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Azo-Dye Rotaxanes.

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mlzFigure 2. Positive FAB-MS spectrum of catenane 13 in a p-nitrobenzyl alcohol
matrix (display from m / i = 200 to 1400; peaks at m / r = 307.1 and 460.1 result from
thealcoholmatrix). The peak at mji = 1185.4correspondstolcatenane - H i ] , and
at m/z = 593.2 to [macrocycle - H']. The absence of peaks between the molecular
ion peak and the the peak corresponding to the individual macrocycle is characteristic for catenated species [16].
Experimental Section
General procedure for ruthenium benzylidene catalyzed RCM : Under exclusion
from air and moisture, 1 (5 mol%) in CH,CI, was added to a 0.01 M solution of the
diolefin (typically 200 to 900 mg) in CH,CI,. After the mixture was stirred for 6 h
at room temperature, additional catalyst (5 mol%) was added, and stirring continued for 6 h. The solvent was then removed under reduced pressure, and the crude
reaction mixture purified by repeated column chromatography (silica gel, CH,CI,/
MeOH 9614 viv) to yield the [2]catenates as burgundy solids. All compounds were
characterized by NMR spectrscopy, FAB-MS, and elemental analysis.
Received: December 23, 1996 [Z9924IE]
German version: Angew. Chem. 1997, 109, 1365-1367
Keywords: catenanes
template synthesis
- ruthenium .
[l] Recent reviews on catenanes and related compounds: a) J.-P. Sauvage, C. 0.
Dietrich-Buchecker, J.-C. Chambron in Comprehensive Supramolecular Chem. h) special
rsrry, Vol. Y (Ed.: L-M. Lehn), Pergamon Press, Oxford, 1 9 9 6 , ~43;
issue of the New J. Chem. (Ed.: J.-P. Sauvage) 1993, 1 7 ; c) D. B. Amabilino,
J. F. Stoddart, Chem. Rev. 1995, 95, 2725; d j D. P. Philip, J. F. Stoddart,
Angew. Chem. 1996, 108, 1242; Angew. Chem. Inf. Ed. Engl. 1996,35, 1154.
[2] a) A.D. Bates, A. Maxwell, D N A Topology, Oxford University Press, New
York, 1993; b) S. D. Levene, C. Donahue, T. C. Boles, N. R. Cozzarelli, Biophys. J 1995,69, 1036.
[3] a) E.J. Wasserman, J Am. Chem. Soc. 1960,82,4433; b) H. L. Frisch, E. J.
Wasserman, &id. 1960,82,4433;c) G. Schill, Cutenanes, Rotaxunes andKnois,
Academic Press, New York, 1971.
141 a) C.0.Dietrich-Buchecker, J.-P. Sauvage, Tetrahedron Lerf. 1983, 24, 5091 ;
b) C. 0. Dietrich-Buchecker, J.-P. Sauvage, Bioorganic Chemistry Frontiers,
Vol. 2, Springer, Berlin, 1991, pp. 195-248.
IS] Catenanes whose rings incorporate transition metal atoms: M. Fujita, K.
Ogura, Coord. Chem. Rev. 1996, 148,249.
[6] a ) J. Y Ortholand, A. M. Z. Slawin, N. Spencer, J. F. Stoddart, D. J. Williams,
Angew. Chem. 1989, 101, 1404; Angew. Chem. l n i . Ed. Engl. 1989, 28, 1394;
h) D. B. Amabilino, P.-L. Anelli, P. R. Aston, G. R. Brown, E. Cordova,
L. A. Godinez, W. Hayes, A. E. Kaifer, D. Philip, A. M. Z. Slawin, N. Spencer,
M. S . Tolley, D. J. Williams, F. J. Stoddart, J. Am. Chem. Soc. 1995, 117,11 142.
[7] a) F. Vogtle, S. Meier, R. Hoss, Angew. Chem. 1992, 104, 1628; Angew. Chem.
h r . Ed. Engl. 1992, 3f, 1619; b) F. Vogtle, T. Dunnwald, T. Schmldt, Acc.
Chem. Res. 1996,29,451, c) C.A. Hunter. J Am. Chem. Soc. 1992,114,5303;
d) A. G. Johnston, D. A. Leigh, R. I. Pritchard, M. D. Deegan, Angew. Chem.
1995, 107. 1324; Angew. Chem. fnt. Ed. Engl. 1995,34, 1209.
IS] Recent reviews on RCM: a) R. H. Grubbs, S J Miller, G. C. Fu, A m . Chem.
Res. 1995,28,446;
bl H.-G. Schmalz, Angeu,. Chem. 1995,107, 1981; Angew.
Chem. fnr. Ed. Enal
- 1995.34. -i m- - z[9J Early attempts to synthesrze catenanes with RCM: a) R. Wolovsky, J Am.
Chem. SOC.1970, 92, 2132; b) D.A. Ben-Efraim, C. Batich, E. Wasserman,
ibid. 1970. 92. 2133
[lo] P. Schwab, R. H.-Grrrbbs, J. W. Zrller, J. h 7 . Chem. Soc. 1996, 118, 100
[fll a) G. C. Fu. R. H. Grubbs, J Am. Chem. SOC.1992, 114, 5426; b j M. D. E.
Forbes, J. T. Patton, T. L Myers, H. D. Maynard, D. W. Smith, G . R. Schulz.
K. B. Wagener, hid. 1992, l f 4 , 10978, c) S . J. Miller, S. H Kim, Z. R. Chen,
R.H. Grubbs, ibid. 1995, lf7, 2108.
1121 a) S . I. Miller, H. E. Blackwell, R. H. Grubbs, J Am. Chem. Soc. 1996, If&
9606; b) A. Fiirstner. K. Langemann, J. Org. Chem. 1996. 61, 3942; c) T. D.
Clark, M. R. Ghadlri, J Am. Chem. Soc. 1995, 117, 12364; d) 8 . Konig, C.
Horn, Synkir 1996, 1013; e) A. Firstner, N. Kindler, Tetrahedron Lerr 19%.
37. 7005; f) P. Bertinato, E. J. Sorensen, D. Meng, S. J. Danishefsky. J. Org.
Chem. 1996,61,8000;g) Z.Xu,C. H. Johannes, S . S. Salman, A. H. Hoveyda,
J Am. Chem. SOC.1996,118,10926; h) K.C.Nicolaou, Y. He, D. Vourloumis,
H. Vallberg, Z. Yang, Angew. Chem. 1996, 108, 2554, Angew. Chem. In[. Ed.
Engl. 1996, 35, 2399.
[I 31 Macrocycle 2 was prepared as described: C. Dietrich-Buchecker, J.-P. Sauvage,
Terrahedrori 1990,46,503; acyclic ligands 3 and 4 were prepared from dpp with
2-(2-~hloroethoxy)ethanoI/Na,CO,and 2-[2-(2-chloroethoxy)ethoxy]ethanol/
Na,CO,, respectively, in N,N-dimethylformamide (DMF) and subsequent
alkylation with allylbromide1NaH In DMF.
[14] M. J. Marsella, H. D. Maynard, R. H. Grubbs. Angew. Chem. 1997,10Y, 1147;
Angew. Chem. I n f . Ed. Engl. 1997, 36, 1101
1151 a) G . R.Desiraju, Angen,. Chem. 1995,107,2541; Angew Chem. In/. Ed. Engl.
1995,34,2311; b) for a comprehensive survey on K-donor/n-acceptor interactions in related supramolecnlar assemblies see also ref. [Id].
[16j These interactions have been observed in the solid state for a structurally
related [2]catenate: a) M. Cesario, C. 0. Dietrich-Buchecker, G. Guilhelm, C.
Pascard. J:P. Sauvage. J Chem. Soc. Chem. Commun. 1985, 244; bj C. 0.
Dietrich-Buchecker, G. Guilhelm, L-M. Kern, C. Pascard, .I.-P. Sauvage, Inorg.
Chem. 1994. 33, 3498.
1171 C. 0.Dietrich-Buchecker, E. Leize, J.-F. Nlerengarten, J . 4 . Sauvage, A. Van
Dorsselar, J Chem. SOC.Chem. Commun. 1994, 2257. and references therein.
Azo-Dye Rotaxanes
Sally Anderson,* Tim
Azo dyes are the largest and most commercially important
class of synthetic colorants.['l Their interaction with cyclodextrins (CDs) has been investigated as a method of controlling
their stability, solubility, and aggregation.['' Rotaxane formation offers a way o f converting these labile inclusion complexes
into robust encapsulated chromophores, with the dye permanently protected inside the cavity of the CD. There seem to
be no previous reports of rotaxanes of this type.131 We have
synthesized a range of water-soluble azo-dye rotaxanes
using the hydrophobic effect to direct rotaxane formation
(Scheme 1).*41
When azobenzene diazonium salt l a is added to an aqueous
solution of p-naphthol 2 in the presence of either a-CD 3a or
p-CD 3b at 0-5 "C, the solution immediately turns deep purple.
Paper chromatography reveals the formation of the fast-running rotaxanes 4a c 3a or 4a c3b, respectively, as well as the less
mobile non-rotaxanated dye 4a, which is rather insoluble in
water and can be separated from the rotaxanes by centrifugation. Rotaxanes 4a c 3a and 4a c 3b were purified by paper chromatography and recrystallization, and isolated in 12 and 15%
yields, respectively. The tolidine diazonium salt lb also gave a
[*] Dr. S. Anderson, Dr. H. L. Anderson, Dr. T. D. W. Claridge
University of Oxford
Dyson Perrins Laboratory
South Parks Road, Oxford OX1 3QY (UK)
Fax: Int. code +(1865)275-674
0 VCH Verlagsgesellschuft mbH, 0-69451 Weinheim, 1997
D. W. Claridge, and
Harry L. Anderson*
This work was supported by the Engineering and Physical Sciences Research
Council and an Award to Newly Appointed Science Lecturers from the
Nuffield Foundation. S. A. gratefully acknowledges a Research FeIlowship
and generous support from Trinity College, Cambridge (UK).
0570-083319713612-1310$17.50 f .SO10
Angew. Chem Int. Ed. Engl. 1997,36, No. 12
l a @ =l , R = H )
1 b ( n = 0, R
3a(n=l) 3b(n=2)
rotaxane with 3b when allowed to react with 2 under similar
conditions, but it failed to give any rotaxane with 3a.
Diazonium salt l b is evidently too large to bind in the cavity of
3a. Rotaxane 4 b c 3 b was isolated in 6 % yield.
All three rotaxanes were fully characterized by * H and 13C
NMR spectroscopy and ESI-MS (Table l).[51In all mass spectra
the most abundant molecular ion corresponds to the tetraanion
formed by loss of four sodium cations. The NMR spectra show
that the symmetry of the CD is imposed on the azo dye, making
its two ends nonequivalent, whereas the symmetry of the CD is
maintained, since it rotates rapidly around its guest on the
NMR timescale. When 'HNMR spectra are recorded in
[DJDMSO, all the signals for hydroxyl groups are sharp and
well-resolved. Two signals appear at about 6 = I 7 due to the
hydrogen-bonded phenolic OH groups at each end of the rotaxanes. The 'H NMR spectrum of 4 b c 3 b was assigned by I-DNOESY and 2-D-COSY NMR techniques. Long-range weak
NOES are observed with 1-D double-pulsed field-gradient spinecho (DPFGSE) NOESY experiments.r61A separate and complementary set of NOEs is seen from each rim of the CD
(Scheme 2). For example, the naphthalene proton HA shows
NOEs to hydroxyi protons OH-2 and OH-3 as well as to the
proximate internal CD proton H-3, whereas HAshows NOEs to
OH-6 and H-6, which are situated on the opposite rim of the
CD. Both protons H,. and H, show NOEs to CD H-5 and H-3
on the inner surface of the CD. This shows that the central
portion of the dye is encapsulated by the CD.
Angrn. Chrm. In1 Ed. Engl- 1997. 36, N o . 12
Scheme 1. Synthesis of water-soluble azo-dye rotaxanes
Table 1. Selected physical and spectroscopic data for 4ac3b. 4ac3b, and
4a [a].
HX),8.44(d, J = 8 H z , 1H;H,),828(s,lH;HD,w),8.26(s,lH;HD,D),8.14(d
J = 9 Hz,2 H ; HG.),8.02 (d, J = 9 Hz, 2 H ; HG),8.0-7.9 (m, 7 H ; Hc, H,, H,, H,.,
OH-3), 4.79 (d, J = 3 H z , 7 H ; H-l), 4.49 (t. J z 5 H z . 7 H ; OH-6), 3.7-3.1
146.94, 146.77, 144.81, 144.56, 141.14, 140.74, 139.80, 139.52, 133.29, 133.14,
130.87, 130.54, 128.35, 127.83, 126.77, 126.58, 125.76. 12549, 124.57, 124.47,
122.22, 121.37, 118.06[b], 101.85, 81.11, 73.01, 72.39. 71.88, 59.61; UV/
Vis: i,,,Jlg&) = 567 nm (4.75); negative-ion ESI-MS: ?n/z = 493.3 [ M - 4 N a + I 4 - ,
658.1 [ M - 4 N a + + H c ] " ,
987.7 [ M - 4 N a + + 2 H + l 2 - ,
correct for
4 a c 3 c : ' H N M R : 6 =16.19 (s, 2 H ; HE),8.32 (d, J = 8 Hz. 2 H : HA),8.29(s. 2 H ;
6.93 (s. 8 H ; cyclophane arenes), 3.64 (s, 24H; OMe), 3.5-2.6 (m, 32H; N + C H , ,
N+CH,CH,, and OCH,), 1.32 (m. 8H;OCH,CN,), 1 17 (t. J = 7 H z . 1 2 H ;
N+CH,CH,); I3C NMR: 6 =171.07, 152.86[b], 149 67. 146.94, 144.66, 141.46,
138.14, 135.26. 132.43, 130.35, 127.08, 12628. 125.74. 123.57, 120.53, 117.63,
104.01, 70.97[b], 55.86, 54.92, 42.68, 28.01, 25.05, 6.67; UV/Vls: ;.max(lge)=
567 nm (4.82); negative-ion ESI-MS: m/z = 920.4 [ M - 2Nat]'-, correct for
4a: ' H N M R : 6 =16.18(s, 2 H ; HE).
8.42(d, J = 8 Hz. 2 H . HA),8 26(s, 2 H ; HD),
8.06(ABq. J = 9 Hz,8H;HG,H,),7.91 (brs,2H, H C ) , 7 . 8 3 ( d , J = 8 Hz,2H;H,);
UV/VJS: ;.,,Jge)
= 562 nm (4.71); negative-ion ESI-MS: mjz = 209.6 [ M 4 N a + l 6 - , 279.9 [ M - 4 N a + + H + I 3 - , 420.2 [ M - 4 N a - + 2 H C ] ' - , correct for
[a] 'H (500 MHz) and "C (125 MHz) NMR spectra were recorded in [D,]DMSO,
and UV!Vis spectra in DMSO unless otherwise stated. [b] Two coincident
0 VCH Verlagsgesel[schaft mbH. 0-69451 Weinheim,1997
0570-0833~97j3612-1311317..FO+ SOj0
2 x 1 0 3 ~ - ' ) , whereas 4bc3b does not
( K < 2 0 M - ').[*l w e plan to explore the effects
of rotaxane encapsulation on the stability
and photo~hemistry[~]
of these dyes.
Experimental Section
:E @
Scheme 2. Structures o f 4 b c 3b and 4 b c 3c as well as some of the NOEs observed (double-headed arrows
indicate NOEs in both directions)
We also synthesized azo-dye rotaxanes with cyclophane 3c.1'1
In the presence of 3c, la and l b couple with 2 to give rotaxanes
4a c3c or 4b c 3c as the exclusive azo-dye product; no non-rotaxanated dye 4a or 4b is formed, although some by-products
are produced due to dediazotization. The rotaxanes were isolated as their sodium salts in 46 and 40% yields, respectively. They
precipitate from the reaction mixtures as [4ac3c]'-.[3~]~+
[4bc 3c1' - .[3c]' salts ; they were filtered off and purified by
column chromatography, then ion-exchanged to the sodium
salts. The 'H NMR spectra of these cyclophane rotaxanes are
considerably simpler than those of their CD analogues due to
both the higher symmetry of the cyclophane and to the cyclophane's aromatic ring current, which disperses the signals of
the guest. For example, for 4bc3c H,, H,, Me,, and H, are
shifted upfield by A6 = 0.90, 2.08, 0.51, and 1.75, respectively,
showing that these protons reside inside the cyclophane.
DPFGSE NOESY experiments confirmed that the central portion of the dye is buried inside the cyclophane's cavity. Some of
the observed NOEs are illustrated in Scheme 2.
We have shown that the hydrophobic effect can be used to
direct the synthesis of azo-dye rotaxanes with both CD and
cyclophane macrocycles. The cyclophane rotaxanes are formed
in higher yield and are easier to characterize spectroscopically.
All of these rotaxanes are more soluble (in most solvents) than
the non-rotaxanated dyes. They also aggregate less than their
non-rotaxanated analogues; for example, 4a forms stable bi+
(C VCH Verlagsgesellschaft mhH, 0-69451 Weinheim, 19Y7
4ac3b: NaNO, (41 mg, 0.59 mmol) was added to 4,4'-diaminoazobenzene (60 mg, 0.28 mmol) in aqueous HCI
(0.1 M, 10mL. 1.1 mmol) at 0-S'C. The solution was
stirred for 1 h, aqueous 3b (1 1.4 mM, 70 mL, 0.80 mmol)
added, and the mixture again stirred at 0-5 'C for 30 min.
This solution was added to a mixture of 2 (200mg,
0.56 mmol) and Na,CO, (99 mg, 0.93 mmol) in water
(8mL) and stirred for 3 h at 20°C. NaOAc (15g) was
added. and the mixture heated to 80°C. The precipitate
(4a) was separated from the supernatant by centrifugation. The product was then precipitated from the supernatant with acetone, washed with hot ethanol, dissolved
in water, recrystallized by addition of ethanol, purified
by chromatography on paper plates (Whatman 3MM)
eluting with MeCN/H,O ( l / l ) , and recrystallized from
DMSO/H,O (1i1) by addition of acetone. Yield: 89 mg
(1 5 Yo).
4ac3c: NaNO, (20 mg, 0.29 mmol) was added to 4.4'-diaminoazobenzene (30 mg, 0.14mmol) in aqueous HC1
( 0 . 1 9 ~ ,3 mL, 0.58 mmol) at 0-5°C. The solution was
stirred for 1 h, aqueous 3c (21 mM, 20mL, 0.42mmol)
added, and the mixture again stirred at 0-5 'C for 30 min.
This solution was added to a mixture of 2 (98mg,
0.28 mmol) and Na,CO, (SO mg, 0.47 mmol) in water
(2 mL) and stirred for 1 h. The solid was collected by centrifugation and purified by flash column chromatography
on silica eluting with M ~ O H / NH,CHO,/MeNO,
1) Concentration of the solution to 10% of its original
volume resulted in precipitation of the rotaxane, which was
isolated by filtration, washed with a minimum ofwater, and
dried in vacuo at 100'C/0.01 mm Hg to remove traces of
ammonium formate. Cation exchange was carried out with
Na+ Dowex SOWX8-400 (10 g), and recrystallization from
1: 1 DMSO/H,O by addition of ethanol. Yield: 122 mg
Received: January 2, 1997 [Z9955IE]
German version: Angew. Chem. 1997, 109, 1367-1370
Keywords: azo compounds cyclodextrins
taxanes supramolecular chemistry
- cyclophanes - ro-
[ l ] H. Zollinger, Color Chemistrj, 2nd ed., VCH, Weinheim, 1991.
[2] a) N. Yoshida, J. Chem. SOC.Perkin Truns. 2 1995.2249-2256; b) P. Bortolus,
S. Monti, J Phys. Chem. 1957, 91, 5046-5050; c) A . M . Sanchez. R. H.
deRossi. J: Org. Chem. 1996. 61, 3446-3451; d) M. Suzuki, H. Takai, K.
Tanaka, K. Narita, H. Fujiwara, H. Ohmori, Curbohydrnte Res. 1996, 288,
75-84; e) J. H. Jung, C. Takehisa, Y. Sakata, T Kaneda, Chem. Lett. 1996,
147-148; f) H. Hirai, N. Toshima, S . Uenoyama. BUN. Chem. Soc. Jpn. 1955,
58, 1156-1164.
[3] Cram et al. and Gokel et al. unsuccessfully attempted to prepare azo-dye rotaxanes from crown etheridiazonium salt complexes: G. W. Gokel, D. J. Cram, J.
Chem. SOC.Chem. Commun. 1973,481-482; J. R. Beadle, D. M. Dishong, R. K.
Khanna, G. W. Gokel, Tetrahedron 1954,40, 3935-3944.
[4] Hydrophobic binding has been used to prepare rotaxanes: a) S . Anderson,
H. L. Anderson, Angeu,. Chem. 1996, 108, 2075-2078; Angew. Chem. Int. Ed.
Engl. 1996,35,1956-1959; b) G. Wenz, ihid. 1994,106,851 -870 and 1994,33,
803-822; c) A. Harada, J. Li, M. Kamachi, J Am. Chem. SOC.1994, 116,
3192-3196; Nature 1992,356, 325-327; d) M. Kunitake, K. Kotoo, 0. Manabe, T. Muramatsu, N. Nakashima, Chem. Lett. 1993,1033-1036,e) G. Wenz,
B. Keller. Angew. Chem. 1992,104,201-204; Angew. Chem I n ! . Ed. Engl. 1992,
31, 197-199; f) R. S. Wylie, D. H. Macartney, J. Am. Chem. Soc. 1992, 114,
3136-3138;g) R. Isnin,A. E. Kaifer. ihid. 1991,113,8188-8190; h) H.Ogino,
ihrd. 1981, 103. 1303-1304.
[5] Negative-ion ESI-MS measurements were carried out on a VG-Bio Q instrument. We are grateful to Dr R T. Aplin for recording these mass spectra.
[6] J. Stonehouse, P. Adell, J. Keeler. A. J. Shaka, J . Am. Chem. Soc. 1994, 116,
6037-6038; K. Stott, J. Stonehouse, J. Keeler, T-L. Hwang, A J. Shaka, ihid.
1995, 117, 4199-4200. The selective DPFGSE sequence made use of a 180"
Gaussian pulse of 40 or 80 ms duration and 1 ms gradient of S . 5 : 8 : 8 Gcm-'.
Mixing times of up to 200 ms were used, and all observed NOEs were negative.
0570-0833/97/3612-1312$ 17.50+ SOj0
Angeir. Chem. Inr. Ed. Engl. 1997, 36, No. I2
- rsi
[7] Cyclophane 3c was synthesized according to Diederich et al.: S B. Ferguson,
E. M. Sanford, E. M. Seward, F. Diedench, 1 Am. Chem. SOC.1991,113,54105419.
181 Aggregation constants were determined by ' H N M R spectroscopy in DLO at
298 K in the concentration range 1 0 ~ 2 - 1 0 ~ 5 ~ .
191 Several photochemically interesting rotaxanes have been investigated: a) D. B.
Amahilino, P. R. Ashton. V. Balzani, C. L. Brown, A Credi, J. M J. Frechet.
J. W. Leon. F. M. Raymo. N. Spencer, J F Stoddart, M. Venturi, J Am. Chem
Sot. 1996. / / a , 12012-12020; b) N. Solladie, J.-C. Chamhron, C. 0. DietrichBuchecker. J.-P. Sauvage, Angew. Chem. 1996.108.957-960; Angew Chen?.Inr
Ed. EngI. 1996.35.906-909; c) A. C. Benniston, A. Harriman, V. M. Lynch. J
Am Chrm Soc. 1995, 117. 5275-5291; d ) J.-C Chambron, A Harriman. V
Heitz. J:P. Sauvage, ihid. 1993,115. 6109-6114; e) P. L. Anelli, P. R. Ashton.
R. Ballardini. V. Balzani, M. Delgado. M. T. Gandolfi. T. T. Goodnow, A. E
Kaifer. D Philp. M. Pietraszkiewicz. L. Prodi, M. V. Reddington, A. M. 2
Slawin. N Spencer, J. F. Stoddart. C. Vicent, D. J. Williams. ibid. 1992, 114,
193--2 I X
1) GaCI,
2) MeLi
3) HzO
76%,49%[b], 41%[c]
Friedel- Crafts P-Silylvinylations**
Masahiko Yamaguchi,* Yoshiyuki Kido,
Akio Hayashi, and Masahiro Hirama
The Friedel Crafts reaction is a fundamental method for
converting aromatic C - H bonds to C - C bonds. Although
Friedel-Crafts alkylations and acylations are often used in organic synthesis, the corresponding vinylations have not been
successful. Attempts at vinylation using either ethyne o r vinyl
halides have given polymeric substances and 1,1-diarylethanes,
even when the arenes are present in large excess."] This is due to
the instability of the vinylated products under the reaction conditions. Even 2-propenylations gave very low yields, and formed
various by-products.Iz1 Low efficiency in generating the electrophilic species may be another reason why the electrophilic
vinylations failed. We report here the Friedel- Crafts (E)-asilylvinylation of aromatic hydrocarbons promoted by GaC1,
This reaction is a direct C,-olefination of arenesr3]that proceeds
via novel organogallium intermediates.
An aromatic hydrocarbon (1 equiv) and trimethylsilylacetylene (3 equiv) were treated with GaCl, (3 equiv) in a mixture of methylene chloride and methylcyclohexane at - 78 "C.
After 30 min, methyllithium (9 equiv) in ether was added, and
the (E)-[(p-trimethylsilyl)vinyl]arene was obtained by aqueous
workup (Scheme 1). The C - C bond was formed at the a-carbon
atom of the silylacetylene, and the (E)-configuration of the
product was determined by 'H NMR spectroscopy. When only
one equivalent of silylacetylene and GaC1, were used the yield
was much lower. The regioselectivity of the aromatic substitution indicates an electrophilic mechanism,[41and is consistent
with the low reactivity of chlorobenzene, which can be used as
solvent. Steric factors are also important. F o r example, 2,6dimethylnaphthalene reacted a t C-4 rather than at the most
reactive position (C-I), and a considerable amount of 2-vinylated product was obtained from naphthalene. The electrophilic
species involved in this reaction appears to be considerably
[*I Prof. Dr M. Yumaguchi. Y Kido
Faculty of Pharmaceutical Sciences, Tohoku University
Aoba. Sendai 980-77 (Japan)
Fax: Int. code +(22)217-6811
Dr. A. Hayashi. Prof. Dr. M. Hirdma
Department of Chemistry. Graduate School of Science
Tohoku University. Sendai (Japan)
[**I This work was \upported by a Grant-in-Aid for Scientific Research from the
Ministry of Education. Science, Sports and Culture. Japan (no. 07554065 and
08404050). We also thank the Shin-Etsu Chemicals Co. Ltd for the generous
gifts of silicon reagents.
AnKen. C h m
ELI Engl. 1997, 36, N o . 12
53%[a,d], 36%[c]
Scheme 1. GaCI,-promoted /J-silylvinylations of arenes. The reaction sites on the
starting materials are marked with arrows; the relative regioselectivity in each case
is given in square brackets. [a] Yield determined by gas chromatography.
[b] Reaction in chlorobenzene. [c] Molar ratio GaC1,:acetylene:arene =
1 0:l.O: 1.0. [d] Molar ratio GaC1,:acetylene:arene = 2.0:2.0-1.0
bulky. Unlike previously reported Friedel - Crafts vinylations
and alkenylations,['.
this reaction does not require excess
arene. Therefore, nonvolatile polycyclic arenes can be /-isilylvinylated without the necessity to carry out the tedious separation of a large amount of unconverted starting materials.
There was very little divinylation and isomer formation under
the present reaction conditions. Triethylsilyl- and tertbutyldimethylsilylacetylene reacted analogously with rn-xylene
to give the corresponding products in yields of 54 and 5 2 % ,
respectively. When I-methylnaphthalene was treated with
GaCl, and ethyne at - 78 "C, the arene was consumed within
30min to give a polymeric compound. Thus, the silyl group
prevents the olefin group on the products from undergoing side
The (8-silylviny1)arenes are useful synthetic intermediates for
a variety of aromatic compounds (Scheme 2). For example, the
trimethylsilyl group can be removed by trifluoroacetic acid to
give the parent vinylarene, and epoxidation followed by treatment with an acid gives an aryla~etaldehyde,[~]
which can be
reduced to a n arylethanol.
The use of GaC1,[61in these /I-silylvinylations is critical; other
Lewis acids (AlCl,, GaBr,, InCI,, SnCl,, SbCl,, SbF,), protic
acids (CF3S03H, HCI), and heterogeneous acids (Na-Mont-
VCH Wrlugsgesell.whoft mbH. 0-69451 Weinheim. 1997
0570-0833/97/3612-1313 $ 1 7 SO+ .SO'O
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azo, rotaxanes, dye
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