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Double Helical Octaphenylene.

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[I] A. F. Hebard, M. J. Rosseinsky, R. C. Haddon, D . W. Murphy, S. H. Glarum,
T. T. M . Palatra, A. P. Ramirez, A. R. Kortan, Nature 1991, 350, 600.
121 P.-M Allemand, K. C. Khcmani, A. Koch, F. Wudl. K. Holczer, S. Donovan,
G. Gruner. J. D. Thompson. Science 1991,253, 301.
[3] Review on fullerenes: M. S. Dresselhaus. G. Dresselhaus. P. C. Eklund,
Scirnce of Fu1ler.ene.s and Curhon Nanotuhes, Academic Press. NY, 1996.
[4] Procedings uj thr Syniposium on Recent Advances in the Cheniistry and Physics
uf Fullerenes and Related Materials (Eds.: R. S. Ruoff, K M. Kadish). The
Electrochemical Society Proceeding Series, Pennington, NJ, 1995.
[5] Pro,qw.s ni Fullerene Research (Eds.: H. Kuzmany, J. Fink. M. Mehring,
S. Roth), World Scientific Publishing. London, 1994.
161 0. Zhou, J. E. Fischer. N. Coustel, S. Kycia, Q. Zhu, A. R. McGhie, W. J.
Romanow, .I.P. McCauley, Jr., A. B. Smith 111, D. E. Cox, Nature 1991, 351,
462; P. W. Stephens. L. Mihaly. P. L. Lee, R. L. Whetten, S.-M. Huang, R.
Kaner, t’. Diederich, K. Holczer, ihid. 1991, 351, 632.
[7] J. E. t‘ischer, G. Bendele, R. Dinnebier, P. W. Stephens, C. L. Lin, N.
Bykovetz. Q. Zhu. J Phys. Chem. Solidc 1995. 56, 1445.
181 R. M. Fleming, A. P. Ramirez, M. J. Rosseinsky, D. W. Murphy, R. C. Haddon, S. M. Zahurak, A. V. Makhija, il’nture 1991, 352, 787.
.
L e f t . 1992. 68, 1050; M.-Z. Huang, Y.-N.
[9] M. P. Gelfand, J. P. Lu, P h y ~Rev.
Xu. W. Y. Ching. J. Chrm. Phj’.y. 1992, 96, 1648.
[lo] F. C. Zhang, M. Ogata, T. M. Rice, Phys. Rev. Lett. 1991, 67, 3452.
. Thompson, R L. Whetten, S.-M. Huang, R. B. Kaner,
[ l l ] G. Sparn, .ID.
F. Diederich, K. Holcrer, I’1z~v. Rev.Lett. 1992. 68, 1228.
[11] S. Chakravarty, M. P. Gelfand. S. Kivelson. Science 1991. 254, 970; C. M.
Varma. J. Zaanen, K. Raghavachari, ihid. 1991, 254, 989.
[I31 0.A. Bochvar, E. G. Gal’pern, Dokl. Akud. Nunk. S S S R 1973, 209,
610.
[I41 F. Negri. G. Orlandi, F.Zerbetto, J. Am. Chem. Soc. 1992, 114, 12909.
[I51 H. A. Jahn. E. Teller, Proc. R . Soc. London A 1937, 161, 220.
[I61 R. E. Douthwaite, A. R. Brough, M. L. H. Green. J. Chem. C‘onini. 1994,267;
A. Penicaud. A. Perez-Beniter, R. Gleason V, E. Mufioz, R. Escudero, J Am.
Chern. Sue. 1993, 115,lO 392; U. Billow, M. Jansen, J. Chem. Cumm. 1994,403;
C. Janiak. S. Muhle, H Hemling, Polyhedron 1995, 15, 1559.
1171 a) P. Bhyrappa, P. Paul, J. Stinchcombe, P. D. W Boyd, C. A. Reed, J. A m .
Chem. Soc. 1993. f 1 5 , l I 004: P. D. W. Boyd. P. Bhyrappa, P. Paul, J. Stinchcombe. R. D. Bolskar, Y Sun, C. A. Reed, ibid. 1995. 117, 2907; b) M. M.
Khaled, R. T. Carlin, P. C. Trulove. G. R. Eaton, S. Eaton, ihid. 1994, 116,
3465: c) P. C. Trulove, R. T. Carlin. G. R. Eaton, S. Eaton, ihid. 1995. 1 f 7 .
6265; see also ref. [3].
[I81 P. Paul. Z. Xie, R. Bau, P. D. W. Boyd, C. A. Reed, J. An?. Chem. Soc. 1994,
//6,4145; PPN = bis(tripheny1phosphane)iminium.
[ 191 12.2.21Crypt = 4.7,13,16,21,24-hexaoxa-l,10-diazohicyclo-[8.8.8]hexacosane.
1201 T. F. k’issler, M. Hunaiker. Inorg. Chem. 1994,33,5380;Z. Anorg. A/%. Chem.
1996, 622. 837; J. D. Corbett, Chrm. Rev. 1985, 85, 383.
[?I] Structure determination of 1.4 toluene: a crystal plate of dimensions
0.30 x 0.20 x 0 08 mm3 was inserted into a glass capillary after decantation of
the solvent. Lattice parameters at 293 K: a = 23.84(2), b =15.36(1), c =
28.90(2)pm, = 112.00(6)‘; V = 9814.9 x lo6 pm3; at 113 K : a = 22.696(4),
h = 15.580(2). c = 27.523(4) pm. f l = 106.20(2)’ ; V = 9346.0 x lo6 pm3. space
= 1.365 g’cm-’. Data collection: STOF!
group Cc (monoclinic), Z = 4. pCaicd
IPDS. Mo,, radiation, 20,,, = 48.28” (Image plate distance 80 mm),
1‘=113 K, of 26093 reflections 12086 were independent (R,,, =16.3%).
R , =10.9% for 962 parameters and 5228 reflections with 1>3u(I),
W R = 28.3% (based on F’). Structure solution (direct methods) and refinement (based on F 2 )were carried out with SHELXS-86 and SHELXL-93 programs. respectively (G. M. Sheldrick, Universitdt Gottingen). By applying direct methods. a [K([2.2.2]crypt)]unit could be localized in the space group C2/c
for both the room-temperature and low-temperature data. The maxima of
diffcrcnce electron density are situated on a sphere and reveal portions of fiveand six-membered ring structures. Several models were considered for the
refinement of the fullerene molecule. Application of a model with complete
orientational disorder of the fullerene molecules using a hollow sphere with the
integral electron density of 60 carbon atoms (Bessel function) did not lead to
a significant improvement. The difference density maxima could be fitted.
and the structure further refined with a localized model in space group Cc.
A tramformation of the coordinates to C2,’c showed that the twofold rotation
axis or the fullerene molecule is tilted with respect to the crystallographic
trotation axis. A refinement with a corresponding 50:50 split model led to
a pool- fit with the data and lower resolution of the electron density. Although
the space group C2:c cannot be excluded by the current data, the refineompleted in Cc in two blocks with a total of 460 coupled parameters
(the displacement parameter of neighboring carbon atoms of the fullerene
molecule were constrained by means of the DELU (SHELXL93) command)
Maximum and minimum residual electron density: 0.9 and -0.7 e k ’ . Crystallogi-aphic data (excluding structure factors) for the structure reported
in this paper have been deposited with the Cambridge Crystallographic
Data Center as supplementar) publication no. CCDC-100-074. Copies can be
obtained free of charge on application to The Director. CCDC. 12 Union
Road. GB-Cambridge CB2 1EZ (Fax: Int. code +(1223) 336-033, e-mail:
deposit!a chemcrys.cam ac.uk)
488
VCH Verlagagesel1,srhaJtmhH, 0-69451 W’einheim, 1997
[22] S. Liu, Y-J. Lu, M. M. Kappes, J. A. Ibers, Science 1991, 254, 408; W. I. E.
David, R. M. Ibberson, J. C . Matthewman, K. Prassides. T. J. S. Dennis, J. P.
Hare, H. W Kroto, R. Taylor, D. R. M. Walton, Nature 1991, 353, 147.
[23] W. C. Wan, X Liu, G. M. Sweeney, W. E. Broderick, J. A m . Chem. Soc. 1995,
117,9580.
[24] EPR spectra were recorded on a Varian E-I2 EPR spectrometer.
[25] Magnetic susceptibility measurements were carried out with a SQUID magnetometer (MPMS 5. Quantum Design) at a magnetic field of 1000 G. An aluminum crucible in a suprasil tube (diameter = 5 mm) was used as a sample
holder, and its signal experimentally corrected. For the determination of the
paramagnetic molar susceptibility, the diamagnetic contribution for the two
[K([2.2.2]crypt)] moieties and three D M F molecules (x:] = - 624.6 x
cm’rnol~’[26]) were substractedfrom the total molar susceptibility. The
contributions of C,, to the total susceptibility can be ignored as the diamagnetic and paramagneticcomponents cancel out [3.27]. Measurements (30 mg samples from different reactions) on analytically pure powders of 1 ‘ 3 D M F gave
identical temperature dependencies. Minor contributions from molecular oxygen, which also appear in pure C,, [27], cannot be excluded. Further investigations on the magnetic properties and the appearance of a shoulder at about
50 K (Figure 2) are yet to be carried out.
[26] A. Weiss, H. Witte, Mugnetochemie, VCH, Weinheim. 1973.
[27] R. C. Haddon, L. F. Schneemeyer. J. V. Waszcrak, S. H. Glarum., R. Tycko, G.
Dabbagh, A. R. Kortan, A. J. Muller, A . M . Mujsce, M. J. Rosseinsky, S. M.
Zahurak, A. V. Makhija, F. A. Thiel, K. Raghavachari, E. Cockayne, V. Elser,
Nature 1991, 350. 46; R . S. Ruoff, D. Beach, J. Cuomo. T. McGuire, R. L.
Whetten, F. Diederich, J. Phys. Chem. 1991, 95, 3457; W Luo, H. Wang, R.
Ruoff, J. Cioslowski, S. Phelps. Phys. Rev. Lett. 1994, 73, 186.
[28] 2.5 p,in(PPN):C&CI-.CH,CNand
1.0-2.3 p,in(PPN):C& [17a]; adirect
comparison is not possible as no diamagnetic corrections are given.
Double Helical Octaphenylene**
Andrzej Rajca,” Andrej Safronov, Suchada Rajca,
and Richard Shoemaker
Chiral n-conjugated molecules and polymers attract continuing interest as synthetic challenges and organic materials with
interesting electronic properties.[’ -41 Our strategy in design of
such materials centers on a double helical n-conjugated system
that combines chirality with molecular entanglement and very
high barriers for racemization. Such molecules or polymers may
facilitate better three-dimensional interactions and chirooptical
properties. In addition, there is the intriguing question about the
effect on electrical conductivity, especially in the presence of
external magnetic fields.[2-41
The approach to the double helix is inspired by the achiral
carbon allotrope, “three-dimensional graphite”, proposed by
Riley el al.[’] This structure may be conceived as composed of
double helical polymers, in which two polyphenylene helices are
intertwined or tetra-o-phenylene units sequentially annelated.
The beauty of this double helix, the important materials properties associated with polyphenylenes, such as electrical conductivity and electroluminescence, and the very high barriers for
racemization of tetra-o-phenylenes provide impetus for synthesis of fragments of this double helix such as tBu-substituted
octaphenylene 1 (Figure 1).[6
Double helices are typically assembled from single strands by
metal ion complexation, hydrogen bonding, e t ~ . [ ~ .An alter-
[*] Prof. A. Rajca, Dr. A. Safronov, Dr. S. Rajca, Prof. R. Shoemaker
Department of Chemistry
University of Nebraska
Lincoln, NE 68588 (USA)
Fax: lnt. code +(402)472-9402
e-mail: arajca(u~unlinfo.unl.edu
[**I
This research was supported by the National Science Foundation (DMR9204826 and CHE-9520096). We thank Dr. R. Cerny of the Nebraska Center
for Mass Spectrometry for the mass spectral determinations. We thank Dr.
Charles R Ross, I1 for the help with the X-ray crystallography and graphics.
0570-0833~97i3605-04SX$ 15.OOt . 2 5 0
Angew. Chem. Int. Ed. Engl. 1997, 36. No. 5
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I
I
\ 1
I /
(69%)
$::
+ 2 +
1) tBuLj
1) tBuLi
2)MeOH
1) nBuLi
t
4
f
11) tBuLi
l 2 j CuBrz
Figure 1 . Top: Space-filling model for a double helical polyphenylene molecule,
derived from a three-dimensional carbon net; bottom left: Double helical octaphenylene I ; bottom right: Space-filling model for 1. The two helices are colored
red and blue; tBu groups are shown in grey/black.
Scheme 2. Synthesis of octaphenylene 1. Except for the reaction step leading to
tetraphenylene 4, which was carried out in THF, the aryldilithium compounds were
generated by adding 2.5 M nBuLi in hexane (1 equiv) or 1.7 M tBuLi in pentane
( 2 equiv) to the bromoaryl compound in ether at 78 'C. After 2 h a t - 78 ' C , dry
CuBr, (3 equiv) was added. The reaction mixture was allowed to warm to room
temperature over 12 h and then usual aqueous workup was performed.
+
native route to a double helix is based on sequential connection
of doubly helical fragments; this may be advantagous in rednc-ing the number of degrees of freedom when kinetically controlled, irreversible reactions of organic synthesis are employed
(Scheme 1). We report here on the synthesis of octaphenylene 1,
the first example of a double helical z-conjugated hydrocarbon,
by sequential annelation of two tetra-o-phenylene fragments.
+
~
5 is confirmed by the presence of an NOE (12%) between H8
and H9 (and the other symmetry-related pair). After dilithiation
of 5 and subsequent oxidation with CuBr, , 1,6, and 7 could be
isolated. The structure of the double helical octaphenylene 1 is
confirmed by mass spectrometry (HR-MS) and NMR spectroscopy.['*] In the mass spectrum (EI), the most intense cluster
(relative intensity 100 %) in the range rnjz 100 1350 corresponds to M + ; the M ' , [ M + I]', [ M +2]', [ M + 3 ] + peaks
have masses within less than 2 ppm of the calculated values and
possess adequate relative intensities for C,,H,,, The spectrum
shows only three other clusters with relative intensities greater
than l o % , which are identified as follows: [ M CH,]' (29%),
[MI" (15%), [ M - 2CH,I2+ (50%). The ' H N M R spectrum
(CDC1,) contains two resonances for tBu groups (36j36) and a
set of five resonance signals (4/4/4/4/4) for the arene protons;
Scheme 1. Formation o f a double helix by stepwise linkage of double helical frag3C DEPTjNMR spectra corroborate the spectral assignment.
ments.
In the arene region of the ' H N M R spectrum, a 2D-COSY
correlation indicates that the three most downfield resonances
Following the double Li/Br exchange on 2,2'-dibromo-4,4'(dd, d, d, J = 8, 2 Hz) and the two most upfield resonances (d,
di-tevt-butylbiphenyl and 2,2',6,6'-tetrabromo-4,4'-di-tert-butyl- d, J = 2 Hz) correspond to protons at the outer and inner benbiphenyl, the resultant dilithiobiphenyls are oxidized with
zene rings, respectively.
CuBr, to give 2 and 3, respectively (Scheme 2, Table 1).[11-141
The NOE studies were carried out for 1 in CD,Cl,. The
When tetraphenylene 3 is subjected to LijBr exchange, and reac'H NMR spectra in CDCl, and CD,C1, are similar, except for
tion mixture is quenched with MeOH, the 4,13-dibromo-substidifferences in chemical shifts. The 2D-ROESY experiment (Figtuted tetraphenylene 4 is obtined as the major product; the
ure 2) gives two negative-phase cross peaks, between protons
arene protons of 4 show no NOE effect ( < 1 YO).
Moreover, the
H3 and H5 and H3 and H4 (integrated ratio of 5/1).["] In the
desired 4,5-dibromo-2,7,10,15-tetra-tert-butyl(tetra-o-phenyl- I D NOE experiment, the H3,H5 and H3,H4 proton-proton
ene) 5 is not detected in the reaction mixture. Similarly, attempts
contacts give an NOE of 10 '30and no NOE ( < 2 % ) , respectiveto selectively dimetalate 2 failed. Apparently, the stablizing efly. The H3,H5 contact (v = 3.0 A)[''] is similar to the H8,H9
fect of the ion triplet, which is invoked for planar 2,2'-dilithiois charactercontact in 5, and the H3,H4 contact ( r = 3.8 ..k)[201
biphenyl and other analogous dilithium compounds, does not
istic of the double helix of 1.
apply to these nonplanar, rigid derivatives of biphenyl.['5
UV/Vis spectra (cyclohexane) for 1 (in,,,= 219, 253 (sh), 288
When a 1 : 1 mixture of 2,2'-dilithio-4,4'-di-tert-butylbiphenyl (sh) nm) and 2 (2,,, = 219, 242 (sh), 278 (sh) nm) possess simiand 2,2'- dilithio-4,4'-di-tert-butyl-6,6'-dibromobiphenylis
lar spectral
These spectra can be compared to
treated with CuBr,, 5 can be separated from the symmetrical
the longest wavelength absorptions for oligo-p-phenylenes(247,
coupling products 2 and 3 (Scheme 2, Table 1). The structure of
279, and 294 nm for biphenyl, terphenyl, and quaterphenyl, re~
~
~
Angrw Chem Int Ed Engl 1997, 36 No 5
0 VCH VcrluRAgcxIl~chafrmhH
0-69451 Wcmheun 1997
0570-083j 97 3605-04895 15 00+ 25 0
489
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Table 1. Selected physical data for compounds 1-3, and 5-7.
1: white powder, m.p. 382-384'C, yield 4 % : LRjHR EIMS: m / z (ion type, relative
intensity in YOfor m/z 100 ~1350,deviation for the formula): 1055.72964 ( [ M 3]',
12%, 0.3ppm for 12C,,13C,'H,,). 1054.72599 ( [ M + 2 ] + , 40%, 0.6ppm for
'ZC,,'3CC,LH,,), 1053.72216 ( [ M I]', 90%, 1.0 pprn for 12C,,13C1H,,),
1052.71815([M]t, 100%,1.7 ppmfor'ZC,,'H,2), 1037.69571 ( [ M - CH3]+,29%,
0.7ppmfor 'ZC,,'H8g); 526([M]'+, I S % ) , 511 ( [ M - 2 C H J 2 + , 5 0 % ) ; ' H N M R
(500 MHr, CDCI,, 'H-'H COSY cross peak in the region of the arene protons):
6 = 7.31 (dd, JI = 2, J2 = 8,4H, 7.19,7.08), 7.19 (d, J = 2 , 4 H , 7.31), 7.08 (d, J = 8,
4 H , 7.31), 6.95 (d, J = 2, 4 H , 6.68), 6.68 (d, J = 2, 4 H , 6.95), 1.36 (s, 36H), 1.19
(s, 36H); ' H N M R oftheareneprotons(500 MHr, CD,CI,, T, [s]): 6 =7.42(1.6),
7.14 (1.6), 7.08 (1.6), 7.01 (1.7), 6.85 (2.24); ROESY (500 MHz, CD,CI,): cross
peaks at 6 =7.14/7.01 and 7.14/6.85 with integrated ratio of 5 / l ; NOE (500 MH7,
CD,CI,, 7.14): 6 =7.01 ( l o % ) , 6.85 ( < 2 % ) ; 13C{'H} NMR/DEPT (125 MH7,
CDC1,):S =149.7(q), 148.5(q), 142.7(q),142.4(q), 140.4(q), 139.0(q),136.9(q),
129.9(CH), 125.6(CH), 124.7(CH), 123.8(CH), 123.1 (CH), 34.5(q), 34.4(q),
31.5 (CH,), 31.4 (CH,).
+
+
2: white solid, m.p. 270 271 ' C , yield 69%; elemental anlysis cdlcd for C,,H,,:
C
90.85, H 9.15: found: C 90.64, H 9.01; HR EIMS: m/z (ion type, relative intensity
in % for m/z 40-600, deviation for the formula): 530.38214 ( [ M +2]',
8 % , -0.3 ppm for 1ZC,,'3CC,'H,,), 529.37826 ( [ M+1]', 41 %, -1.3 ppm for
'2C,,i3C'H,,),
528.37525 ( [ M I ' , 95% -0.7 ppm for 'ZC40'HL8), 513.35188
( [ M - CH,]+, l o o % , -0.5 ppm for 'ZC3g'H45);
' H N M R (500 MHz, CDCI,, 'H'H COSY cross peak in the region of the arene protons): 6 =7.29 (dd, JI = 2,
J,=8,4H,7.16,7.09),7.16(d,J=2,4H,7.29),7.09(d,/=8,4H,7.29),1.32(~,
36H); "C{'H} NMR/HT:TCOR (125 MHz, CDCI,, 'H cross peak): 6 =149.6,
141.9, 138.8, 129.4 (7.09), 126.8 (7.16), 123.9 (7.29), 34.5, 31.4 (1.32).
3: white powder, m.p. 310-331 'C, yield 17%; elemental analysis calcd for
C,,H,,Br,:
C 56.90, H 5.25; found: C 56.82, H 5.43; HR EIMS: mjz (ion type,
relative intensity in % for m/z 805-865, deviation for the formula): 848.01482
( [ M +8]+, 9 % , -6.3 ppm for 'ZC40iH448'Br4),846.024842 ( [ M +6]+, 27%, does
844.01503 ([M + 4 ] + , 28%, -1.8ppm for "C4,not fit 'zC4,'H,,7'Br8'Br,),
'H4,7yBr,8'Br,), 842.01798 ( [ M+2]', 20%, -2.8 ppm for '2C,,1H4,79Br,8iBr).
840.01956 ([MI+, -2.3 ppm deviation for 'ZC4,'H,,79Br,); ' H N M R (CDCI,):
6 =7.39(d, J = 2 , 4 H ) , 7 . 2 0 ( d , J = 2,4H), 1.28(s,36H); '3C('H}NMR(CDCI,):
6 =152.4, 143.0, 137.2, 128.1, 123.5, 123.1, 34.7, 31.1.
5 : powder, m.p. 220-222"C, yield 19%; LRjHR EIMS: m / z (ion type, relative
intensity in "/o for m/z 100-710, deviation for the formula): 689.19534 ( [ M 5]+,
21 YO,0.8 ppm for '2C,,'3CiH,,R'Br,),
688.19242 ( [ M +4]+, 55%, 0.2 ppm for
iZC,,1H,,8'Br,), 687.19671 ( [ M +3]+,43%, 1.8 ppmfor 'ZC,,'3C'H 4 6 " 8 r "Br),
686.19351 ( [ M + 2 ] + , 100%, 1.6 ppm for 1ZC,,1H,,7yBr*'Br), 685.19888
( [ M I]', 23%, 1.6 ppm for '2C,,13C1H,,79Br,), 684.19460 ([MI+, 49%.
3.0 ppm for 1ZC4,'H,,79Br,), 671.17066 ( [ M- CH,]', 80%, 0.7 ppm for
12C,,'H,,'9Br81Br); ' H N M R (500 MHr, CDCI,, 'H-lH COSY cross peak in the
regionoftheareneprotons):S =7.45(d,J=2,2H,7.07),7.30(d,J= 2,2H,7.25),
7.25 (dd, JI = 2, J2 = 8, 2H, 7.30, 7.01), 7.07 (d, J = 2, 2 H , 7.45), 7.01 (d, J = 8,
2 H , 7.25), 1.34 (s, 18H), 1.28 ( s , 18H). NOE (500 MHr, CDCI,, 7.30): 6 =7.07
(12%). 7.01 ( < l X ) ; "C{'H} NMR/DEPT (125 MHz. CDCI,): 6 =152.0 (q),
150.0 (q), 143.4 (q). 141.5 (q), 138.3 (q), 137.4 (4). 129.0 (CH), 128.1 (CH), 125.1
(CH). 124.6 (CH), 124.14 (CH), 124.07 (9). 34.7 (9). 34.5 (q), 31.4 (CH,), 31.2
(CH,).
6: yellow powder, m. p. 125-130'C, yield 1 %; H R EIMS: m / z (ion type, relative
intensity in % for m / z 50-550, deviation for the formula): 526.36026 ([MI', l o % ,
0.6 ppm for 12C,,H,,), 511.33570 ( [ M - CH,]', 3%, -1.5 ppm for "C3,,'Hd,);
'HNMR(S00 MHr,CDCI3):6 = 7 . 3 2 ( d , J = 2,2H),7,25(dd, J, = 2,J2 = 8 , 2 H ) ,
1, ZH), 6.83 (d, J = 8, 2 H ) , 6.66 ( d , J
1, 2H), 1.34 (s, IXH), 1.30
7.16 ( d J
(s, 18H).
7:white powder, m.p. 135-141 C. yield 4 % ; L R EIMS: mlz (relative intensity in
% for mlz 500-1350): 1210.5 (45), 1211.5 (40), 1212.5 (100). 1213.5 (go), 1214.5
(75), 1215.5 (45). 1216.5 (15); cakd for C,,H,,Br,: 1210.6 (43), 1211.6 (38), 1212.6
(loo), 1213.6 (go), 1214.6 ( 7 5 ) , 1215.6 (46), 1216.6 (18): ' H N M R (500MHz,
CDCI,, 'H-'H COSY cross peak in the region of the arene protons): 6 =7.31 (d,
J=2,2H,7.14),7.29(d,J=2,2H,7.18),7.245(d,J=2,2H,6.94),7.18(dd,
J, = 2, J2 = 8, 2 H , 7.29, 7.08), 7.14 (dd, JI = 2, J2 = 8, 2H, 7.31, 6.97), 7.08 (d,
J = 8,2H,7.18),7.05 (d, J = 2,2H, 6.79),6.97(d, J = 8,2H,7.14), 6.94(d, J = 2,
+
+
-
-0
Figure 2. 2D-ROESY (500 MHz) spectrum for 1 in CD,Cl,. The ROESY cross
peaks are orangejred and labeled "3,5" and "3,4"; the orange/red cross peaks
adjacent to the diagonal are phase artefacts. The blue/purple cross peaks arc due to
residual Hartmann- Hahn effects.
connectivities between the benzene rings, is decreased but not
diminished compared to that of oligo-p-phenylenes.
The yields of symmetrical tetraphenylenes (with two C-C
bonds formed) isolated decrease sharply in the order 2 (69 %),
3 (1 7 YO),1 (4 Yo), whereas the amounts of the side products in
which only one C-C bond is formed, such as the dimer derived
and tetrafrom 2,2',6,6'-tetrabromo-4,4-di-tert-butylbiphenyl
phenylene dimer 7,increase. Notwithstanding the details of the
mechanism, the formation of tetraphenylene formally requires
two homochiral2,2'-dimetal biphenyl fragments; therefore, in a
racemic mixture, whenever heterochiral fragments combine
(one C-C bond formed) and the barrier for configuration inversion is high, competing reactions take over.
The synthesis of higher homologoues of 1 and, in particular,
the corresponding double helical polymer poses a synthetic challenge in which the formation of the tetra-o-phenylene ring in
high yield and the use of homochiral building blocks (and/or
high enantioselectivity) are prerequisites. The recently prepared
biphenylene dimer 8 partially satisfies these requirements;[ l
2H,7.245),6.79(d,J=2,2H,7.05),1.27(s,18H),1.141(s,18H),1.135(s,18H),
0.92 (s, 18H)' 13C('H}NMR/DEPT (125 MHz, CDCI,): 6 =150.5 (q), 149.5 (q),
149.3 (9). 148.1 (q). 145.2 (q). 143.4 (q), 143.3 (4). 142.3 (q), 139.6 (q), 139.3 (4).
138.0 (4). 135.9 (9). 135.7 (q), 128.5, 126.7, 126.3, 126.0, 125.6, 124.2, 124.0, 123.7,
123.0, 122.6, 122.4 (q). 34.5 (4). 34.4 (q), 34.3 (q), 34.2 (9). 31.33 (overlapped two
peaks), 31.27, 31.08.
spectively) .["I The bathochromic shift, which is attributed to
the extension of conjugation from 2 to 1, is relatively small
compared to that of oligo-p-phenylenes. Thus, the x-conjugation in 1, which accommodates the helical twist and meta, ortho
490
(2 VCH Verlugs~esdlschuftftmbH, D-69451 Wemheim. 1997
however, the reaction of 8 under conditions typical for the conversion of biphenylene to tetra-o-phenylene[231yields neither 1
nor its higher homologues as products.[241
O570-0833/97/3605-04903 15 OO+ 25 0
Angm Cheni Int Ed Engl 1997,36, Ao 5
COMMUNICATIONS
The development of efficient enantioselective methodologies
for the construction of tetra-o-phenylenes and less sterically
constrained biphenylene dimers is in progress in our laboratory.
Received September 4, 1996 [Z 9528IEl
German version A n g w Chrm 1997, 109, 504-507
Keywords: arenes
chirality
- double helices
*
polymers
[ l ] E. L. Eliel, S . H. Wilen, Sterrorhemisfry qf Organic Compound.s, Wiley. New
York, 1994; Chapter 14.
[2] J. D. Wallis. A. Karrer, J. D. Dunitz, Hrlv. Chim.A c f a 1986, 69. 69.
131 M. M W. Langeveld-Voss, R. A. J. Janssen, M. P. T. Christiaans, S. C. J.
Meskers, H. P. J. M. Dekkers, E. W. Meijer, J. Am. Cheni. SOC.1996,118,4908.
[4] Y. Miyamoto. S. G . Louie, M. L. Cohen, Phjs. Rev. Lett. 1996, 76, 2121.
[5] J. Gibson. M. Holohan, H. L. Riley, 1 Chem. Soc. 1946, 456; M. OKeeffe.
G. B. Adams. 0. F. Sankey. Phys. Rev. Left. 1992, 68. 2325; F. Diederich, Y
Rubin, AnyPiL. Clrem. 1992. 104. 1123; Angrw. Chrm. Int. Ed. Engl. 1992, 31.
1101.
[6] D. L. Gin. V. P. Conticello, R . H. Grubbs, J. A m . Chem. Sor. 1994,116,10934.
M A. Keegstra, S. D. Feyter, F. C. D. Schryver, K. Mhllen, Angew. Cheni.
1996, 108, 830. Angew. Cheni. Int. Ed. Engl. 1996, 35, 774.
[7] V. Enkelmanii. J Physique 1983,44, C3. G. Grem, G . Leditzky, B. Ulrich, G .
Leising. A h . Afotrr. 1992, 4, 36; M. Hamaguchi, H. Sawada, J. Kyokane, K.
Yoshino, Chrni.L e t / . 1996, 527.
[El A barrier for racemization in excess of 60 kcdl mol was reported for a tetra-ophenylene derivative: P. Rashidi-Ranjbar, Y -M. Man, J. Sandstrom, H. N. C .
Wong. J Org. Chem. 1989, 54, 4888
191 J. -M. Lehn, Anycw. Chcm. 1990, 102, 1347; Angew. Chcm. Znf. Ed. Engl. 1990,
29. 1304. J. -M Lehn, Supramolecular Chemrstrj, VCH, New York, 1995.
[lo] D. B. Amabilino. J. F. Stoddart. Chern. Rrv. 1995. 95, 2725.
[l I ] A. Rajca. A. Safronov, S. Rajca, C. R . Ross, 11, J. J. Stezowski, J. Am. Chem.
Soc 1996, 118. 1272.
[I21 G. Wittig, G Klar, Liebigs Ann. Chem. 1967, 704. 91.
[13] A small amount of biphenylene product is typically formed hut not isolated.
2.2'-Dibromo-4.4-di-terr-butylbiphenyl:
M. Tashiro, T. Yamato, J. Org. Chem.
1979. 44. 3037.
[14] For a review o n chemistry of tetra-o-phenylenes, see: T. C. W Mak, H. N. C.
Wong. Rip. ('urr. Chem. 1987, 140, 141.
1151 U . Schubert. W. Neugebauer. P. Yon R. Schleyer. J. Chenz. Soc. Chem. Comniun. 1982. 11x4: W. Neugebauer, A. J. Kos, P. von R. Schleyer, J Orgunomrt.
C h m 1982. 228. 107.
[16] A. Streitwiesei-. Act. Cheni. Re>. 1984, 17. 353.
[I71 0. Desponds. M. Schlosser, Tetrahedron 1994, 50, 5881.
1181 The largest crystals of 1 grown so far (90 x 90 x 180 mm) were too small for
analysis with a conventional X-ray diffractometer.
[I91 A. A . Bothner-By. R. W. Jeanloz. J. Lee, R. L. Stephens, C. D. Warren. J. An?.
Chm?.Sor. 1984, 106. 81 1 ; A. Bax. D. Davis, J. M a p , Reson. 63. 207, 1985.
[20] H - H distances in 1 are taken from an M N D O calculation on the parent
compound (with hydrogen atoms replacing tBu groups); AHc =
222.4 kcal mol (D,symmetry, grad norm = 2.6). M. .I.
S. Dewar. W Thiel. J.
An7. Chmi. Soc. 1977, Y9,489Y; J. J. P. Stewart. MOPAC93.00 Manual, Fujitsu
Limited, Tokyo, 1993.
[21] The spectral envelopes for 1 and 2 have some resemblance to those of sterically
crowded biphenyls. for example, 2,2'-dimethylbipheny1; see ref. [22].
[?2] H.-H. Perkampus, C'V-VJS.4rl~1.snjOrgunirCompounds, 2nd ed., VCH. Weinhelm. 1992, Part 2.
[23] H. Schwager. S.Spyrondis, K P. C. Vollhardt, J Organomel. Chem. 1990,382.
I91 and references therein.
[24] The control reaction of 2,7-di-tert-butylbiphenylene
under the conditions given
in ref. [23] resulted in a clean mixture of 2 and its isomer. A. Rajca, A.
Safronov. unpublished results.
~
Monitoring the Progress of Solid-Phase
Oligosaccharide Synthesis by High-Resolution
Magic Angle Spinning NMR: Observations of
Enhanced Selectivity for /?-Glycoside Formation
from a-1,2-Anhydrosugar Donors in Solid-Phase
Couplings**
Peter H. Seeberger,* Xenia Beebe,
George D. Sukenick, Susan Pochapsky, and
Samuel J. Danishefsky
The vital roles played by oligosaccharides in cell-cell signaling and adhesion have led to greatly increased interest and appreciation of this class of compounds. It is now recognized that
these complex biomolecules, in the form of glycoprotein and
glycolipid conjugates, carry detailed structural information,
which serves to mediate a variety of biological events including
inflammation,['] immunological response,[21and meta~tasis.[~]
Furthermore, cell-surface carbohydrates act as biological markers for various tumors.[41
Of the three major classes of biooligomers, polysaccharides
have proven to be the most difficult to synthesize. The synthesis
of structurally defined ~ligopeptides[~]
and oligonucleotides[61
has greatly benefited from assembly on polymer supports. In
most cases the preparation of peptides and oligonucleotides can
be carried out on automated synthesizers, which allow rapid
formation of the target compounds. To simplify the very laborintensive solution-phase synthesis of carbohydrates, considerable efforts have been directed toward developing strategies and
sequences for solid-phase synthesis.[71Recent advances have
demonstrated that methodologies useful for glycosidation in
solution can be applicable on a polymer support. Indeed, large,
biologically important oligosaccharides have been prepared by
solid-phase methods.[81
Glycals have proven to be effective building blocks for the
synthesis of increasingly complex oligosaccharides.[91The approach is applicable to the synthesis of both glycopeptides
and oligosaccharides on the solid support." O1 While significant
progress has been made, a generally applicable method for the
rapid assembly of oligosaccharides and glycopeptides by automated solid-phase synthesis strategies has not yet been developed.
A major limitation is the difficulty in characterizing the reaction products or intermediates as they evolve during the course
of the synthesis. Currently, it is necessary to cleave these products from the resin to investigate them by classical spectroscopic
methods (for example solution NMR and mass spectrometry).
This is time-consuming, expensive, and wasteful for multistep
syntheses. Full characterization of the products while they are
still hound to the resin would hold many advantages.
[*I
Dr. P. H. Seeberger, Dr. X. Beebe, Prof. S.J. Danishefsky
Laboratory for Bio-Organic Chemistry
Sloan-Kettering Institute for Cancer Research
Box 106, 1275 York Avenue, New York, NY 10021 (USA)
Fax: Int. code +(212)772-8691
e-mail: p-seeberger(a ski.mskcc.org
Further address: Department of Chemistry, COlUmbld Unicersity
Dr. G. D . Sukenick
N M R Analytical Core Facility
Sloan-Kettering Institute for Cancer Research. New York (USA)
Dr. S. Pochapsky
Bruker Instruments Inc., Billerica, MA (USA)
[**I This research was supported by the U . S. National Institutes of Health (grant
no. HL-25848). X. B. gratefully acknowledges the NIH for a postdoctoral
training grant (no. T32CA62948).
Anyew. Chem. In1 Ed. Enxl. 1997. 36. No. 5
'C)
VCH Erlagsg~.dlschafrmbH. D-69451 W>inheim, 1997
057O-(lR33,'97,'3605-04916 I 5 . 0 0 i .25 I/
491
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