)4 (13.3 mg, 0.012
mmol) and CuI (4.4 mg, 0.023 mmol) in the same manner as
described for 17a , yielding 23a (23.5 mg, 73%) as a colorless
oil: 1H NMR (CDCl3) δ 0.88 (t, J ) 6.5, 6.8 Hz, 3H), 1.25-
1.40 (m, 8H), 1.51-1.56 (m, 2H), 2.34 (t, J ) 6.9, 7.0 Hz, 2H),
7.24 (d, J ) 3.3 Hz, 1H), 7.32-7.43 (m, 3H), 7.44 (d, J ) 3.3
Hz, 1H), 7.67-7.71 (m, 2H); 13C NMR (CDCl3) δ 14.01, 19.48,
22.60, 28.60, 28.85, 31.74, 75.77, 92.17, 121.82, 122.60, 127.29,
128.11, 128.20, 129.05, 135.72, 143.39; MS m/z 282 (M+, 4).
Anal. Calcd for C19H22S: C, 80.80; H, 7.85. Found: C, 80.69;
H, 8.10.
3-P h en yl-4-(4′-h ydr oxybu tyn -1′-yl)th ioph en e (23b). This
was prepared by the reaction of 21 (28.6 mg, 0.1 mmol) and
3-butyn-1-ol (10.5 mg, 0.15 mmol) in triethylamine (1.25 mL)
and acetonitrile (0.5 mL) in the presence of Pd(PPh3)4 (11.6
mg, 0.01 mmol) and CuI (3.8 mg, 0.02 mmol) in the same
manner as described for 17a , yielding 23b (22.8 mg, 100%) as
a colorless oil: 1H NMR (CDCl3) δ 1.78 (br s, 1H), 2.61 (t, J )
6.1, 6.1 Hz, 2H), 3.71 (t, J ) 6.1, 6.1 Hz, 2H), 7.25 (d, J ) 3.3
Hz, 1H), 7.34-7.45 (m, 3H), 7.49 (d, J ) 3.3 Hz, 1H), 7.63-
7.67 (m, 2H); 13C NMR (CDCl3) δ 23.95, 61.06, 77.85, 88.20,
122.05, 127.55, 128.19, 128.25, 129.61, 135.69, 143.58; MS m/z
228 (M+, 50). Anal. Calcd for C14H12OS: C, 73.65; H, 5.30.
Found: C, 73.21; H, 5.39.
3-P h en yl-4-(p-tolyl)th iop h en e (24a ). This was prepared
by the reaction of 21 (28.6 mg, 0.1 mmol) and p-tolylboronic
acid73 (13.6 mg, 0.1 mmol) in methanol-toluene (1:1, 4 mL)
in the presence of Pd(PPh3)4 (5.8 mg, 0.005 mmol) and 2 M
Na2CO3 (0.5 mL) in the same manner as described for 20,
yielding 24a (19 mg, 76%) as colorless crystals: mp 56-58 °C;
1H NMR (CDCl3) δ 2.32 (s, 3H), 7.06-7.07 (m, 4H), 7.17-7.30
(m, 7H); 13C NMR (CDCl3) δ 21.11, 123.58, 123.90, 126.81,
128.10, 128.87, 129.03, 133.70, 136.52, 136.77, 141.80; MS m/z
250 (M+, 100). Anal. Calcd for C17H14S: C, 81.56; H, 5.64.
Found: C, 81.12; H, 5.73.
3-P h en yl-4-(4′-m eth oxyp h en yl)th iop h en e (24b). This
was prepared by the reaction of 21 (28.6 mg, 0.1 mmol) and
4-methoxyphenylboronic acid73 (15.2 mg, 0.1 mmol) in metha-
nol-toluene (1:1, 4 mL) in the presence of Pd(PPh3)4 (5.8 mg,
0.005 mmol) and 2 M Na2CO3 (0.5 mL) in the same manner
as described for 20, yielding 24b (24.0 mg, 90%) as an oil: 1H
NMR (CDCl3) δ 3.78 (s, 3H), 6.77-7.13 (ABq, J ) 8.8 Hz, 4H),
7.17-7.27 (m, 6H), 7.29 (d, J ) 3.3 Hz, 1H); 13C NMR (CDCl3)
δ 55.21, 113.65, 123.16, 123.87, 126.82, 128.14, 129.05, 130.11,
136.81, 141.47, 141.79, 158.74; MS m/z 266 (M+, 100). Anal.
Calcd for C17H14OS: C, 76.66; H, 5.30. Found: C, 76.46; H,
5.32.
3-(Tr im eth ylsilyl)-4-h ep tylth iop h en e (25a ). To a solu-
tion of thiophene 17a (500 mg, 2 mmol) in hexanes (20 mL)
and triethylamine (4 mL) was added 10% Pd-C (0.11g, 0.1
mmol). The mixture was then stirred under a hydrogen
atmosphere for 24 h. The reaction mixture was filtered, and
the filtrate was collected. Removal of the solvent gave 25a
(507 mg, 100%) as a colorless oil: 1H NMR (CDCl3) δ 0.29 (s,
9H), 0.89 (t, J ) 6.9, 6.5 Hz, 3H), 1.25-1.38 (m, 8H), 1.57-
1.69 (m, 2H), 2.68 (dt, J ) 0.8, 8.1, 7.6 Hz, 2H), 7.00 (dt, J )
2.8, 0.8, 0.8 Hz, 1H), 7.36 (d, J ) 2.8 Hz, 1H); 13C NMR (CDCl3)
δ -0.15, 14.01, 22.63, 29.21, 29.63, 30.65, 31.00, 31.83, 120.68,
132.67, 141.02, 147.93; MS m/z 254 (M+, 77). Anal. Calcd for
C14H26SSi: C, 66.07; H, 10.30. Found: C, 66.37; H, 10.40.
3-(Tr im eth ylsilyl)-4-n on ylth iop h en e (25b). This was
prepared from 17b (556 mg, 2 mmol) in the same manner as
described for 25a , yielding 25b (562 mg, 100%) as a colorless
oil: 1H NMR (CDCl3) δ 0.30 (s, 9H), 0.90 (t, J ) 6.8, 6.4 Hz,
3H), 1.23-1.43 (m, 12H), 1.61-1.73 (m, 2H), 2.69 (dt, J ) 0.6,
8.2, 7.6 Hz, 2H), 7.01 (dt, J ) 2.8, 0.7, 0.7 Hz, 1H), 7.37 (d, J
) 2.8 Hz, 1H); 13C NMR (CDCl3) δ -0.15, 14.07, 22.66, 29.31,
29.57, 29.66, 30.63, 31.00, 31.91, 120.67, 132.67, 141.01,
147.92; MS m/z 282 (M+, 63). Anal. Calcd for C16H30SSi: C,
68.01; H, 10.70. Found: C, 68.26; H, 11.01.
3-(Tr im eth ylsilyl)-4-(ph en yleth yl)th ioph en e (25c). This
was prepared from 17c (1.28 g, 5 mmol) in the same manner
as described for 25a , yielding 25c (1.30 g, 100%) as a colorless
oil: 1H NMR (CDCl3) δ 0.29 (s, 9H), 3.00 (m, 4H), 7.04 (d, J )
2.7 Hz, 1H), 7.19-7.35 (m, 5H), 7.39 (d, J ) 2.7 Hz, 1H); 13C
NMR (CDCl3) δ -0.14, 32.67, 36.91, 121.32, 125.98, 128.34,
128.40, 132.86, 140.83, 141.77, 146.72; MS m/z 260 (M+, 73).
Anal. Calcd for C15H20SSi: C, 69.17; H, 7.74. Found: C, 69.19;
H, 7.76.
Gen er a l P r oced u r e for P r ep a r a tion of Bor oxin es 26a -
c. (a ) Tr is(4-h ep tylth ien -3-yl)bor oxin e (26a ). To a solu-
tion of 25a (50.8 mg, 0.2 mmol) in CH2Cl2 (8 mL) was added
a solution of BCl3 (1.0M) in CH2Cl2 (0.3 mL) under a nitrogen
atmosphere at -78 °C. The mixture was stirred for 2 h and
was allowed to slowly warm to 0 °C for 8 h. The reaction was
quenched with 0.5 M Na2CO3 solution (10 mL), and the
mixture was extracted with ether (3 × 15 mL). The organic
layer was dried (MgSO4), and the solvent was evaporated. The
crude product was chromatographed on silica gel (10 g,
hexanes-ether 1:1) to give 26a (26.5 mg, 64%) as a colorless
oil: 1H NMR (CDCl3) δ 0.88 (t, J ) 6.6, 6.3 Hz, 9H), 1.27-
1.44 (m, 24H), 1.69-1.77 (m, 6H), 3.08 (t, J ) 7.6, 7.4 Hz, 6H),
7.04 (d, J ) 3.0 Hz, 3H), 8.27 (d, J ) 3.0 Hz, 3H); MS m/z 624
(M+, 14); high-resolution MS Calcd for C33H51O3B3S3 m/z
624.3279, found 624.3326.
3-P h en yl-4-(n a p h t h -1′-yl)t h iop h en e (24c). This was
prepared by the reaction of 21 (28.6 mg, 0.1 mmol) and
1-naphthylboronic acid74 (17.2 mg, 0.1 mmol) in methanol-
toluene (1:1, 4 mL) in the presence of Pd(PPh3)4 (5.8 mg, 0.005
mmol) and 2 M Na2CO3 (0.5 mL) in the same manner as
described for 20, yielding 24c (22.2 mg, 78%) as colorless
(b) Tr is(4-n on ylth ien -3-yl)bor oxin e (26b). This was
prepared from 25b (67.5 mg, 0.24 mmol) and a solution of BCl3
(1.0 M) in CH2Cl2 (0.3 mL) to give 26b (38.0 mg, 67%) as a
colorless oil: 1H NMR (CDCl3) δ 0.88 (t, J ) 6.8, 6.4 Hz, 9H),
1.27-1.45 (m, 36H), 1.69-1.77 (m, 6H), 3.08 (t, J ) 7.6, 7.4
1
crystals: mp 104-106 °C; H NMR (CDCl3) δ 7.06-7.08 (m,
Hz, 6H), 7.04 (d, J ) 3.0 Hz, 3H), 8.27 (d, J ) 3.0 Hz, 3H); 13
C
5H), 7.25-7.43 (m, 5H), 7.46 (d, J ) 3.3 Hz, 1H), 7.73-7.84
(m, 3H); 13C NMR (CDCl3) δ 122.99, 125.19, 125.66, 125.88,
126.22, 126.68, 127.73, 127.99, 128.05, 128.15, 132.55, 133.68,
134.84, 136.40, 139.90, 143.15; MS m/z 286 (M+, 46). Anal.
Calcd for C20H14S: C, 83.88; H, 4.93. Found: C, 83.66; H, 4.92.
3-P h en yl-4-m esitylth iop h en e (24d ). This was prepared
by the reaction of 21 (28.6 mg, 0.1 mmol) and mesitylboronic
NMR (CDCl3) δ 14.04, 22.66, 29.34, 29.68, 30.65, 31.02, 31.92,
121.41, 141.28, 148.85; MS m/z 708 (M+, 13). Anal. Calcd for
C39H63O3B3S3: C, 66.11; H, 8.96. Found: C, 65.53; H, 8.84.
(c) Tr is[4-(p h en yleth yl)th ien -3-yl]bor oxin e (26c). This
was prepared from 25c (1.80 g, 6.92 mmol) and a solution of
BCl3 (1.0 M) in CH2Cl2 (10.5 mL) to give 26c (1.26 g, 85%) as
white solids: mp 119.5-120 °C; 1H NMR (CDCl3) δ 2.94-3.37
(AA′XX′, J ) 7.3, 7.3 Hz, 12H), 6.96 (d, J ) 3.0 Hz, 3H), 7.11-
7.26 (m, 15H), 8.08 (d, J ) 3.0 Hz, 3H); 13C NMR (CDCl3) δ
32.24, 37.51, 122.01, 125.94, 128.29, 128.64, 141.56, 141.77,
147.55; MS m/z 642 (M+, 8). Anal. Calcd for C36H33O3B3S3:
C, 67.32; H, 5.18. Found: C, 67.42; H, 5.04.
t
acid75 (18.0 mg, 0.11 mmol) in BuOH (4 mL) in the presence
t
of Pd(PPh3)4 (5.8 mg, 0.005 mmol) and BuOK (22.4 mg, 0.2
mmol) in a similar manner as described for 20, yielding 24d
(15.6 mg, 56%) as white crystals: mp 59-61 °C; 1H NMR
(CDCl3) δ 1.97 (s, 6H), 2.31 (s, 3H), 6.88 (s, 2H), 7.09 (d, J )
P r ep a r a tion of Th iop h en es 27a -j by th e Su zu k i Cou -
plin g Reaction . (a) 3-Heptyl-4-(ph en an th r -9′-yl)th ioph en e
(27a ). A mixture of 26a (41.6 mg, 0.067 mmol), 9-bro-
mophenanthrene (51.4 mg, 0.2 mmol), and Pd(PPh3)4 (23.1 mg,
0.02 mmol) in methanol-toluene (1:1, 6 mL) was stirred under
nitrogen. After 5 min, a 2 M Na2CO3 solution (1 mL) was
(73) Kabalka, G. W.; Sastry, U.; Sastry, K. A. R.; Knapp, F. F., J r.;
Srivastava, P.C. J . Organomet. Chem. 1983, 259, 269-274.
(74) Smith, K. Organometallic Compounds of Boron; Chapman and
Hall: London, 1985; p 118.
(75) Hawkins, R. T.; Lennarr, W. J .; Snyder, H. R. J . Am. Chem.
Soc. 1960, 82, 3053-3059.

1952 J . Org. Chem., Vol. 62, No. 7, 1997
Ye and Wong
added. The reaction mixture was then stirred while being
heated at reflux for 2 h at 110 °C. After addition of water (6
mL) and cooling to room temperature, the mixture was
extracted with ether (3 × 8 mL). The combined organic
solution was washed with water (6 mL), dried (MgSO4), and
concentrated. Purification by column chromatography on
silica gel (10 g, hexanes) yielded 27a (62.3 mg, 87%) as a
colorless oil: 1H NMR (CDCl3) δ 0.76 (t, J ) 7.0, 6.5 Hz, 3H),
1.06 (m, 8H), 1.40-1.45 (m, 2H), 2.29-2.39 (m, 2H), 7.13 (d,
J ) 3.2 Hz, 1H), 7.26 (d, J ) 3.3 Hz, 1H), 7.48-7.55 (m, 1H),
7.58-7.71 (m, 5H), 7.88 (dd, J ) 7.7, 1.7 Hz, 1H), 8.74 (t, J )
7.2, 7.8 Hz, 2H); 13C NMR (CDCl3) δ 13.93, 22.51, 28.89, 29.14,
29.83, 31.62, 120.43, 122.61, 122.79, 124.11, 126.49, 126.55,
126.63, 126.78, 127.02, 128.14, 128.61, 130.25, 130.49, 131.64,
132.07, 133.91, 141.25, 143.22; MS m/z 358 (M+, 100). Anal.
Calcd for C25H26S: C, 83.75; H, 7.31. Found: C, 83.86; H, 7.51.
(b ) 1,4-Bis(4′-h ep t ylt h ien -3′-yl)b en zen e (27b ) a n d 3-
Hep tyl-4-(4′-br om op h en yl)th iop h en e (27c). These were
prepared from boroxine 26a (41.6 mg, 0.067 mmol) and 1,4-
dibromobenzene (23.6 mg, 0.1 mmol) in the same manner as
described for 27a . Chromatography on silica gel (10 g,
hexanes) afforded 27b (9.0 mg, 21%) and 27c (16.5 mg, 49%).
afford 27g (99.0 mg, 98%) as a colorless oil: 1H NMR (CDCl3)
δ 0.04 (s, 9H), 0.86 (t, J ) 7.0, 6.4 Hz, 3H), 1.22-1.30 (m, 8H),
1.46-1.51 (m, 2H), 2.34 (t, J ) 8.1, 7.3 Hz, 2H), 6.97 (dt, J )
3.2, 0.8, 0.8 Hz, 1H), 7.08 (d, J ) 3.2 Hz, 1H), 7.15 (d, J ) 2.8
Hz, 1H), 7.47 (d, J ) 2.9 Hz, 1H); 13C NMR (CDCl3) δ -0.26,
14.01, 22.60, 29.04, 29.28, 29.38, 29.90, 31.73, 119.64, 123.72,
124.27, 132.54, 138.96, 142.10, 143.08; MS m/z 336 (M+, 63).
Anal. Calcd for C18H28S2Si: C, 64.23; H, 8.38. Found: C,
64.10; H, 8.52.
(f) 3-Non yl-4-[4′-(m eth oxyca r bon yl)ben zyl]th iop h en e
(27h ). This was prepared from boroxine 26b (94.4 mg, 0.133
mmol) and methyl 4-(bromomethyl)benzoate (91.6 mg, 0.4
mmol) to afford 27h (135.5 mg, 95%) as white crystals: mp
28-29 °C; 1H NMR (CDCl3) δ 0.88 (t, J ) 6.9, 6.3 Hz, 3H),
1.25 (m, 12H), 1.51-1.59 (m, 2H), 2.42 (t, J ) 7.9, 7.5 Hz, 2H),
3.90 (s, 3H), 3.94 (s, 2H), 6.80 (d, J ) 3.1 Hz, 1H), 6.94 (d, J
) 3.1 Hz, 1H), 7.22-7.98 (ABq, J ) 8.5 Hz, 4H); 13C NMR
(CDCl3) δ 14.01, 22.64, 28.85, 29.28, 29.48, 29.60, 31.87, 35.32,
51.89, 120.88, 122.59, 128.31, 128.76, 129.79, 139.22, 141.97,
145.72, 167.04; MS m/z 358 (M+, 26). Anal. Calcd for
C22H30O2S: C, 73.70; H, 8.43. Found: C, 73.62; H, 8.50.
(g) 3-Non yl-4-(tr a n s-2′-p h en ylvin yl)t h iop h en e (27i).
This was prepared from boroxine 26b (47.2 mg, 0.067 mmol)
and (E)-â-bromostyrene (36.6 mg, 0.2 mmol) to afford 27i (31.4
mg, 50%) as white crystals: mp 36.5-37 °C; 1H NMR (CDCl3)
δ 0.88 (t, J ) 6.9, 6.3 Hz, 3H), 1.27-1.41 (m, 12H), 1.56-1.70
(m, 2H), 2.67 (t, J ) 8.0, 7.5 Hz, 2H), 6.94 (d, J ) 3.1 Hz, 1H),
6.95 (d, J ) 16.2 Hz, 1H), 7.05 (d, J ) 16.2 Hz, 1H), 7.21-
7.51 (m, 6H); 13C NMR (CDCl3) δ 14.02, 22.66, 29.30, 29.47,
29.56, 29.98, 31.89, 120.40, 120.87, 121.88, 126.37, 127.43,
128.67, 129.52, 137.78, 138.84, 141.78; MS m/z 312 (M+, 100).
Anal. Calcd for C21H28S: C, 80.71; H, 9.03. Found: C, 80.99;
H, 9.07.
(h ) 3-(P h en ylet h yl)-4-(2′-m et h ylp r op en yl)t h iop h en e
(27j). This was prepared from boroxine 26c (128.4 mg, 0.2
mmol) and 1-bromo-2-methylpropene (81.0 mg, 0.6 mmol) to
afford 27j (131.0 mg, 90%) as an oil: 1H NMR (CDCl3) δ 1.83
(d, J ) 1.2 Hz, 3H), 1.89 (d, J ) 1.4 Hz, 3H), 2.81-2.94 (m,
4H), 6.03-6.05 (m, 1H), 6.89 (d, J ) 3.2 Hz, 1H), 7.01 (d, J )
3.0 Hz, 1H), 7.16-7.32 (m, 5H); 13C NMR (CDCl3) δ 19.63,
26.37, 31.29, 36.24, 118.67, 119.98, 121.89, 125.93, 128.35,
128.44, 136.40, 138.60, 141.44, 141.99; MS m/z 242 (M+, 74).
Anal. Calcd for C16H18S: C, 79.29; H, 7.49. Found: C, 79.42;
H, 7.57.
1
27b: white solid; mp 44-45 °C; H NMR (CDCl3) δ 0.85 (t, J
) 6.9, 6.4 Hz, 6H), 1.24-1.25 (m, 16H), 1.53-1.59 (m, 4H),
2.65 (t, J ) 8.0, 7.4 Hz, 4H), 7.05 (d, J ) 3.3 Hz, 2H), 7.21 (d,
J ) 3.2 Hz, 2H), 7.39 (s, 4H); 13C NMR (CDCl3) δ 14.04, 22.60,
29.04, 29.31, 29.36, 30.07, 31.74, 121.05, 122.96, 128.61,
136.05, 141.54, 142.72; MS m/z 438 (M+, 100). Anal. Calcd
for C28H38S2: C, 76.65; H, 8.73. Found: C, 76.93; H, 8.52.
1
27c: oil; H NMR (CDCl3) δ 0.86 (t, J ) 7.0, 6.4 Hz, 3H),
1.22 (m, 8H), 1.45-1.56 (m, 2H), 2.57 (dt, J ) 0.5, 8.0, 7.4 Hz,
2H), 7.03 (dt, J ) 3.3, 0.8, 0.8 Hz, 1H), 7.15 (d, J ) 3.2 Hz,
1H), 7.20-7.55 (AA′BB′, J ) 8.2, 4.5, 0.4 Hz, 4H); 13C NMR
(CDCl3) δ 14.05, 22.61, 29.01, 29.20, 29.32, 30.04, 31.74, 121.16,
121.35, 123.28, 130.40, 131.43, 136.35, 141.32, 141.76; MS m/z
336 (M+, 22), 338 (M+ + 2, 18). Anal. Calcd for C17H21SBr:
C, 60.53; H, 6.27. Found: C, 60.10; H, 6.43.
(c) 1,3,5-Tr is[(4′-h eptylth ien -3′-yl)m eth yl]ben zen e (27d).
This was prepared from boroxine 26a (62.4 mg, 0.1 mmol) and
1,3,5-tris(bromomethyl)benzene76 (35.7 mg, 0.1 mmol) to afford
27d (55.0 mg, 83%) as an oil: 1H NMR (CDCl3) δ 0.88 (t, J )
6.8, 6.4 Hz, 9H), 1.27 (m, 24H), 1.51-1.56 (m, 6H), 2.41 (t, J
) 8.0, 7.3 Hz, 6H), 3.80 (s, 6H), 6.71 (d, J ) 3.1 Hz, 3H), 6.84
(s, 3H), 6.90 (d, J ) 3.1 Hz, 3H); 13C NMR (CDCl3) δ 14.05,
22.65, 28.86, 29.17, 29.54, 31.83, 35.22, 120.41, 122.01, 127.26,
140.34, 140.40, 141.96; MS m/z 661 (M+ + 1, 9). Anal. Calcd
for C42H60S3: C, 76.30; H, 9.15. Found: C, 76.33; H, 9.28.
(d ) 4-Br om o-4′-h ep t yl-3,3′-b it h iop h en e (27e) a n d 3-
h ep tylth iop h en e (27f). These were prepared from boroxine
26a (41.6 mg, 0.067 mmol) and 3,4-dibromothiophene (24.2 mg,
0.1 mmol) in the same manner as described for 27a . Chro-
matography on silica gel (10 g, hexanes) afforded 27e (23.5
mg, 69%) and 27f (22.5 mg, 94%). 27e: colorless oil; 1H NMR
(CDCl3) δ 0.86 (t, J ) 6.9, 6.4 Hz, 3H), 1.22-1.25 (m, 8H),
1.43-1.55 (m, 2H), 2.48 (t, J ) 8.0, 7.4 Hz, 2H), 7.01 (d, J )
3.2 Hz, 1H), 7.16 (d, J ) 3.4 Hz, 1H), 7.20 (d, J ) 3.2 Hz, 1H),
7.32 (d, J ) 3.5 Hz, 1H); 13C NMR (CDCl3) δ 14.07, 22.61,
29.00, 29.12, 29.23, 29.77, 31.71, 112.90, 120.29, 123.00,
123.95, 124.99, 135.47, 137.52, 142.50; MS m/z 342 (M+, 26),
344 (M+ + 2, 23). Anal. Calcd for C15H19S2Br: C, 52.47; H,
5.58. Found: C, 52.98; H, 5.71.
4,4′-Bis(p h en yleth yl)-3,3′-bith iop h en e (28). A mixture
of 26c (107 mg, 0.167 mmol), 9,10-bis(bromomethyl)phenan-
threne78 (182 mg, 0.5 mmol), and Pd(PPh3)4 (58 mg, 0.05 mmol)
in methanol-toluene (1:1, 50 mL) was stirred for 5 min. After
that, 2 M Na2CO3 solution (5 mL) was added, and the reaction
mixture was further stirred and refluxed for 4 h. After
addition of water (40 mL) and cooling to room temperature,
the mixture was extracted with ether (3 × 30 mL). The
combined organic extracts were dried (MgSO4) and concen-
trated. Purification by silica gel chromatography (15 g,
hexanes) yielded 28 (42 mg, 44%) as colorless crystals: mp
1
59-61 °C; H NMR (CDCl3) δ 2.70-2.76 (m, 8H), 7.01-7.06
(m, 8H), 7.15-7.26 (m, 6H); 13C NMR (CDCl3) δ 31.26, 36.44,
120.81, 123.70, 125.88, 128.29, 128.34, 137.12, 141.46, 141.66;
MS m/z 374 (M+, 24). Anal. Calcd for C24H22S2: C, 76.96; H,
5.92. Found: C, 76.87; H, 6.06.
4,4′′′-Dih ep tyl-3,3′:4′,3′′:4′′,3′′′-qu a ter th iop h en e (29) a n d
4-Hep tyl-3,3′-bith iop h en e (30). To a solution of 27g (454
mg, 1.35 mmol) in CH2Cl2 (120 mL) was added a solution of
BCl3 (1.0 M) in CH2Cl2 (3 mL) under a nitrogen atmosphere
at -78 °C. Then the mixture was allowed to slowly warm to
room temperature and stirred for 24 h. The reaction was
quenched with 0.5M Na2CO3 solution (60 mL), and the mixture
was extracted with ether (3 × 100 mL). The combined ethereal
solution was dried (MgSO4), and the solvent was evaporated.
The residue was chromatographed on silica gel (25 g, hexanes-
ether 1:1) to give the corresponding boroxine intermediate,
which was reacted under self-coupling conditions as stated
above to afford 29 (73 mg, 21%) and 30 (39 mg, 11%). 29:
1
27f:77 colorless oil; H NMR (CDCl3) δ 0.88 (t, J ) 6.9, 6.5
Hz, 3H), 1.28-1.35 (m, 8H), 1.54-1.64 (m, 2H), 2.62 (t, J )
7.9, 7.4 Hz, 2H), 6.90-6.94 (m, 2H), 7.23 (dd, J ) 4.8, 2.9 Hz,
1H); 13C NMR (CDCl3) δ 14.05, 22.64, 29.13, 29.29, 30.28,
30.56, 31.81, 119.72, 124.97, 128.26, 143.23; MS m/z 182 (M+,
11). Anal. Calcd for C11H18S: C, 72.47; H, 9.95. Found: C,
72.68; H, 10.24.
(e) 4-(Tr im eth ylsilyl)-4′-h ep tyl-3,3′-bith iop h en e (27g).
This was prepared from boroxine 26a (62.4 mg, 0.1 mmol) and
4-iodo-3-(trimethylsilyl)thiophene (14) (84.6 mg, 0.3 mmol) to
1
(76) Borchardt, A.; Fuchicello, A.; Kilway, K. V.; Baldridge, K. K.;
Siegel, J . S. J . Am. Chem. Soc. 1992, 114, 1921-1923.
(77) This is a known compound. See: Roncali, J .; Garreau, R.;
Yassar, A.; Marque, P.; Garnier, F.; Lemaire, M. J . Phys. Chem. 1987,
91, 6706-6714.
colorless needle crystals; mp 62.5-64 °C; H NMR (CDCl3) δ
(78) Cheng, S. K. T.; Wong, H. N. C. Synth. Commun. 1990, 20,
3053-3061.

Applications of 3,4-Bis(trimethylsilyl)thiophene
J . Org. Chem., Vol. 62, No. 7, 1997 1953
0.86 (t, J ) 6.8, 5.6 Hz, 6H), 1.26-1.29 (m, 16H), 1.56-1.63
(m, 4H), 2.68 (t, J ) 8.0, 7.5 Hz, 4H), 7.02 (d, J ) 3.2 Hz, 2H),
7.12 (d, J ) 1.3 Hz, 2H), 7.26 (d, J ) 3.2 Hz, 2H), 7.27 (d, J )
0.9 Hz, 2H); 13C NMR (CDCl3) δ 14.12, 22.63, 29.10, 29.42,
29.55, 29.93, 31.77, 120.64, 121.15, 123.02, 124.91, 137.05,
138.11, 141.43; MS m/z 526 (M+, 2). Anal. Calcd for
C30H38S4: C, 68.39; H, 7.27. Found: C, 68.44; H, 7.47.
THF (5 mL) was added n-butyllithium (1.6 M in hexane, 0.8
mL, 1.28 mmol) at -78 °C under nitrogen. After the solution
was stirred for 0.5 h, a mixture of acetone (0.3 mL, 4.2 mmol)
and DMPU (0.12 mL) was added. After 1 h at -78 °C, it was
warmed to room temperature and quenched with saturated
aqueous ammonium chloride (5 mL). The resulting mixture
was extracted with ether (3 × 15 mL), and the ethereal
solution was dried (MgSO4). After removal of the solvent, the
residue was purified by column chromatography on silica gel
(20 g, hexanes-EtOAc 7:1) to give 36a (76 mg, 51%) as a
colorless solids: mp 65-66 °C; 1H NMR (CDCl3) δ 1.60 (s, 6H),
1.76 (br s, 1H), 2.94-3.17 (m, 4H), 7.00 (d, J ) 3.3 Hz, 1H),
7.08 (d, J ) 3.3 Hz, 1H), 7.16-7.31 (m, 5H); 13C NMR (CDCl3)
δ 30.97, 31.56, 36.92, 71.71, 120.11, 122.54, 125.90, 128.34,
128.41, 140.90, 141.94, 147.90; MS m/z 246 (M+, 1), 228 (M+
- H2O, 66). Anal. Calcd for C15H18OS: C, 73.13; H, 7.36.
Found: C, 73.33; H, 7.63.
1
30: colorless crystals; mp 36.5-37 °C; H NMR (CDCl3) δ
0.87 (t, J ) 6.9, 6.4 Hz, 3H), 1.25-1.27 (m, 8H), 1.55-1.60
(m, 2H), 2.65 (t, J ) 8.2, 7.2 Hz, 2H), 7.01 (d, J ) 3.2 Hz, 1H),
7.18 (dd, J ) 5.0, 1.3 Hz, 1H), 7.22 (d, J ) 3.4 Hz, 1H), 7.24
(dd, J ) 3.0, 1.3 Hz, 1H), 7.35 (dd, J ) 5.0, 3.0 Hz, 1H); 13C
NMR (CDCl3) δ 14.12, 22.62, 29.07, 29.42, 29.57, 29.84, 31.75,
120.96, 121.55, 122.74, 125.17, 128.22, 137.39, 141.52; MS m/z
264 (M+, 61). Anal. Calcd for C15H20S2: C, 68.13; H, 7.62.
Found: C, 68.31; H, 7.46.
3-(P h en yleth yl)-4-(tr i-n -bu tylsta n n yl)th iop h en e (31).
To a stirred solution of tri-n-butylstannyl chloride (1.3 g, 4
mmol) and Pd(PPh3)4 (231 mg, 0.2 mmol) in methanol-toluene
(1:1, 80 mL) was added 26c (428 mg, 0.67 mmol) and solid
sodium methoxide (216 mg, 4 mmol) under nitrogen. The
reaction mixture was refluxed for 24 h, cooled, and poured into
ice-water (50 mL). The resulting mixture was extracted with
ether (3 × 50 mL). The combined ethereal extract was dried
over MgSO4, and the solvent was removed. The residue was
purified by flash column chromatography on silica gel (40 g,
hexanes containing 1% Et3N) to give 31 (595 mg, 62%) as a
colorless oil: 1H NMR (CDCl3) δ 0.87 (t, J ) 7.2, 7.2 Hz, 9H),
1.07 (t, J ) 8.0, 8.3 Hz, 6H), 1.32 (sextet, J ) 7.1, 7.1, 7.1, 7.1,
7.1 Hz, 6H), 1.45-1.55 (m, 6H), 2.94-2.97 (m, 4H), 7.05 (d, J
) 2.6 Hz, 1H), 7.24 (d, J ) 2.6 Hz, 1H), 7.19-7.33 (m, 5H);
13C NMR (CDCl3) δ 10.20, 13.61, 27.31, 29.14, 33.88, 37.08,
120.16, 125.93, 128.36, 131.72, 140.02, 141.76, 147.67; ΜS (CI)
m/z 421 (M+ - C4H9, 100). Anal. Calcd for C24H38SSn: C,
60.39; H, 8.02. Found: C, 60.33; H, 8.16.
(b) 3-(P h en yleth yl)-4-for m ylth iop h en e (36b). Reaction
of 31 (286 mg, 0.6 mmol) in THF (5 mL) with n-butyllithium
(0.8 mL, 1.28 mmol), followed by addition of DMF (0.12 mL,
1.6 mmol) and DMPU (0.12 mL), gave, after chromatography
on silica gel (20 g, hexanes-EtOAc 10:1), 36b (76.5 mg, 59%)
as a white solid: mp 52-53 °C; 1H NMR (CDCl3) δ 2.88-3.24
(AA′XX′, J ) 7.3, 7.3 Hz, 4H), 6.92 (dd, J ) 3.0, 0.7 Hz, 1H),
7.16-7.31 (m, 5H), 8.08 (d, J ) 3.2 Hz, 1H), 9.97 (d, J ) 0.7
Hz, 1H); 13C NMR (CDCl3) δ 31.25, 36.31, 123.55, 125.94,
128.29, 128.50, 139.93, 140.28, 141.42, 141.75, 185.57; MS m/z
216 (M+, 76). Anal. Calcd for C13H12OS: C, 72.19; H, 5.59.
Found: C, 72.30; H, 5.42.
(c) 3-(P h en yleth yl)-4-(ph en ylselen en yl)th ioph en e (36c).
Reaction of 31 (143 mg, 0.3 mmol) in THF (2.5 mL) with
n-butyllithium (0.2 mL, 0.32 mmol), followed by addition of
phenylselenenyl bromide (70.8 mg, 0.3 mmol) and DMPU (0.06
mL), gave, after chromatography on silica gel (15 g, hexanes),
36c (55.6 mg, 54%) as a colorless oil: 1H NMR (CDCl3) δ 2.78-
2.94 (m, 4H), 7.00 (d, J ) 3.2 Hz, 1H), 7.08-7.28 (m, 10H),
7.48 (d, J ) 3.2 Hz, 1H); 13C NMR (CDCl3) δ 31.98, 36.39,
121.78, 123.88, 125.91, 126.43, 128.29, 128.43, 129.22, 130.18,
131.36, 132.49, 141.54, 144.03; MS m/z 344 (M+, 76). Anal.
Calcd for C18H16SSe: C, 62.97; H, 4.70. Found: C, 63.16; H,
4.81.
3-(P h en yleth yl)th iop h en e (32).79 Compound 31 (47.7 mg,
0.1 mmol) was destannylated by passing slowly through a
silica gel column (20 g, hexanes) to give 32 (18.5 mg, 98%) as
a colorless oil: 1H NMR (CDCl3) δ 2.92-2.94 (m, 4H), 6.91-
6.94 (m, 2H), 7.17-7.32 (m, 6H); 13C NMR (CDCl3) δ 32.16,
36.92, 120.31, 125.23, 125.95, 128.35, 128.40, 141.70, 142.11;
MS m/z 188 (M+, 65). Anal. Calcd for C12H12S: C, 76.55; H,
6.42. Found: C, 76.73; H, 6.48.
P h en yl[4-(tr im eth ylsilyl)th ien -3-yl]iod on iu m Tr ifla te
(38).80 To a stirred suspension of PhI(OAc)2 (3.3 g, 10.2 mmol)
in dry CH2Cl2 (50 mL) was added trifluoromethanesulfonic acid
(1.8 mL, 20.3 mmol) slowly at 0 °C with a syringe. The
mixture was stirred for 1 h at room temperature, during which
time the mixture became a clear yellowish solution. The
solution was then cooled to 0 °C, and 3,4-bis(trimethylsilyl)-
thiophene (1a ) (2.5 g, 11.0 mmol) in CH2Cl2 (25 mL) was added
dropwise with a syringe. After addition, the reaction mixture
was stirred at room temperature for 20 min. After evaporation
of the solvent, Et2O was added to crystallize the residue. The
solids formed were filtered, washed with Et2O, and dried in
3-(P h en yleth yl)-4-(ben zylca r bon yl)th iop h en e (33) a n d
Bis[4-(p h en yleth yl)th ien -3-yl]k eton e (34). A mixture of
31 (143.0 mg, 0.3 mmol), benzyl bromide (51.3 mg, 0.3 mmol),
and Pd(PPh3)4 (35.0 mg, 0.03 mmol) in THF (2 mL) was placed
in a sealed tube (14 × 1.25 cm2) under a carbon monoxide
atmosphere and then pressurized to 25-30 psi. The mixture
was stirred and heated at 50-60 °C for 2 days. The remaining
carbon monoxide was released, and the mixture was diluted
with ether (20 mL) and water (6 mL). The organic layer was
separated, and the water layer was extracted with ether (2 ×
6 mL). The combined organic layer was dried (MgSO4) and
evaporated. The residue was chromatographed on silica gel
(15 g, hexanes-EtOAc 15:1) to give 33 (46.0 mg, 50%) and 34
(16.0 mg, 13%). 33: colorless crystals; mp 57-58 °C; 1H NMR
(CDCl3) δ 2.81-3.21 (AA′XX′, J ) 7.3, 7.3 Hz, 4H), 4.17 (s,
2H), 6.83 (d, J ) 3.1 Hz, 1H), 7.14-7.35 (m, 10H), 8.07 (d, J
) 3.1 Hz, 1H); 13C NMR (CDCl3) δ 32.16, 36.27, 47.60, 122.83,
125.73, 126.85, 127.79, 128.16, 128.53, 128.63, 129.38, 134.71,
138.96, 141.79, 143.49, 193.10; MS m/z 306 (M+, 6). Anal.
Calcd for C20H18OS: C, 78.40; H, 5.92. Found: C, 77.92; H,
6.13.
1
vacuo to yield 38 (2.7 g, 53%): mp 169-172 °C (CHCl3); H
NMR (CDCl3) δ 0.28 (s, 9H), 7.43 (t, J ) 6.5, 6.5 Hz, 2H), 7.52
(dd, J ) 6.7, 1.1 Hz, 1H), 7.55 (d, J ) 2.9 Hz, 1H), 7.80 (d, J
) 6.4 Hz, 2H), 8.51 (d, J ) 2.9 Hz, 1H); 13C NMR (CDCl3) δ
-0.41, 100.82, 115.19, 131.99, 132.27, 132.98, 137.09, 140.86,
144.14; ΜS (CI) m/z 359 (M+ - OTf, 100). Anal. Calcd for
C14H16O3S2SiF3I: C, 33.08; H, 3.17. Found: C, 33.03; H, 2.90.
Gen er a l P r oced u r e for Tr a p p in g Rea ction s of 3,4-
Did eh yd r oth iop h en e (2). (a ) 4,9-Dih yd r o-4,9-o-ben zen o-
n a p h th o[2,3-c]th iop h en e (39a ) a n d 4,11-Dih yd r o-4,11-
eth en oa n th r a [2,3-c]th iop h en e (39b). To a mixture of 38
(254 mg, 0.5 mmol), 18-crown-6 (79 mg, 0.3 mmol), and
anthracene (89 mg, 0.5 mmol) in dry CH2Cl2 (6 mL) under N2
was added KF (87 mg, 1.5 mmol). The reaction mixture was
stirred for 30 min at room temperature. The resulting
precipitate was removed by filtration. The filtrate was evapo-
rated under reduced pressure, and the residue was chromato-
graphed on a silica gel column (8 g, hexanes) to give a mixture
of 39a and 39b (13 mg, 10%; 39a :39b ) 2.7:1 from 1H NMR)
as white solids: MS m/z 260 (M+, 100); high-resolution MS
34: colorless crystals; mp 69-71 °C; 1H NMR (CDCl3) δ
2.90-3.24 (AA′XX′, J ) 7.3, 7.3 Hz, 8H), 6.95 (d, J ) 3.1 Hz,
2H), 7.15-7.32 (m, 10H), 7.65 (d, J ) 3.2 Hz, 2H); 13C NMR
(CDCl3) δ 31.41, 36.63, 122.70, 125.82, 128.23, 128.52, 134.45,
140.97, 141.65, 143.05, 186.81; MS (CI) m/z 403 (M+ + 1, 100).
Anal. Calcd for C25H22OS2: C, 74.59; H, 5.51. Found: C,
74.75; H, 5.49.
Gen er a l P r oced u r e for P r ep a r a tion of 36a -c. (a )
3-(P h e n y le t h y l)-4-(1′-h y d r o x y -1′-m e t h y le t h y l)t h io -
p h en e (36a ). To a solution of 31 (286 mg, 0.6 mmol) in dry
(79) This is a known compound. See: Gronowitz, S.; Stenhammar,
K.; Svensson, L. Heterocycles 1981, 15, 947-959.
(80) Kitamura, T.; Matsuyuki, J .; Taniguchi, H. Synthesis 1994,
147-148.

1954 J . Org. Chem., Vol. 62, No. 7, 1997
Ye and Wong
calcd for C18H12S m/z 260.0654, found 260.0658. Anal. Calcd
for C18H12S: C, 83.04; H, 4.65. Found: C, 82.94; H, 4.92.
Careful partial recrystallization of the above mixture of 39a
and 39b from methanol provided a pure sample of 39a : mp
267-268 °C (lit.68 mp 268 °C); 1H NMR (CDCl3) δ 5.34 (s, 2H),
6.90 (s, 2H), 7.01-7.39 (AA′BB′, J ) 5.3, 3.3 Hz, 8H); 13C NMR
(CDCl3) δ 50.15, 114.38, 123.72, 125.46, 145.22, 147.02; MS
m/z 260 (M+, 100).
(f) 7-Oxabicyclo[2.2.1]h ept-5-en o-2,3-[c]th ioph en e (44a).
This was prepared by the reaction of 38 (254 mg, 0.5 mmol),
furan (1 mL), 18-crown-6 (79 mg, 0.3 mmol), and KF (87 mg,
1.5 mmol) in CH2Cl2 (5 mL). Chromatography on silica gel (8
g, hexanes-EtOAc 6:1) gave 44a (23 mg, 31%) as colorless
1
crystals: mp 70-72 °C; H NMR (CDCl3) δ 5.55 (t, J ) 0.9,
0.9 Hz, 2H), 6.73 (s, 2H), 6.92 (t, J ) 0.9, 0.9 Hz, 2H); 13C
NMR (CDCl3) δ 79.77, 112.08, 141.34, 151.38; MS m/z 150 (M+,
32). Anal. Calcd for C8H6OS: C, 63.98; H, 4.03. Found: C,
64.15; H, 4.14.
39b: 1H NMR (CDCl3) δ 5.11(t, J ) 3.3, 3.3 Hz, 2H), 6.84
(s, 2H), 7.01 (2H), 7.66 (s, 2H), 7.39-7.75 (AA′BB′, J ) 6.2,
3.3 Hz, 4H); 13C NMR (CDCl3) δ 46.34, 113.57, 121.20, 125.60,
127.45, 131.72, 138.93, 142.65, 147.31.
(g) 1-Meth yl-7-oxa bicyclo[2.2.1]h ep t-5-en o-2,3-[c]th io-
p h en e (44b). This was prepared by the reaction of 38 (508
mg, 1 mmol), 2-methylfuran (3 mL), 18-crown-6 (159 mg, 0.6
mmol), and KF (174 mg, 3 mmol) in CH2Cl2 (10 mL). Chro-
matography on silica gel (10 g, hexanes-EtOAc 5:1) gave 44b
(27.5 mg, 17%) as an oil: 1H NMR (CDCl3) δ 1.85 (s, 3H), 5.47
(d, J ) 1.7 Hz, 1H), 6.64 (dd, J ) 1.8, 0.7 Hz, 1H), 6.69 (d, J
) 1.8 Hz, 1H), 6.71 (d, J ) 5.5 Hz, 1H), 6.92 (dd, J ) 5.5, 1.7
Hz, 1H); 13C NMR (CDCl3) δ 15.77, 79.64, 87.82, 111.10,
111.93, 142.35, 144.30, 153.19, 154.48; MS m/z 164 (M+, 36).
Anal. Calcd for C9H8OS: C, 65.82; H, 4.91. Found: C, 65.63;
H, 4.90.
(h ) 1,4-Dim eth yl-7-oxa bicyclo[2.2.1]h ep t-5-en o-2,3-[c]-
th iop h en e (44c). This was prepared by the reaction of 38
(254 mg, 0.5 mmol), 2,5-dimethylfuran (1 mL), 18-crown-6 (79
mg, 0.3 mmol), and KF (87 mg, 1.5 mmol) in CH2Cl2 (5 mL).
Chromatography on silica gel (8 g, hexanes-EtOAc 6:1) gave
44c (11.5 mg, 13%) as an oil: 1H NMR (CDCl3) δ 1.82 (s, 6H),
6.61 (s, 2H), 6.72 (s, 2H); 13C NMR (CDCl3) δ 15.93, 87.56,
111.01, 145.31, 156.25; MS m/z 178 (M+, 11). Anal. Calcd for
C10H10OS: C, 67.38; H, 5.65. Found: C, 66.93; H, 5.76.
(b) 4,9-Dih ydr o-4,9-eth en on aph th o[2,3-c]th ioph en e (40).
This was prepared by the reaction of 38 (1.02 g, 2 mmol),
naphthalene (256 mg, 2 mmol), 18-crown-6 (317 mg, 1.2 mmol),
and KF (348 mg, 6 mmol) in CH2Cl2 (20 mL), yielding 40 (26
mg, 6%) as colorless crystals: mp 151-153 °C; 1H NMR
(CDCl3) δ 4.98 (dd, J ) 4.1, 3.1 Hz, 2H), 6.74 (s, 2H), 6.98 (dd,
J ) 4.3, 2.9 Hz, 2H), 6.97-7.27 (AA′BB′, J ) 5.2, 3.3 Hz, 4H);
13C NMR (CDCl3) δ 46.65, 113.00, 123.20, 124.84, 139.44,
145.87, 148.22; MS m/z 210 (M+, 78). Anal. Calcd for
C14H10S: C, 79.96; H, 4.79. Found: C, 79.69; H, 4.63.
(c) Th ien o[c]bicyclo[2.2.2]octa tr ien e (41). This was
prepared by the reaction of 38 (1.02 g, 2 mmol), benzene (8
mL), 18-crown-6 (317 mg, 1.2 mmol), and KF (348 mg, 6 mmol)
in CH2Cl2 (20 mL), yielding 41 (21 mg, 7%) as colorless
1
crystals: mp 65-66 °C; H NMR (CDCl3) δ 4.69 (tt, J ) 4.0,
4.0, 3.3, 3.3 Hz, 2H), 6.58 (s, 2H), 6.87 (dd, J ) 4.0, 3.3 Hz,
4H); 13C NMR (CDCl3) δ 43.94, 111.16, 139.40, 149.84; MS m/z
160 (M+, 100). Anal. Calcd for C10H8S: C, 74.96; H, 5.03.
Found: C, 74.91; H, 4.98.
(d) 3-Meth yl-3-(1′-m eth ylvin yl)cyclobu ten o[c]th ioph en e
(42a ) a n d 2-Meth yl-3-(3′-th ien ylm eth yl)-1,3-bu ta d ien e
(42b). These were prepared by the reaction of 38 (254 mg,
0.5 mmol), 2,3-dimethyl-1,3-butadiene (1.5 mL), 18-crown-6 (79
mg, 0.3 mmol), and KF (87 mg, 1.5 mmol) in CH2Cl2 (5 mL).
Chromatography on silica gel (8 g, n-pentane) gave a mixture
of 42a and 42b (22 mg, 27%; 42a :42b ) 1:1 from 1H NMR).
Careful chromatography on silica gel (n-pentane as eluent)
provided pure 42a and 42b.
(i) 4-(3′-Th ien oxy)bu ta n ol (46). This was prepared by the
reaction of 38 (508 mg, 1 mmol) and tetrabutylammonium
fluoride (1.0 M solution in THF, water content ∼5 wt %, 1.8
mL) in CH2Cl2 (10 mL). Chromatography on silica gel (10 g,
hexanes-EtOAc 3:1) gave 46 (10.0 mg, 6%) as a colorless oil:
1H NMR (CDCl3) δ 1.66 (br. s, 1H), 1.69-1.78 (m, 2H), 1.79-
1.91 (m, 2H), 3.72 (t, J ) 6.3, 6.1 Hz, 2H), 3.99 (t, J ) 6.1, 6.0
Hz, 2H), 6.24 (dd, J ) 3.2, 1.5 Hz, 1H), 6.74 (dd, J ) 5.2, 1.5
Hz, 1H), 7.17 (dd, J ) 5.2, 3.1 Hz, 1H); 13C NMR (CDCl3) δ
25.83, 29.51, 62.54, 70.07, 97.48, 119.43, 124.58, 157.84; MS
m/z 172 (M+, 9); high-resolution MS calcd for C8H12O2S m/z
172.0559, found 172.0557.
1
42a : colorless oil; H NMR (CDCl3) δ 1.51 (s, 3H), 1.83 (s,
3H), 2.66 and 3.09 (ABq, J ) 13.8 Hz, 2H), 4.79 (s, 1H), 4.88
(s, 1H), 6.85 (s, 1H), 6.89 (s, 1H); 13C NMR (CDCl3) δ 19.16,
25.45, 40.13, 52.19, 109.96, 113.94, 115.59, 138.19, 148.35,
149.84; MS m/z 164 (M+, 18); high-resolution MS calcd for
C10H12S m/z 164.0654, found 164.0615.
Ack n ow led gm en t. The financial support by a Re-
search Grants Council (Hong Kong) Earmarked Grant
for Research (CUHK77/93E) is gratefully acknowledged.
X.-S.Y. is on study leave from Department of Funda-
mental Courses, The Agricultural University of Central
China, Wuhan, China. We wish to thank Professor
Kazuo Achiwa, University of Shizuoka, J apan, for
providing experimental details concerning the genera-
tion of sulfur ylide 3.
1
42b: colorless oil; H NMR (CDCl3) δ 1.93 (s, 3H), 3.62 (s,
2H), 4.95 (s, 1H), 4.99 (s, 1H), 5.11 (s, 1H), 5.23 (s, 1H), 6.91-
6.95 (m, 2H), 7.22-7.25 (dd, J ) 5.1, 3.1 Hz, 1H); 13C NMR
(CDCl3) δ 21.07, 34.83, 113.48, 114.18, 121.00, 125.02, 128.52,
140.73, 142.38, 146.49; MS m/z 164 (M+, 27); high-resolution
MS calcd for C10H12S m/z 164.0654, found 164.0662.
(e) 3-Cya n ocyclobu ten o[c]th iop h en e (43). This was
prepared by the reaction of 38 (1.02 g, 2 mmol), acrylonitrile
(10 mL), 18-crown-6 (317 mg, 1.2 mmol), and KF (348 mg, 6
mmol) in CH2Cl2 (20 mL). Chromatography on silica gel (20
g, hexanes-EtOAc 5:1) yielded 43 (34 mg, 13%) as a colorless
oil: 1H NMR (CDCl3) δ 3.42-3.50 (ddd, J ) 14.0, 3.6, 1.0 Hz,
1H), 3.56-3.64 (ddd, J ) 14.0, 6.0, 1.0 Hz, 1H), 4.11-4.15 (ddd,
J ) 6.0, 3.6, 1.0 Hz, 1H), 6.94-6.96 (dt, J ) 1.2, 1.0, 1.0 Hz,
1H), 7.11-7.13 (dd, J ) 1.2, 1.0 Hz, 1H); 13C NMR (CDCl3) δ
25.60, 34.10, 116.98, 117.49, 118.93, 134.37, 138.11; MS m/z
135 (M+, 100). Anal. Calcd for C7H5NS: C, 62.19; H, 3.73;
N, 10.36. Found: C, 62.18; H, 3.58; N, 10.33.
1
Su p p or tin g In for m a tion Ava ila ble: Listing of H- and
13C-NMR spectra for compounds prepared (72 pages). This
material is contained in libraries on microfiche, immediately
follows this article in the microfilm version of the journal, and
can be ordered from the ACS; see any current masthead page
for ordering information.
J O962191N