A Convenient One-Pot Procedure to Arylcyclobutenes from Arylacetylenes

Full text of DOI:10.1021/jo990596c

8706
J . Org. Chem. 1999, 64, 8706-8708
Sch em e 1
A Con ven ien t On e-P ot P r oced u r e to
Ar ylcyclobu ten es fr om Ar yla cetylen es
Tamotsu Takahashi,*,†,‡ Baojian Shen,‡
Kiyohiko Nakajima,†,§ and Zhenfeng Xi†,|
Catalysis Research Center and Graduate School of
Pharmaceutical Sciences, Hokkaido University,
and CREST, Science and Technology Corporation (J ST),
Sapporo 060-0811, J apan, Department of Chemistry, Aichi
University of Education, Kariya, Aichi 448-8542, J apan,
and Department of Chemistry, Peking University,
Beijing 100871, China
reactions6 and CuCl-assisted new carbon-carbon bond
formation reactions7 of zirconacyclopentenes. In the
course of our further investigations, we found that an
intramolecular coupling between alkyl iodide and the
alkenylcopper moiety in 4 led to the formation of cy-
clobutene derivatives as shown in Scheme 1. And this
combination can provide a convenient one-pot procedure
from readily available arylacetylene and Cp2ZrEt2 to
arylcyclobutenes. Furthermore, the use of CuCl could
tolerate a wide variety of functional groups, and thus,
preparation of 1a would become easily available. Herein
we would like to report a convenient one-pot procedure
which affords 1a and various other 1,2-diarylcyclobutene
derivatives.
Received April 6, 1999
In tr od u ction
The design and synthesis of conjugated polymers or
oligomers with various repeat units are of great current
interest.1-3 Small rings such as cyclobutenes with a well-
defined skeleton have not been used as units or mono-
mers in conjugated polymers, to our knowledge. One
major reason is the limited number of convenient pre-
parative methods of conjugated cyclobutene derivatives
such as 1,2-diaryl cyclobutenes.4 Negishi et al.4d have
recently reported that 1,2-disubstituted cyclobutene de-
rivatives can be prepared from the reaction of tBuLi and
1,4-diiodo-1-alkenes which are isolated from treatment
of zirconacyclopentenes5 with I2. However, the use of
tBuLi does not tolerate other functional groups in the
starting diiodides. In fact, preparation of 1a by this
Resu lts a n d Discu ssion
We have reported that, when the substituent in the a
position of a zirconacyclopentene is an aryl group,
monoiodinolysis of the zirconacyclopentene gives only
monoalkyl iodide in high yield.6 As we expected, addition
of 1.2 equiv of I2 to the zirconacyclopentene of bis(4-
bromophenyl)acetylene, followed by addition of 1.2 equiv
of CuCl in a one-pot reaction, afforded a clean formation
of 1,2-bis(4-bromophenyl)cyclobutene (1a ) in 64% isolated
yield (eq 1, Table 1). The aryl bromides remained intact
method did not give a satisfactory result. On the other
hand, we have already reported selective halogenation
† CREST.
‡ Hokkaido University.
§ Aichi University.
| Peking University.
(1) Organic Materials for Non-Linear Optics II; Hann, R. A., Bloor,
D., Eds.; Redwood Press: Melksham, England, 1991.
(2) (a) Introduction to Molecular Electronics; Petty, M. C., Bryce,
M. R., Bloor, D., Eds.; Oxford University Press: New York, 1995. (b)
Tour, J . M. Chem. Rev. 1996, 96, 537.
during this reaction. Also, aryl chloride in 1b, aryl
bromide in 1c, and aryl iodide in 1d were all tolerated.
Symmetrically substituted cyclobutene and unsymmetri-
cally substituted cyclobutenes with aryl groups could be
readily prepared by this one-pot operation. In addition,
we found that the CuCl-mediated cyclization for cy-
clobutene formation could be a catalytic reaction. Addi-
(3) (a) Pearson, D. L.; Tour, J . M. J . Org. Chem. 1997, 62, 1376. (b)
J ones, L., II; Schumm, J . S.; Tour, J . M. J . Org. Chem. 1997, 62, 1388.
(4) (a) Houben-Weyl’s Methods of Organic Chemistry, Additional and
Supplementary Volumes to the 4th Edition; de Meijere, A., Ed; Georg
Thieme Verlag: Stuttgart, Germany, 1997; Col. E 17f, pp 615-826.
(b) Durst, T.; Breau, L. In Comprehensive Organic Synthesis; Trost,
B. M., Fleming, I., Eds.; Pergamon: Tokyo, 1991; Vol. 5, p 675. (c)
Negishi, E.; Liu, F.; Choueiry, D.; Mohamud, M. M.; Silveira, A., J r.;
Reeves, M. J . Org. Chem. 1996, 61, 8325. (d) Newman, M. S.; Kaugars,
G. J . Org. Chem. 1965, 30, 3295. (e) Fry, A. J .; Moore, R. H. J . Org.
Chem. 1968, 33, 425. (f) Hill, E. A.; Engel, M. R. J . Org. Chem. 1971,
36, 1356. (g) Photis, J . M.; Paquette, L. A. J . Am. Chem. Soc. 1974,
96, 4715. (h) Hill, E. A. J . Am. Chem. Soc. 1972, 94, 7462. (i) Snider,
B. B.; Rodini, D. J .; Conn, R. S. E.; Sealfon, S. J . Am. Chem. Soc. 1979,
101, 5283. (j) Reed, M. W.; Pollart, D. J .; Perri, S. T.; Foland, L. D.;
Moore, H. W. J . Org. Chem. 1988, 53, 2477. (k) Kasai, K.; Liu, Y.; Hara,
R.; Takahashi, T. Chem. Commun. 1998, 1989. (l) Liu, Y.; Sun, W.-H.;
Nakajima, K.; Takahashi, T. Chem. Commun. 1998, 1133. (m) Taka-
hashi, T.; Xi, Z.; Rischer, R.; Huo, S.; Xi, C.; Nakajima, K. J . Am. Chem.
Soc. 1997, 119, 4561.
(6) (a) Takahashi, T.; Aoyagi, K.; Hara, R.; Suzuki, N. J . Chem. Soc.,
Chem. Commun. 1993, 1042. (b) Takahashi, T.; Aoyagi, K.; Kondakov,
D. Y. J . Chem. Soc., Chem. Commun. 1994, 747. (c) Aoyagi, K.; Kasai,
K.; Kondakov, D. Y.; Hara, R.; Suzuki, N.; Takahashi, T. Inorg. Chim.
Acta 1994, 220, 319.
(7) (a) Takahashi, T.; Xi, Z.; Kotora, M.; Xi, C.; Nakajima, K.
Tetrahedron Lett. 1996, 37, 7521. (b) Kasai, K.; Kotora, M.; Suzuki,
N.; Takahashi, T. J . Chem. Soc., Chem. Commun. 1995, 109. (c)
Takahashi, T.; Kotora, M.; Kasai, K.; Suzuki, N. Tetrahedron Lett.
1994, 35, 5685. See also: (d) Takahashi, T.; Kotora, M.; Kasai, K.;
Suzuki, N.; Nakajima, K. Organometallics 1994, 13, 3, 4183. (e)
Takahashi, T.; Kotora, M.; Xi, Z. J . Chem. Soc., Chem. Commun. 1995,
361. (f) Takahashi, T.; Hara, R.; Nishihara, Y.; Kotora, M. J . Am. Chem.
Soc. 1996, 118, 5154.
(5) Takahashi, T.; Kageyama, M.; Denisov, V.; Hara, R.; Negishi,
E. Tetrahedron Lett. 1993, 34, 687.
10.1021/jo990596c CCC: $18.00 © 1999 American Chemical Society
Published on Web 10/21/1999

Notes
Ta ble 1. On e-P ot P r ep a r a tion of Ar ylcyclobu ten e
J . Org. Chem., Vol. 64, No. 23, 1999 8707
butene units (1q, 55%) could be readily obtained by
applying the known methods.11
Der iva tives via Zir con a cyclop en ten es
Exp er im en ta l Section 12
Rep r esen ta tive P r oced u r e for th e P r ep a r a tion of 1,2-
Disu bstitu ted Cyclobu ten es: Syn th esis of 1,2-Bis(4-br o-
m op h en yl)cyclobu ten e (1a ). To a solution of Cp2ZrCl2 (2.4
mmol, 700 mg) in THF (15 mL) was added ethylmagnesium
bromide (4.8 mmol, 5.05 mL, 0.95 mol/L THF solution) at -78
°C. After the solution was stirred for 1 h at -78 °C, 1,2-bis(4-
bromophenyl)acetylene (672 mg, 2.0 mmol) was added and the
reaction mixture was allowed to be warmed to 0 °C for 3 h. Iodine
(2.4 mmol, 609 mg) was then added at 0 °C, and the mixture
was stirred for an additional 3 h. Copper(I) chloride (2.4 mmol,
238 mg) was added, and the mixture was stirred at room
temperature for 6 h. The reaction mixture was then quenched
with 3 N HCl and extracted with hexane. The extract was
washed with water, NaHCO3 (20% aqueous solution), water,
NaS2O3, water, and brine and dried over MgSO4. Filtration and
evaporation provided a solid substance. Column chromatography
on silica gel with hexane as the eluent afforded 466 mg (64%,
purity > 98%) of the desired compound: mp 118.0-119.0 °C;
1H NMR (CDCl3, Me4Si) δ 7.44 (d, J ) 8.5 Hz, 4H), 7.34 (d, J )
8.5 Hz, 4H), 2.74 (s, 4H); 13C NMR (CDCl3, Me4Si) δ 138.20,
tion of 0.1 equiv of CuCl instead of 1.2 equiv of CuCl
afforded similar results. However, it required a longer
reaction time (24 h) or higher reaction temperature (50
°C, 6 h).
Bicyclic compound 1i was obtained in 62% isolated
yield from its corresponding bicyclic zirconacyclopentene.8
Bridged 1,2-disubstituted cyclobutenes 1j-m were also
134.62, 131.51, 127.52, 121.40, 26.80. Anal. Calcd for C16H12
-
Br2: C, 52.78; H, 3.32; Br, 43.89. Found: C, 52.44; H, 3.43; Br,
43.23. HRMS: calcd for C16H12Br2, 361.9305; found, 361.9311.
When a catalytic amount of CuCl (0.1 equiv) was used, the
reaction mixture was stirred for 24 h at room temperature or
for 6 h at 50 °C.
For preparation of bridged cyclobutenes 1j-m , the procedure
was essentially the same as the above. The ratio of the reagents
was as follows: 1.2 mmol of Cp2ZrCl2; 2.4 mmol of EtMgBr; 0.5
mmol of diyne; 1.2 mmol of I2; 1.2 mmol of CuCl.
easily prepared in good isolated yields (1j, 65%; 1k , 81%;
1l, 70%; 1m , 36%) starting from their corresponding
bridged zirconacyclopentenes.9 Trisubstituted cyclobutene
derivative 1n was obtained in 62% yield. Formation of
the bridged 1,2-disubstituted cyclobutene 1m has been
further verified by X-ray crystallography (see the Sup-
porting Information).10
As demonstrations using the halide-substituted cy-
clobutene derivatives as monomers, a variety of bridged
1,2-disubstituted cyclobutene derivatives containing two
cyclobutene units (1o, 72%; 1p , 31%) and three cyclo-
1-P h en yl-2-(2-th ien yl)cyclobu ten e (1e): 1H NMR (CDCl3,
Me4Si) δ 7.64-7.62 (m, 2H), 7.37-7.17 (m, 5H), 7.01-6.97 (m,
1H), 2.81-2.77 (m, 4H); 13C NMR (CDCl3, Me4Si) δ 136.54,
131.60, 131.40, 128.34, 128.31, 127.49, 127.08, 126.04, 125.13,
124.46, 27.53, 26.69. HRMS: calcd for C14H12S, 212.0659; found,
212.0656.
1,2-Dip h en ylcyclobu ten e (1f):13 mp 134.8-135.2 °C; 1H
NMR (CDCl3, Me4Si) δ 7.52 (d, J ) 7.2 Hz, 4H), 7.31 (t, J ) 7.2
Hz, 4H), 7.23 (t, J ) 7.2 Hz, 2H), 2.77 (s, 4H); 13C NMR (CDCl3,
(8) Negishi, E.; Cederbaum, F. E.; Takahashi, T. Tetrahedron Lett.
1986, 27, 2829.
(9) (a) Takahashi, T.; Xi, Z.; Nishihara, Y.; Huo, S.; Kasai, K.; Aoyagi,
K.; Denisov, V.; Negishi, E. Tetrahedron 1997, 53, 9123. (b) Takahashi,
T.; Kasai, K.; Xi, Z.; Denisov, V. Chem. Lett. 1995, 347.
(10) The X-ray data for 1m have been deposited in the Cambridge
Crystallographic Data Center: C26H22; fw ) 334.46; monoclinic space
group P21 (No. 4); a ) 10.0508(6), b ) 7.6936(5), c ) 11.861(1) Å; b )
92.197(6)°; V ) 916.5(1) Å3; R ) 0.047, Rw ) 0.055 based on 1860
observed reflections.
(11) King, A. O.; Negishi, E.; Villani, F. J .; Silveira, A. J . Org. Chem.
1978, 43, 358.
(12) For a general Experimental Section, see our recent paper:
Takahashi, T.; Xi, Z.; Yamazaki, A.; Liu, Y.; Nakajima, K.; Kotora, M.
J . Am. Chem. Soc. 1998, 120, 1672-1680.
(13) (a) Newman, M. S.; Kaugars, G. J . Org. Chem. 1965, 30, 3295.
(b) Dodson, R. M.; Zielske, A. G. J . Org. Chem. 1967, 32, 28. (c)
McMurry, J . E.; Kees, K. L. J . Org. Chem. 1977, 42, 2655.

8708 J . Org. Chem., Vol. 64, No. 23, 1999
Notes
Me4Si) δ 138.74, 136.20, 128.29, 127.45, 126.06, 26.79. HRMS:
calcd for C16H14, 206.1095; found, 206.1096.
mmol, 521 mg) was added and the mixture was stirred for 3 h
at 50 °C. After this, iodine (2.4 mmol, 609 mg) was added at
-78 °C and the mixture was warmed to room temperature and
stirred for 1 h. Finally copper(I) chloride (2.4 mmol, 238 mg)
was added and the mixture was stirred at 50 °C for 1 h. The
reaction mixture was quenched with water and extracted with
ether. The organic phase was washed with water, NaHCO3 (20%
aqueous solution), water, NaS2O3 (saturated aqueous solution),
water, and brine, and dried over MgSO4. Filtration, evaporation,
and column chromatography on silica gel (1:1 hexane/Et2O, v/v)
afforded 349 mg (62%) of the desired compound (pale yellow oily
substance): 1H NMR (CDCl3, Me4Si) δ 7.58-7.49 (m, 4H), 7.37-
7.21 (m, 6H), 2.92-2.87 (m, 1H), 2.81-2.79 (m, 1H), 2.71-2.67
(m, 1H); 13C NMR (CDCl3, Me4Si) δ 141.19, 136.88, 136.53,
135.90, 128.32 (2C), 128.26 (2C), 127.51, 127.14, 126.58 (2C),
125.54 (2C), 31.55, 27.59, -1.54, -1.85. HRMS: calcd for
C18H20OSi, 280.1282; found, 280.1286.
1-Octyl-2-ph en ylcyclobu ten e (1g): 1H NMR (CDCl3, Me4Si)
δ 7.38-7.19 (m, 5H), 2.67-2.65 (m, 2H), 2.49-2.42 (m, 4H),
1.59-1.53 (m, 2H), 1.42-1.32 (m, 14H), 0.96-0.93 (t, J ) 7 Hz,
3H); 13C NMR (CDCl3, Me4Si) δ 143.58, 137.04, 136.34, 128.22,
126.28, 125.54, 31.96, 30.13, 29.79, 29.67, 29.60, 29.38, 27.60,
27.30, 25.75, 22.72, 14.09. HRMS: calcd for C20H30, 270.2346;
found, 270.2345.
1-Bu tyl-2-(1-n a p h th yl)cyclobu ten e (1h ): 1H NMR (CDCl3,
Me4Si) δ 8.35-8.33 (d, J ) 8 Hz, 1H) 7.95-7.83 (m, 2H), 7.59-
7.52 (m, 4H), 3.07-3.06 (m, 2H), 2.73-2.71 (m, 2H), 2.37 (m,
2H), 1.62-1.45 (m, 4H), 1.03-0.99 (t, J ) 7.5 Hz, 3H); 13C NMR
(CDCl3, Me4Si) δ 145.65, 137.54, 134.56, 133.85, 131.23, 128.27,
126.99, 125.98, 125.54, 125.47, 125.32, 125.23, 30.18, 29.74,
29.46, 28.18, 22.74, 13.91. HRMS: calcd for C18H20, 236.1564;
found, 236.1569.
7-P h en ylbicyclo[4.2.0]oct-6(7)-en e (1i): 1H NMR (CDCl3,
Me4Si) δ 7.34-7.15 (m, 5H), 2.83-2.76 (m, 2H), 2.45-2.31 (m,
2H), 2.19-2.07 (m, 2H), 1.91-1.75 (m, 2H), 1.41-1.27 (m, 2H),
1.18-1.12 (m, 1H); 13C NMR (CDCl3, Me4Si) δ 146.65, 136.58,
131.83, 128.22, 126.20, 125.41, 37.66, 34.41, 33.20, 27.22, 26.78,
25.03. HRMS: calcd for C14H16, 184.1251; found, 184.1269.
1,3-Bis(2-ph en ylcyclobu ten yl)bu tan e (1j): 1H NMR (CDCl3,
Me4Si) δ 7.32-7.14 (m, 10H), 2.61-2.59 (m, 4H), 2.43-2.42 (m,
8H), 1.61-1.58 (m, 4H); 13C NMR (CDCl3, Me4Si) δ 143.21,
137.28, 136.23, 128.27, 126.36, 125.54, 29.92, 27.60, 27.28, 25.78.
HRMS: calcd for C24H26, 314.2033; found, 314.2031.
Rep r esen ta tive P r oced u r e for th e P r ep a r a tion of 1o-
p : Syn th esis of 1,1′-Bis(2-p h en ylcyclobu ten yl)-4,4′-bip h en -
yl (1o). To a THF solution of 1-(4-bromophenyl)-2-phenylcy-
clobutene (1c) (2.0 mmol), prepared and isolated as described
above, was added n-BuLi (2 mmol), and the mixture was stirred
at 0 °C for 1 h. After addition of flame-dried zinc chloride (3.0
mmol), to the reaction mixture was added 1-(4-bromophenyl)-
2-phenylcyclobutene (1c) (2.0 mmol) and a catalytic amount of
Pd(PPh3)4 (0.1 mmol) at room temperature.11 After being heated
to 50 °C and stirred for 6 h, the reaction mixture was quenched
with 3 N HCl and extracted with Et2O. The extract was washed
with water, NaHCO3 (20% aqueous solution), water, NaS2O3,
water, and brine, and dried over MgSO4. Filtration and evapora-
tion provided a solid substance. Column chromatography on
silica gel with hexane as the eluent afforded 592 mg (72%
isolated yield, purity > 98%) of the desired compound: mp
180.5-182.5 °C (decomp); 1H NMR (CDCl3, Me4Si) δ 7.61-7.23
(m, 18H), 2.81 (s, 8H); 13C NMR (CDCl3, Me4Si) δ 139.66, 139.12,
138.34, 136.27, 135.21, 128.35, 127.52, 126.72, 126.52, 126.14,
26.94, 26.78. HRMS: calcd for C32H26, 410.2033; found, 410.2044.
1,4-Bis(2-p h en ylcyclob u t en yl)p en t a n e (1k ): 1H NMR
(CDCl3, Me4Si) δ 7.45-7.11 (m, 10H), 2.57-2.13 (m, 10H), 1.69-
1.29 (m, 8H); 13C NMR (CDCl3, Me4Si) δ 143.44, 137.13, 136.27,
128.27, 126.34, 125.54, 30.02, 29.77, 27.60, 27.15, 25.77.
HRMS: calcd for C25H28, 328.2190; found, 328.2181.
1,4-Bis(2-bu tylcyclobu ten yl)ben zen e (1l): 1H NMR (CDCl3,
Me4Si) δ 7.26 (m, 4H), 2.59-2.36 (m, 12H), 1.52-1.35 (m, 8H),
0.94-0.90 (t, J ) 7.5 Hz, 6H); 13C NMR (CDCl3, Me4Si) δ 143.35,
136.96, 134.40, 125.47, 29.92, 29.49, 27.68, 25.73, 22.83, 13.99.
HRMS: calcd for C22H30, 294.2346; found, 294.2355.
Ack n ow led gm en t. We thank the Ministry of Edu-
cation, Science, Sports, and Culture of J apan for the
support of this study.
1,4-Bis(2-p h en ylcyclobu ten yl)ben zen e (1m ): mp 158.4-
1
159.0 °C; H NMR (CDCl3, Me4Si) δ 7.53-7.48 (m, 8H), 7.33-
7.21 (m, 6H), 2.76 (s, 8H); 13C NMR (CDCl3, Me4Si) δ 138.98,
138.46, 136.27, 135.22, 128.30, 127.46, 126.13, 125.93, 26.89,
26.65. Anal. Calcd for C26H22: C, 93.37; H, 6.63. Found: C, 93.44;
H, 6.64. HRMS: calcd for C26H22, 334.1720; found, 334.1717.
Syn th esis of 1,2-Dip h en yl-3-(h yd r oxyd im eth ylsilyl)cy-
clobu ten e (1n ). To a solution of Cp2ZrCl2 (701 mg, 2.4 mmol)
in THF (10 mL) was added ethylmagnesium bromide (4.8 mmol,
4.706 mL, 1.02 mol/L THF solution) at -78 °C. After the solution
was stirred for 1 h at -78 °C, diphenylacetylene (356 mg, 2.0
mmol) was added. And then the reaction mixture was warmed
to 0 °C and stirred for 3 h. Then ethoxydimethylvinylsilane (4.0
Su p p or tin g In for m a tion Ava ila ble: Text providing char-
acterization data for 1b-d ,p ,q and experimental details for
the X-ray analysis of 1m , an X-ray structure of 1m , tables of
crystallographic data, positional and thermal parameters, and
1
bond lengths and angles for 1m , and H and 13C NMR spectra
of 1a -q (26 pages). This material is available free of charge
via the Internet at http://pubs.acs.org.
J O990596C