Rapid Solid-Phase Syntheses of Conjugated Homooligomers and [AB] Alternating Block Cooligomers of Precise Length and Constitution

Article abstract of DOI:10.1021/jo991201s

A new iterative divergent/convergent solid-phase synthesis of precisely defined oligomers is described. The starting monomer is affixed to the solid support so that both ends are free for growth. The polymer-supported n-mer bearing α,ω,-terminal iodides i

Full text of DOI:10.1021/jo991201s

8898
J . Org. Chem. 1999, 64, 8898-8906
Ra p id Solid -P h a se Syn th eses of Con ju ga ted Hom ooligom er s a n d
[AB] Alter n a tin g Block Cooligom er s of P r ecise Len gth a n d
Con stitu tion
Shenlin Huang and J ames M. Tour*
Department of Chemistry and Biochemistry, University of South Carolina,
Columbia, South Carolina 29208 and Rice University, Department of Chemistry and Center for
Nanoscale Science and Technology, MS 222, 6100 Main Street, Houston, Texas 77005
Received J uly 27, 1999
A new iterative divergent/convergent solid-phase synthesis of precisely defined oligomers is
described. The starting monomer is affixed to the solid support so that both ends are free for growth.
The polymer-supported n-mer bearing R,ω-terminal iodides is divided into two portions. The smaller
portion is converted to the polymer-supported (n + 2)-mer by coupling an R,ω-dialkyne to the two
iodide ends. The larger portion is liberated from the polymer support and then coupled with the
polymer-supported portion to form a polymer-supported (3n + 2)-mer with new R,ω-terminal iodide
end groups. The process is then repeated. The solid-supported material thereby grows in two
directions, unlike the common approach of unidirectional growth. This polymer-supported strategy
serves as a pseudo high dilution system so that unwanted polymerization does not ensue. Therefore,
after each iteration, the oligomer length is more than tripled, making this a rapid growth
methodology for precise oligomer syntheses. The methodology is demonstrated by the synthesis of
a 17-mer oligo(1,4-phenylene ethynylene) of approximately 120 Å length in seven steps with an
overall 20% yield. This solid-supported divergent/convergent tripling protocol is also used for the
synthesis of an [AB] alternating block 23-mer containing oligo(1,4-phenylene ethynylene)s and oligo-
(2,5-thiophene ethynylene)s in an overall 21% yield. The length of the 23-mer is approximately
160 Å.
In tr od u ction
siderably simplified because time-consuming chromato-
graphic separations are limited; only washing with
appropriate solvents is needed in order to purify the
polymer-supported substrates. (2) The reactions can be
driven to completion using large amounts of reagents
which can then be easily recovered by filtration. (3) While
solution-phase oligomer syntheses require the functional
end groups to be orthogonally (selectively) protected and
deprotected before each length-growing reaction, solid-
supported chemistry can suppress unwanted reactions
by site isolation conditions, thereby minimizing protec-
tion/deprotection steps. (4) Solid phase synthesis is
amenable to automation and combinatorial chemistry. To
demonstrate the efficiency of solid-phase synthesis, we
and others previously developed an iterative divergent/
convergent method for preparing oligo(phenylene ethy-
nylene)s in which the molecular length was doubled after
each coupling reaction step.3b,d We report here the details
of a new solid-supported method for the preparation of
homooligomers and [AB] alternating block oligomers that
more than triples the molecular length with each itera-
tion and avoids the masking and unmasking steps
normally required for aryl iodides.3f
Large conjugated molecules of precise length and
constitution have attracted much attention recently.1
These compounds can serve as models for analogous bulk
polymers, and they can also be used for the construction
of nanoarchitectures such as molecular wires and mo-
lecular scale electronic devices.1,2 Two main methods exist
for the solution-phase synthesis of conjugated oligomers.
The stepwise approach features successive addition of
monofunctional monomer to the end of a growing chain,
while the iterative divergent/convergent approach doubles
the molecular length with each iteration.1,3 These two
methods both require chromatographic purification at
every growth stage. Conversely, solid-supported chem-
istry has several advantages for the synthesis of conju-
gated oligomers.3,4 (1) The reaction procedures are con-
* Address correspondence to J ames M. Tour at Rice University.
(1) Tour, J . M. Chem. Rev. 1996, 96, 537.
(2) (a) Zhou, C.; Deshpande, M. R.; Reed, M. A.; J ones, L., II.; Tour,
J . M. Appl. Phys. Lett. 1997, 71, 611. (b) Reinerth, W. A.; J ones, L.,
II.; Burgin, T. P.; Zhou, C.-W.; Muller, C. J .; Deshpande, M. R.; Reed,
M. A.; Tour, J . M. Nanotechnology 1998, 9, 246. (c) Tour, J . M.; Kozaki,
M.; Seminario, J . M. J . Am. Chem. Soc. 1998, 120, 8486. (d) Cygan,
M. T.; Dunbar, T. D.; Arnold, J . J .; Bumm, L. A.; Shedloch, N. F.;
Burgin, T. P.; J ones, L., II.; Allara, D. L.; Tour, J . M.; Weiss, P. S. J .
Am. Chem. Soc. 1998, 120, 2721.
(3) For routes to oligo(phenylene ethynylene)s, see (a) Zhang, J .;
Moore, J . S. Angew. Chem., Int. Ed. Engl. 1992, 31, 922. (b) Young, J .
K.; Nelson, J . C.; Moore, J . S. J . Am. Chem. Soc. 1994, 116, 10841. (c)
Golt, A.; Ziener, U. J . Org. Chem. 1997, 62, 6137. (d) J ones, L., II.;
Schumm, J . S.; Tour, J . M. J . Org. Chem. 1997, 62, 1388. (e) Schumm,
J . S.; Pearson, D. L.; Tour, J . M. Angew. Chem., Int. Ed. Engl. 1994,
33, 1360. (f) Huang, S.; Tour, J . M. J . Am. Chem. Soc. 1999, 121, 4908.
For routes to oligo(thiophene ethynylene)s, see: (g) Pearson, D. L.;
Tour, J . M. J . Org. Chem. 1997, 62, 1376. (h) Pearson, D. L.; Schumm,
J . S.; Tour, J . M. Macromolecules 1994, 27, 2348.
The tripling strategy is outlined in Figure 1. The
starting monomer is affixed to the solid support so that
(4) (a) Polymer-Supported Reactions in Organic Synthesis; Hodge,
P., Sherrington, D. C., Eds.; Wiley: New York, 1980. (b) Fru¨chtel, J .
S.; J ung, G. Angew. Chem., Int. Ed. Engl. 1996, 35, 17. (c) Hermkens,
P. H. H.; Ottenheijm, H. C. J .; Rees, D. Tetrahedron 1996, 52, 4527.
(d) Thompson, L. A.; Ellman, J . A. Chem. Rev. 1996, 96, 555. (e)
Malenfant, P. R. L.; Fre´chet, J . M. J . Chem. Commun. 1998, 2657. (f)
Hodge, P. Chem. Soc. Rev. 1997, 26, 417.
10.1021/jo991201s CCC: $18.00 © 1999 American Chemical Society
Published on Web 10/30/1999

Solid-Phase Syntheses of Conjugated Homooligomers
J . Org. Chem., Vol. 64, No. 24, 1999 8899
F igu r e 1. Schematic representation of the iterative divergent/convergent approach with (3n + 2) molecular growth.
F igu r e 2. Intramolecular hydroxyl addition to an unactivated carbon-carbon triple bond via 6-endo- or 5-exo-digonal pathways.
both ends are free for growth. The polymer supported
n-mer bearing R,ω-bis-terminal iodides is divided into two
portions. The smaller portion is converted to polymer-
supported (n + 2)-mer with 1,4-diethynylbenzene addi-
tion at the two iodide ends. The larger portion is liberated
from the polymer support and then coupled with the
polymer-supported portion to form a polymer-supported
(3n + 2)-mer with new R,ω-bis-terminal iodide end
groups. A functionalized insoluble polymer can provide
an environment of “high dilution” thereby retarding
polymerization that would be obtained by a solution-
phase process. Since the end groups in this polymer-
supported (3n + 2)-mer are the same as the polymer-
supported n-mer, the procedure can be repeated. The
solid supported material grows in two directions, unlike
the common approach of unidirectional growth. Each
iteration extends the chain by three times the original
length plus the length of two linker molecules.
ethynyl)benzene (2) (eq 2). The separation of monosilyl-
ated product, 2, from the disilylated side product was
difficult; however, this impurity had no effect on the
coupling reaction and was carried with 2 to the next step.
Finally, 2,5-didodecyl-1,4-diiodobenzene (3) was gener-
ated by dilithiation of 1,4-diiodobenzene, a displacement
reaction with dodecyl bromide, and finally iodination (eq
3).7
Resu lts a n d Discu ssion
Mon om er Syn th esis. The syntheses of the three
monomers were performed as shown in eqs 1-3. Nickel-
catalyzed cross-coupling of 4-pentenylmagnesium bro-
mide with 1,4-dichlorobenzene yielded 1,4-di(4′-pentenyl)-
benzene.5,6 Hydroboration and oxidation afforded the diol
that was subsequently protected as the diacetate. Elec-
trophilic iodination7 and deprotection yielded the desired
1,4-diiodo-2,5-di(5′-hydroxypentyl)benzene (1) (eq 1). The
long hydroxyalkyl moieties provide good solubility for the
longer oligomers. Additionally, shorter alkyl spacers can
result in intramolecular addition of the hydroxyl group
to the alkyne unit that is subsequently attached at the
iodide-bearing positions (Figure 2).8 Monosilylation of 1,4-
diethynylbenzene9 afforded 1-ethynyl-4-(trimethylsilyl-
Hom ooligom er Syn th esis. The new solid-phase it-
erative divergent/convergent synthetic approach is out-
lined in Scheme 1. 2-(Hydroxymethyl)-3,4-dihydro-2H-
pyran was converted to its sodium salt and then treated
with Merrifield’s resin (1.0 mequiv of Cl/g, 2% DVB cross-
linked, 200-400 mesh, Aldrich) in dimethylacetamide at
room temperature to afford the dihydropyran-modified
resin 4.10 Compound 1 was then attached to 4 through
the hydroxy group in the presence of acid to afford 5.10
The loading level of 1 in 5 was determined by cleaving
the alcohol from the resin employing PPTS in 1:1 n-bu-
tanol/1,2-dichloroethane at 80 °C.10 Compound 5 (0.48
mequiv of 1/g) was subjected to a Pd/Cu-catalyzed cross-
coupling11 with monomer 2 to afford the polymer-sup-
ported trimer 6 that was deprotected with tetra-n-
(5) Kraus, G. A.; Landgrebe, K. Synthesis 1984, 885.
(6) Kumada, M.; Tamao, K.; Sumitani, K. Org. Synth. 1978, 58, 127
(7) Suzuki, H.; Nakamura, K.; Goto, R. Bull. Chem. Soc. J pn. 1966,
39, 128.
(8) Weingarten, M. D.; Padwa, A. Tetrahedron Lett. 1995, 36, 4717.
(9) (a) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagihara, N.
Synthesis 1980, 627. (b) MacBride, J . A. H.; Wade, K. Synth. Commun.
1996, 26, 2309.
(10) Thompson, L. A.; Ellman, J . A. Tetrahedron Lett. 1994, 35, 9333.

8900 J . Org. Chem., Vol. 64, No. 24, 1999
Huang and Tour
Sch em e 1
butylammonium fluoride (TBAF) to produce polymer-
supported trimer 7. Attempts to generate 7 directly from
5 and 1,4-diethynylbenzene failed, possibly due to rapid
trace-oxygen-catalyzed homocoupling of 1,4-diethynyl-
benzene. Compound 7 was then cross-coupled with 3 (5-6
mol of 3 per mol of 7) to afford polymer-supported
pentamer 8. Excess 3 was easily recovered by filtration.
One portion of 8 was coupled with 2 to produce the
polymer-supported heptamer 9 that was desilylated to
afford polymer-supported heptamer 10. Another portion
of polymer-supported pentamer 8 was treated with acid
to liberate pentamer 11. Treatment of 10 with the
liberated pentamer 11 (6-8 mol of 11 per mol of 10)
under Pd/Cu cross-coupling conditions (23 °C for 24 h,
and then 60-70 °C for 24 h) afforded the polymer-
supported 17-mer 12. Directly heating the mixture of 10
and 11 caused a much lower yield, possibly due to
decomposition of the polymer-supported R,ω-diyne 10.
Recovery of excess 11 was achieved simply by filtration
from the beads followed by passage through silica gel.
Finally, treatment of 12 with acid liberated the 120 Å
long 17-mer 13.10 The overall yield was 20% for the seven-
step sequence from 5.
(11) (a) Suffert, J .; Ziessel, R. Tetrahedron Lett. 1991, 32, 757. (b)
Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975, 4467.
(c) Stephens, R. D.; Castro, C. E. J . Org. Chem. 1963, 28, 3313. (d)
For application of this reaction to poly[(1,4-phenylene ethynylene)-alt-
(2,5-thiophene ethynylene)]s, see: Li, J .; Pang, Y. Macromolecules
1998, 31, 5740.

Solid-Phase Syntheses of Conjugated Homooligomers
J . Org. Chem., Vol. 64, No. 24, 1999 8901
[AB] Alter n a tin g Block Cooligom er Syn th esis.
Block copolymers are fascinating materials exhibiting
interesting phase behaviors. They can self-assemble into
nanometer-scale multiphase domain structures as a
consequence of the compatibility restraints on the
blocks.12-14 On the basis of our experience with conju-
gated oligomers,1 we decided to use the aforementioned
solid-support methodology to prepare conjugated block
oligomers containing oligo(1,4-phenylene ethynylene)s
and oligo(2,5-thiophene ethynylene)s. Oligo(2,5-thiophene
ethynylene) 14 was synthesized as we described previ-
acid matrix in positive ion mode. MALDI-MS of 13
afforded a peak that was 254 amu lower than the actual
molecular weight of 13, corresponding to the molecular
ion minus the two iodides. MALDI-MS of 20 did afford
the desired M + 1 peak.
Size exclusion chromatography (SEC) was conducted
after benchtop chromatography on the obtained oligo-
mers.1,3 SEC is not a direct measure of molecular weight
but a measure of the hydrodynamic volume. Thus, the
number average molecular weight (Mn) values of rigid
rod oligomers should be significantly inflated relative to
the randomly coiled polystyrene standards. As expected,
the Mn values of the pentamer 11 (Mn ) 2200, PDI )
1.18, actual molecular weight ) 1576), 17-mer 13 (Mn )
8000, PDI ) 1.06, actual molecular weight ) 4468) and
23-mer 20 (Mn ) 12000, PDI ) 1.03, actual molecular
weight ) 5342) were much greater than the actual
molecular weights. Additionally, SEC on a crude reaction
mixture was used to determine whether polymerization
or oligomerization could ensue using this synthetic
protocol. The heptamer on 9 was cleaved from the
polymer support, and the crude material was analyzed.
As expected, the site isolation inhibited polymerization.
However, in addition to the expected heptamer derived
from 9 (Mn ) 2700, PDI ) 1.01), there was an equal area
broadened peak at slightly higher molecular weight
which likely arose from undesired oligomer formation.
This could have arisen from several intersite interactions
along the synthetic sequence, for example, coupling of 7
with 8 followed by capping with 2. Therefore, although
this technique inhibits polymer formation, the confor-
mational flexibility of Merrifield resin does not allow the
functionalized sites to be exclusively isolated from each
other. We may be able to overcome this problem in the
future using a lower degree of loading and a more rigid
matrix through higher DVB cross-link levels.4e Addition-
ally, although the final yields of the 17-mer 13 and 23-
mer 20 were relatively high for the size of the oligomers
formed, using a more suitable polymer support would
likely provide higher yields and higher purities of the
final products by permitting definitive site isolation.
Optical absorption (Figure 3) and emission (Figure 4)
spectra of the oligomers were recorded. As expected, we
observed an increase in the absorption maxima from
shorter wavelength (365 nm) for the pentamer 11 to
longer wavelength (385 nm) for the 17-mer 13. These
absorptions corresponded very closely to our oligo(1,4-
phenylene ethynylene)s prepared previously.3d The ab-
sorption maximum for the block 23-mer 20 was 390 nm
with a shoulder at 445 nm and a longer tail extending to
500 nm. The shoulder at 445 nm is characteristic of the
tetra(1,4-thiophene ethynylene) absorption tails.3g,11d Oligo-
(1,4-phenylene ethynylene)s 11 and 13 had an emission
maximum at 425 and 415 nm, respectively, thereby
indicating a larger Stokes shift for the pentamer. Oligo-
(2,5-thiophene ethynylene)s exhibit emission maximum
at 495 nm. As expected, the emission spectrum of the
block 23-mer 20 consisted of both oligo(phenylene ethy-
nylene) and oligo(thiophene ethynylene) characteristics.
ously.3g,h The two-directional solid-phase synthesis of
block oligomers is outlined in Scheme 2. Compound 8 was
coupled with (trimethylsilyl)acetylene to generate the
polymer-supported bis-terminal silyl pentamer 15.11 Des-
ilylation of 15 and cross-coupling with the thiophene-
containing tetramer 14 afforded the polymer-supported
triblock 13-mer 17. Desilylation of 17 and coupling with
the pentamer 11 gave the polymer-supported alternating
[AB] pentablock 23-mer 19. Treatment of 19 with acid
generated the desired block 23-mer 20.10 The yield was
21% over a total of nine reactions steps from 5 to afford
the 160 Å long system.
Sp ectr oscop ic Rea ction Mon itor in g Tech n iqu es
on t h e R esin . Completion of each polymer-supported
reaction step was determined by FTIR analysis of the
polymer bound substrate.3b,d,15 Polymer-supported mate-
rial was mixed with oven-dried KBr and ground to a
powder, and an FTIR spectrum was acquired from the
formed pellet. Absorptions at 3290 cm-1 (strong) and 2110
cm-1 (weak) are characteristic of the terminal alkynyl
carbon-hydrogen and carbon-carbon stretches, respec-
tively, and a strong absorption at 2150 cm-1 is charac-
teristic of the carbon-carbon stretch of the trimethylsilyl-
terminated alkyne. As expected, we observed that the
coupling reaction of a polymer-supported aryl diiodide
with 2 was accompanied by the appearance of the 2150
cm-1 absorption. The trimethylsilyl removal step was
confirmed by the appearance of the 3290 cm-1 band and
the diminution of the 2150 cm-1 band. The coupling
reaction of polymer-supported R,ω-dialkynes with aryl
diiodides was accompanied by the disappearance of the
3290 cm-1 band.3b,d,15
Ch a r a cter iza tion of th e Oligom er s. While the pen-
tamer 11 afforded a molecular ion peak by direct expo-
sure via electron impact mass spectrometry (MS), neither
this method nor FAB or electrospray MS sufficed to
obtain a molecular ion of the 17-mer 13 or the 23-mer
20. For these latter compounds, it was necessary to use
matrix-assisted laser desorption/ionization mass spec-
trometry (MALDI-MS) using R-cyano-4-hydroxycinnamic
(12) Quirk, R. P.; Kinning, D. J .; Fetters, L. J . In Comprehensive
Polymer Science; Aggarwal, S. L., Ed., Pergamon Press Inc: New York,
1989; Vol. 7, p 1.
All excitations were at the maxima for λabs
.
(13) Li, W.; Maddux, T.; Yu, L. Macromolecules 1990, 29, 7329.
(14) Mu¨llen, K.; Wegner, G. Adv. Mater. 1998, 10, 433.
(15) (a)Yan, B.; Kumaravel, G.; Anjaria, H.; Wu, A.; Petter, R. C.;
J ewell, C. F., J r.; Wareing, J . R. J . Org. Chem. 1995, 60, 5736. (b)
Grindley, T. B.; J ohnson, D. F.; Katritzky, A. R.; Keogh, H. J .;
Thirkettle, C.; Topsom, R. D. J . Chem. Soc., Perkin Trans. 2 1974, 3,
282.
Con clu sion
A highly efficient synthetic approach to precisely sized
conjugated homooligomers and block cooligomers has
been developed. Since molecular growth is bidirectional,

8902 J . Org. Chem., Vol. 64, No. 24, 1999
Huang and Tour

Solid-Phase Syntheses of Conjugated Homooligomers
J . Org. Chem., Vol. 64, No. 24, 1999 8903
reagents were obtained from FMC. (Trimethylsilyl)acetylene
was obtained from FAR Research Inc. Reagent grade diethyl
ether and tetrahydrofuran (THF) were distilled under nitrogen
from sodium benzophenone ketyl. Reagent grade dichlo-
romethane, diethylamine, and diisopropylamine were distilled
under nitrogen from CaH2. Bulk grade hexane was distilled
prior to use. Gravity column chromatography and flash chro-
matography were carried out on silica gel (230-400 mesh from
EM Science). Pd/Cu-catalyzed Pd/Cu-catalyzed couplings of
aryl halides with terminal alkynes were conducted according
to reported procedures.11 Oligomer purities were assessed by
their polydispersity indexes (Mw/Mn). If a compound has
previously been reported, a reference to that compound is
shown directly after the compound number in the title of the
synthetic procedure. The FTIR spectra of the polymer-sup-
ported compounds often showed significant overtone bands at
ca. 1945, 1870, and 1800 cm-1, and these have been recorded.
1,4-Di(4′-p en ten yl)ben zen e.6 A 500 mL three-necked flask
was equipped with a mechanical stirrer and a reflux condenser.
The flask was charged with magnesium turnings (24.31 g, 1.00
mol) and ether (200 mL). Approximately 5 mL of a solution of
5-bromo-1-pentene5 (74.52 g, 500.00 mmol) in 100 mL of
diethyl ether was added. The mixture was stirred at room
temperature, and within a few minutes, an exothermic reaction
occurred. The flask was immersed in an ice bath, and the
remaining ether solution was added dropwise over 1 h. After
addition was complete, the mixture was heated to reflux for
30 min and then cooled to room temperature. Another 500 mL
three-necked flask was equipped with a mechanical stirrer and
F igu r e 3. The UV/vis spectra (CH2Cl2) of pentamer 11, 17-
mer 13, and 23-mer 20.
a
reflux condenser. The second flask was charged with
dichloro[1,3-bis(diphenylphosphino)propane]nickel(II) (2.71 g,
5.00 mmol), 1,4-dichlorobenzene (14.70 g, 100.00 mmol), and
diethyl ether (150 mL), and the mixture was cooled in an ice
bath. The Grignard reagent prepared above was transferred
via cannula to the mixture. After addition, the mixture was
warmed to room temperature and stirred for 2 h and then
heated to reflux overnight. After cooling in an ice bath, the
mixture was slowly hydrolyzed with 250 mL of 2 N aqueous
hydrochloric acid. The organic layer was separated, and the
aqueous layer was extracted with diethyl ether. The combined
organic layers were dried over MgSO4. The solvent was
removed in vacuo, and the residue was purified by flash
chromatography (silica gel, hexane) to afford 8.13 g (38%) of
the desired compound as a colorless liquid. FTIR (neat) 3077,
3006, 2977, 2930, 2856, 1897, 1826, 1641, 1514, 1492, 1441,
1416, 1348, 1208, 1093, 1016, 991, 911, 832, 760 cm-1. 1H NMR
(300 MHz, CDCl3) δ 7.08 (s, 4 H), 5.81 (m, 2 H), 5.04 (dd, J )
17.5, 1.7 Hz, 2 H), 4.98 (dd, J ) 17.5, 1.5 Hz, 2 H), 2.58 (t, J
) 7.6 Hz, 4 H), 2.09 (q, J ) 6.9 Hz, 4 H), 1.72 (p, J ) 7.5 Hz,
4 H). 13C NMR (75 MHz, CDCl3) δ 139.78, 138.72, 128.40,
114.70, 34.98, 33.40, 30.75. HRMS calcd for C16H22: 214.1721.
Found: 214.1732.
F igu r e 4. The emission spectra (CH2Cl2) of pentamer 11, 17-
mer 13, and 23-mer 20.
the molecular length triples at each iteration. A 17-
membered homooligomer 13 and alternating block 23-
membered cooligomer 20 were prepared whose molecular
weights are in the range of many conjugated polymers.16
Using this solid-phase methodology, undesired polymer-
izations are not encountered through the pseudo high
dilution conditions. Additionally, with the approach
described here, masking and unmasking of the aryl
iodides were unnecessary. This solid-phase divergent/
convergent tripling protocol should find widespread use
in the synthesis of many precisely defined homo- and
block-oligomers.
1,4-Di(5′-h yd r oxyp en tyl)ben zen e. To a nitrogen-purged
flask was added 1,4-di(4′-pentenyl)benzene (8.5 g, 39.7 mmol)
and THF (100 mL). Borane-tetrahydrofuran complex solution
in tetrahydrofuran (158.8 mL, 158.8 mmol, 1.0 M) was added
dropwise. The mixture was heated to 50 °C for 3 h. After
cooling to 0 °C, ethanol (22 mL, 477 mmol) was slowly added,
and then 2 N aqueous NaOH (39.7 mL, 79.4 mmol) and 30%
H2O2 (45 mL, 397 mmol) were added sequentially. The mixture
was stirred at room-temperature overnight and then poured
into water and extracted with ethyl acetate. The combined
organic layers were dried over anhydrous MgSO4. The solvent
was removed in vacuo to afford 9.7 g (97%) of the desired
product as a colorless liquid. FTIR (neat) 3332, 3008, 2925,
1898, 1790, 1660, 1644, 1514, 1462, 1372, 1116, 1048, 960, 808
Exp er im en ta l Section
Gen er a l. All nonaqueous operations were carried out under
a dry, oxygen-free, nitrogen atmosphere. Molecular weight
analyses (SEC) were performed using two 30 × 75 cm GPC
columns (105 Å 10 µm and 500 Å 5 µm) eluted with THF at 60
°C (flow rate 1.0 mL/min). SEC results were based on six
polystyrene standards (Mw ) 135 500, 96 000, 52 000, 22 000,
5050, and 510 with a correlation coefficient > 0.9998) pur-
chased from Polymer Laboratories Ltd. Unless otherwise
noted, all starting materials were obtained from commercial
suppliers and used without further purification. Merrifield’s
resin was purchased from Aldrich Chemical Co. (1.0 mequiv
of Cl/g, 2% DVB cross-linked, 200-400 mesh). Alkyllithium
1
cm-1. H NMR (300 MHz, CDCl3) δ 7.07 (s, 4 H), 3.57 (t, J )
6.5 Hz, 4 H), 2.81 (br s, 2 H), 2.58 (t, J ) 7.6 Hz, 4 H), 1.60
(m, 8 H), 1.38 (m, 4 H). 13C NMR (75 MHz, CDCl3) δ 139.86,
128.32, 62.61, 35.54, 32.60, 31.40, 25.52. HRMS calcd for
C
16H26O2: 250.1933. Found: 250.1922.
1,4-Di(5′-a cetoxyp en tyl)ben zen e. To a nitrogen-purged
flask were added 1,4-di(5′-hydroxylpentyl)benzene (10.3 g, 41.2
mmol), pyridine (200 mL), and acetic anhydride (39 mL, 412
mmol). The mixture was stirred at room-temperature over-
(16) (a) Heitz, W. Polym. Prepr. (Am. Chem. Soc. Div. Polym. Chem.)
1991, 32(1), 327. (b) Solomin, V. A.; Heitz, W. Macromol. Chem. Phys.
1994, 195, 303.

8904 J . Org. Chem., Vol. 64, No. 24, 1999
Huang and Tour
night. The solvent was removed in vacuo to afford 13.8 g
(100%) of the desired product as a colorless liquid. FTIR (neat)
3644, 3458, 3048, 3007, 2934, 2858, 1901, 1732, 1514, 1463,
1386, 1366, 1236, 1118, 1044, 958, 896, 823, 730, 634, 606
39 °C. FTIR (KBr) 2918, 2850, 1897, 1656, 1516, 1467, 1384,
1121, 1020, 887, 823, 764, 721 cm-1 1H NMR (300 MHz,
.
CDCl3) δ 7.07 (s, 4 H), 2.55 (t, J ) 7.1 Hz, 4 H), 1.58 (br s, 4
H), 1.24 (br s, 36 H), 0.87 (t, J ) 5.8 Hz, 6 H). 13C NMR (75
MHz, CDCl3) δ 140.09, 128.22, 35.59, 31.94, 31.61, 29.69, 29.66,
29.62, 29.55, 29.42, 29.37, 22.71, 14.13. HRMS calcd for
1
cm-1. H NMR (300 MHz, CDCl3) δ 7.05 (s, 4 H), 4.02 (t, J )
6.8 Hz, 4 H), 2.56 (t, J ) 7.5 Hz, 4 H), 2.00 (s, 6 H), 1.60 (m,
8 H), 1.38 (m, 4 H). 13C NMR (75 MHz, CDCl3) δ 171.16,
139.69, 128.29, 64.48, 35.35, 31.12, 28.47, 25.57, 20.97. HRMS
calcd for C20H30O4: 334.2144. Found: 334.2142.
C
30H54: 414.4216. Found: 414.4226.
2,5-Did od ecyl-1,4-d iiod oben zen e (3).7 To a nitrogen-
purged flask were added water (10 mL), acetic acid (100 mL),
sulfuric acid (3 mL), carbon tetrachloride (20 mL), iodine (4.5
g, 17.6 mmol), periodic acid (2.0 g, 8.8 mmol), and 1,4-di-
(dodecyl)benzene (7.3 g, 17.6 mmol). The mixture was heated
to reflux overnight and then poured into water and extracted
with hexane. The combined organic layers were washed with
1 N aqueous Na2CO3 and 1 N aqueous Na2S2O3 and then dried
over MgSO4. The solvent was removed in vacuo. The residue
was washed with ethanol to afford 10.9 g (93%) of the desired
product as a white solid that was used without purification.
Mp ) 65-66 °C. FTIR (KBr) 2919, 2848, 1463, 1418, 1378,
1327, 1244, 1194, 1121, 1038, 939, 870, 777, 721 cm-1. 1H NMR
(300 MHz, CDCl3) δ 7.58 (s, 2 H), 2.58 (t, J ) 7.6 Hz, 4 H),
2,5-Di(acetoxypen tyl)-1,4-diiodoben zen e.7 To a nitrogen-
purged flask were added acetic acid (50 mL), water (10 mL),
sulfuric acid (1.5 mL), iodine (1.1 g, 4.4 mmol), periodic acid
(0.5 g, 2.2 mmol), and 1,4-di(5′-acetoxypentyl)benzene (1.5 g,
4.4 mmol). The mixture was heated to 80 °C for 3 h. The
solvent was then removed in vacuo. The residue was dissolved
in ethyl acetate and washed with water, 1 N aqueous K2CO3,
and 1 N aqueous Na2S2O3. After drying with anhydrous
MgSO4, the solvent was removed in vacuo, and the residue
was purified by flash chromatography (silica gel, CH2Cl2) to
afford 2.4 g (92%) of the desired product as a white solid. Mp
) 84-86 °C. FTIR (KBr) 2937, 2856, 1744, 1461, 1385, 1240,
1042, 956, 881 cm-1. H NMR (300 MHz, CDCl3) δ 7.55 (s, 2
1.53 (br s, 4 H), 1.26 (br s, 36 H), 0.88 (t, J ) 6.3 Hz, 6 H). 13
C
1
H), 4.03 (t, J ) 6.7 Hz, 4 H), 2.57 (t, J ) 7.4 Hz, 4 H), 2.01 (s,
6 H), 1.64 (p, J ) 7.6 Hz, 4 H), 1.54 (m, 4 H), 1.39 (m, 4 H).
13C NMR (75 MHz, CDCl3) δ 171.16, 144.52, 139.36, 100.32,
64.39, 39.63, 29.79, 28.39, 25.61, 21.07. HRMS calcd for
NMR (75 MHz, CDCl3) δ 144.85, 139.31, 100.37, 39.87, 31.96,
30.22, 29.72, 29.69, 29.60, 29.44, 29.39, 29.35, 22.73, 14.17.
HRMS calcd for C30H52I2: 666.2151. Found: 666.2159.
Dih yd r op yr a n -Mod ified Resin 4.10 To a nitrogen-purged
flask were added THF (100 mL), 2-(hydroxymethyl)-3,4-
dihydro-2H-pyran (6.84 g, 60.00 mmol), and 95% NaH (1.67
g, 66.10 mmol). The mixture was stirred at room temperature
for 2 h and then concentrated. To the residue were added
dimethylacetamide (300 mL) and Merrifield’s resin (20 g). The
mixture was stirred at room temperature for 16 h. The polymer
was then poured onto a preweighed fritted funnel using
dichloromethane to wash the beads that were adhering to the
sides of the flask. The beads were then washed sequentially
with CH2Cl2 (1×), 1:1 DMF/H2O (4×), DMF (3×), and CH2Cl2
(3×) and dried in a vacuum oven at 60 °C 12 h to afford 22.0
g of the dihydropyran functionalized resin. FTIR (KBr) 3025,
C
20H28O4I2: 586.0077. Found: 586.0072.
2,5-Di(5′-h yd r oxyp en tyl)-1,4-d iiod oben zen e (1). 1,4-Di-
iodo-2,5-di(5′-acetoxypentyl)benzene (1.5 g, 2.6 mmol) was
dissolved in dichloromethane (2 mL). Methanol (50 mL) and
potassium carbonate (3.6 g, 26.0 mmol) were added to the
solution. The mixture was stirred at room-temperature over-
night. The solvent was then removed in vacuo. The solid was
transferred into a fritted glass funnel and then washed with
water to afford 1.28 g (95%) the desired product as a white
solid. Mp ) 100-103 °C. FTIR (KBr) 3185, 2924, 2853, 1457,
1384, 1351, 1260, 1233, 1187, 1127, 1073, 1036, 990, 877, 787,
725, 686 cm-1. 1H NMR (300 MHz, CDCl3) δ 7.23 (s, 2 H), 3.65
(t, J ) 6.3 Hz, 4 H), 2.60 (t, J ) 7.6 Hz, 4 H), 1.58 (m, 8 H),
1.45 (m, 4 H), 1.23 (br s, 2 H). 13C NMR (75 MHz, CH3OD) δ
145.15, 139.72, 100.00, 61.97, 39.80, 32.48, 30.37, 25.69. HRMS
calcd for C16H24O2I2: 501.9866. Found: 501.9866.
1-E t h yn yl-4-(t r im et h ylsilylet h yn yl)b en zen e (2). To a
flame-dried and nitrogen-purged flask were added THF (200
mL) and 1,4-diethynylbenzene9 (2.0 g, 15.9 mmol). The mixture
was cooled to -78 °C, and n-BuLi (10.2 mL, 1.56 M in hexane)
was added via syringe pump over 1 h. After stirring at -78
°C for 2 h, trimethylsilyl chloride (3.0 mL, 23.9 mmol) was
added. The mixture was warmed to room temperature and
then stirred at room-temperature overnight. After concentra-
tion in vacuo, the residue was poured into water and extracted
with ether. The combined organic layers were dried over
anhydrous MgSO4. The solvent was removed in vacuo. The
residue was left on the vacuum pump (0.5 mmHg) for 12 h to
remove the unreacted 1,4-diethynylbenzene. The desired
product (3.14 g, 92%) was obtained which contained ∼5% of
the disilylated side product which did not participate in or
adversely affect the next reaction step. Mp ) 41-43 °C. FTIR
(KBr) 3295, 2960, 2899, 2159, 1495, 1403, 1251, 1222, 1103,
1018, 839, 760, 732, 700, 628 cm-1. 1H NMR (300 MHz, CDCl3)
δ 7.40 (s, 4 H), 3.15 (s, 1 H), 0.24 (s, 9 H). 13C NMR (CDCl3) δ
131.76, 131.67, 123.46, 121.99, 104.28, 96.39, 83.17, 78.93,
0.08. HRMS calcd for C13H14Si: 198.0865. Found: 198.0863.
1,4-Did od ecylben zen e. To a flame-dried and nitrogen-
purged flask were added 1,4-diiodobenzene (10.0 g, 30.3 mmol)
and THF (150 mL). The mixture was cooled to -78 °C, and
t-BuLi (75.8 mL, 1.60 M in pentane) was added dropwise. After
stirring at -78 °C for 1 h, 1-bromododecane (10.3 mL, 60.6
mmol) was added dropwise. The mixture was kept at -78 °C
for 1 h and then warmed to room temperature and stirred at
room temperature for 24 h. The mixture was poured into water
and extracted with hexane (3×). The combined organic layers
were dried over anhydrous MgSO4. The solvent was removed
in vacuo. The residue was recrystallized from ethanol to afford
11.5 g (92%) of the desired product as a white solid. Mp ) 37-
2920, 1601, 1492, 1450, 1384, 1069, 1027, 905, 756, 690 cm-1
.
P olym er -Su p p or ted Ar yl Diiod id e 5.10 Resin 4 (16.17 g,
15.00 mmol of the DHP moiety) was suspended in 1,2-
dichloroethane (350 mL). The aryl diiodide 1 (22.59 g, 45.00
mmol) and PPTS (7.53 g, 30.00 mmol) were added. The
mixture was stirred at 80 °C for 2 d. The polymer was then
poured onto a preweighed fritted funnel using dichloromethane
to wash the beads that were adhering to the sides of the flask.
The beads were then washed sequentially with CH2Cl2 (1×),
1:1 DMF/H2O (4×), DMF (3×), and CH2Cl2 (3×) and dried in
a vacuum oven at 60 °C overnight to afford 21.35 g of the
desired product. The loading level was 0.48 mequiv of 1 per
gram of polymer as determined by PPTS-induced cleavage
(vide infra) and recovery of 1. FTIR (KBr) 3448, 3025, 2924,
2854, 1600, 1493, 1451, 1384, 1251, 1073, 837, 757, 699 cm-1
.
Gen er a l P r oced u r e for th e Cou p lin g of a P olym er -
Su p p or t ed Ar yl Diiod id e w it h a n Alk yn e (P r oced u r e
A).11 A heavy-walled, oven-dried flask was charged with the
polymer-supported aryl diiodide, the alkyne, bis(dibenzylide-
neacetone)palladium(0) (10 mol % based on the diiodide),
copper(I) iodide (10 mol % based on the diiodide), triphen-
ylphosphine (20 mol % based on the diiodide), and diethyl-
amine/THF (1:4) (10 mL/g of polymer). The flask was flushed
with nitrogen and kept at 70 °C for 24 h with stirring. The
polymer was then poured onto a preweighed fritted funnel
using dichloromethane to wash the beads that were adhering
to the sides of the flask. The beads were then washed
sequentially (ca. 30 mL/g of polymer) with the following: CH2-
Cl2, DMF, 0.05 M solution of sodium diethyl dithiocarbamate
in 99:1 DMF/diisopropylethylamine, DMF, CH2Cl2, MeOH, and
dried to constant mass in a vacuum oven at 60 °C.
P olym er -Su p p or ted Bis(ter m in a l silyl) Tr im er 6. See
procedure A. 5 (10.0 g), 2 (2.19 g, 11.04 mmol), bis(dibenzylide-
neacetone)palladium(0) (0.26 g, 0.46 mmol), copper(I) iodide
(0.087 g, 0.46 mmol), triphenylphosphine (0.24 g, 0.92 mmol),
diethylamine (20 mL), and THF (80 mL) afforded 10.5 g of
the title polymer as yellow beads. FTIR (KBr) 3454, 3059,

Solid-Phase Syntheses of Conjugated Homooligomers
3026, 2923, 2854, 2154, 1944, 1873, 1802, 1657, 1600, 1493,
J . Org. Chem., Vol. 64, No. 24, 1999 8905
830, 723 cm-1. 1H NMR (300 MHz, CDCl3) δ 7.66 (s, 2 H), 7.48
(s, 8 H), 7.36 (s, 2 H), 7.29 (s, 2 H), 3.64 (t, J ) 6.6 Hz, 4 H),
2.82 (t, J ) 7.7, 4 H), 2.72 (t, J ) 7.6, 4 H), 2.62 (t, J ) 7.7, 4
H), 1.75 (p, J ) 7.3 Hz, 4 H), 1.65-1.41 (m, 12 H), 1.24 (m, 76
H), 0.86 (t, J ) 7.0 Hz, 6 H), 0.85 (t, J ) 7.0 Hz, 6 H). 13C
NMR (75 MHz, CDCl3) δ 144.12, 142.84, 142.05, 139.54,
132.46, 132.25, 131.44, 123.34, 123.19, 122.61, 122.47, 101.26,
93.97, 93.16, 90.26, 89.91, 62.89, 40.24, 34.06, 33.86, 32.67,
31.96, 30.66, 30.36, 30.24, 29.70, 29.52, 29.39, 25.63, 22.72,
14.15. SEC (THF): Mn ) 2200, Mw ) 2600, Mw/Mn ) 1.18. λabs
(CH2Cl2) 365 nm, ꢀ (THF) ) 9.6 × 104. λemis (CH2Cl2, excitation
at 365 nm) 425 nm. LRMS (EI) calcd for C96H136I2O6: 1576.
Found: 1576.
1448, 1384, 1251, 1114, 1029, 840, 755, 696 cm-1
.
Gen er a l P r oced u r e for th e Desilyla tion of a P olym er -
Su p p or ted Silyla ted Alk yn e (P r oced u r e B). To a suspen-
sion of polymer-supported arylbis(trimethylsilyl)alkyne and
THF (10 mL/g of polymer) in a heavy-walled, oven-dried flask
was added a solution of TBAF (1.0 M in THF). The suspension
was swirled periodically for 30 min. The polymer was then
transferred to a preweighed fritted funnel using THF, washed
sequentially (ca. 30 mL/g polymer) with THF, MeOH, CH2-
Cl2, and MeOH, and dried to constant mass in a vacuum oven
at 60 °C.
P olym er -Su p p or ted Bis(ter m in a l a lk yn yl) Tr im er 7.
See procedure B. 6 (10.5 g), THF (100 mL), and TBAF (18.4
mL, 18.4 mmol, 1.0 M in THF) afforded 10.3 g of the title
polymer as yellow beads. FTIR (KBr) 3451, 3287, 3059, 3025,
2922, 2854, 1944, 1802, 1656, 1600, 1492, 1449, 1383, 1071,
P olym er -Su p p or ted Bis(ter m in a l iod o) 17-m er 12. See
procedure C. 10 (0.98 g), 11 (1.25 g, 0.79 mmol), bis(diben-
zylideneacetone)palladium(0) (18.98 mg, 0.033 mmol), copper-
(I) iodide (6.27 mg, 0.033 mmol), triphenylphosphine (17.29
mg, 0.066 mmol), diethylamine (2 mL), and THF (8 mL)
afforded 1.30 g of the title polymer as yellow beads. FTIR (KBr)
3449, 3059, 3024, 2921, 2854, 2201, 1802, 1736, 1655, 1598,
1029, 901, 837, 756, 697 cm-1
.
Gen er a l P r oced u r e for th e Cou p lin g of a P olym er -
Su p p or ted Bis(ter m in a l a lk yn e) w ith a n Ar yl Diiod id e
(P r oced u r e C).11 A thick-walled, oven-dried flask was charged
with the polymer-supported bis-terminal alkyne, the aryl
diiodide, bis(dibenzylideneacetone)palladium(0) (10 mol % per
diiodide), copper(I) iodide (10 mol % per diiodide), triphen-
ylphosphine (20 mol % per diiodide), and diethylamine/THF
(1:4) (10 mL/g of polymer). The flask was flushed with nitrogen
and kept at room temperature for 24 h with stirring and then
heated to 60 ˚C for 24 h. The polymer was then poured onto a
preweighed fritted funnel using dichloromethane to wash the
beads that were sticking to the sides of the flask. The beads
were then washed sequentially (ca. 30 mL/g of polymer) with
the following: CH2Cl2, DMF, 0.05 M solution of sodium diethyl
dithiocarbamate in 99:1 DMF/diisopropylethylamine, DMF,
CH2Cl2, MeOH, and dried to constant mass in a vacuum oven
at 60 °C.
1491, 1448, 1384, 1237, 1069, 1026, 896, 833, 753, 696 cm-1
.
Bis(ter m in a l iod o) 17-m er 13. See procedure D. 12 (1.30
g), PPTS (0.17 g, 0.66 mmol), 1,2-dichloroethane (5 mL), and
n-butanol (5 mL) afforded 0.31 g (20% after seven steps)17 of
the title compound as a yellow solid after flash chromatogra-
phy (CH2Cl2/THF 9:1). FTIR (KBr) 3418, 2924, 2854, 1727,
1601, 1514, 1463, 1378, 1273, 1177, 1121, 1071, 894, 833, 721,
694 cm-1. H NMR (400 MHz, CDCl3) δ 7.62 (s, 2 H), 7.49 (br
1
s, 34 H), 7.36 (br s, 14 H), 3.65 (br t, J ) 6.4 Hz, 12 H), 2.81
(m, 36 H), 1.8-1.2 (m, 282 H), 0.85 (m, 36 H). 13C NMR (100
MHz, CDCl3) δ 142.19, 141.87, 139.38, 132.32, 132.25, 131.29,
123.00, 122.46, 94.22, 93.97, 93.81, 93.72, 90.48, 90.40, 90.28,
90.21, 64.20, 34.25, 34.15, 32.77, 32.04, 30.78, 30.45, 29.81,
29.78, 29.75, 29.67, 29.48, 25.73, 22.82, 14.27. SEC (THF) Mn
) 8000, Mw ) 8500, Mw/Mn ) 1.06. (The initial polydispersity
index was 1.2, and all spectra were recorded at that purity
level. Preparative TLC on a portion was used to sharpen the
index to 1.06.) λabs (CH2Cl2) 385 nm, ꢀ (THF) ) 1.1 × 105. λemis
(CH2Cl2, excitation at 385 nm) 415 nm. MALDI-MS (R-cyano-
4-hydroxycinnamic acid matrix in positive ion mode) calcd for
P olym er -Su p p or t ed Bis(t er m in a l iod o) P en t a m er 8.
See procedure C. 7 (10.3 g), 3 (7.36 g, 11.04 mmol), bis-
(dibenzylideneacetone)palladium(0) (0.26 g, 0.46 mmol), cop-
per(I) iodide (0.087 g, 0.46 mmol), triphenylphosphine (0.24
g, 0.92 mmol), diethylamine (20 mL), and THF (80 mL)
afforded 13.9 g of the title polymer as yellow beads. FTIR (KBr)
3450, 3058, 3024, 2920, 2853, 2341, 2206, 1944, 1802, 1656,
1599, 1490, 1448, 1384, 1264, 1068, 1028, 899, 833, 754, 696
C
308H416I2O6: 4468.5. Found: 4215 ( 10 (loss of two iodides).
P olym er -Su p p or ted Bis(ter m in a l silyl) P en ta m er 15.
See procedure A. Polymer-supported bis-terminal iodo pen-
tamer 8 (2.00 g), (trimethylsilyl)acetylene (0.27 mL, 1.89
mmol), bis(dibenzylideneacetone)palladium(0) (34.5 mg, 0.06
mmol), copper(I) iodide (11.4 mg, 0.06 mmol), triphenylphos-
phine (31.44 mg, 0.12 mmol), diethylamine (10 mL), and THF
(20 mL) afforded 2.05 g of the title polymer as yellow beads.
FTIR (KBr) 3450, 3059, 3026, 2921, 2852, 2148, 1944, 1872,
1802, 1678, 1600, 1491, 1448, 1381, 1250, 1115, 1070, 1027,
cm-1
.
P olym er -Su p p or t ed Bis(t er m in a l silyl) Hep t a m er 9.
See procedure A. 8 (1.00 g), 2 (0.16 g, 0.79 mmol), bis-
(dibenzylideneacetone)palladium(0) (18.98 mg, 0.033 mmol),
copper(I) iodide (6.27 mg, 0.033 mmol), triphenylphosphine
(17.29 mg, 0.066 mmol), diethylamine (2 mL), and THF (8 mL)
afforded 1.03 g of the title polymer as yellow beads. FTIR (KBr)
3425, 3058, 3025, 2922, 2853, 2154, 1655, 1600, 1543, 1515,
837, 754, 694, 600 cm-1
.
1492, 1450, 1384, 1250, 1106, 1031, 838, 757, 698 cm-1
.
P olym er -Su p p or ted Bis(ter m in a l a lk yn yl) P en ta m er
16. See procedure B. Polymer-supported bis-terminal silyl
pentamer 15 (2.05 g), THF (20 mL), and TBAF (2.52 mL, 2.52
mmol, 1.0 M in THF) afforded 1.98 g of the title polymer as
P olym er -Su p p or ted Bis(ter m in a l a lk yn yl) Hep ta m er
10. See procedure B. 9 (1.03 g), THF (10 mL), and TBAF (1.32
mL, 1.32 mmol, 1.0 M in THF) afforded 0.98 g of the title
polymer as yellow beads. FTIR (KBr) 3468, 3289, 3025, 2918,
2206, 1943, 1800, 1656, 1599, 1491, 1446, 1382, 1265, 1068,
(17) The overall yields of the final 17-mer 13 and the 23-mer 20
were determined by comparing the loading of the monomer 1 on the
polymer support (compound 5) and the yield of the final oligomer when
liberated from the polymer support. The loading level of the starting
material 1 on the polymer support, compound 5, was determined by
cleavage of 1 from 5 using the acidic conditions described. Each
synthetic process then started with 5 (10.0 g, 4.8 mmol of loading of
1). The sequence followed for the 17-mer 13 is as follows: 5 (10.0 g,
4.8 mmol of loading of 1) f 6 (10.5 g) f 7 (10.3 g) f 8 (13.9 g) of
which only a 7.2% mass portion (1.00 g) was taken on in the polymer
supported form f 9 (1.03 g) f 10 (0.98 g) f 12 (1.30 g) f 13 (0.31 g,
0.069 mmol). Starting from 4.8 mmol of 1 in 5 and using only 7.2%
mass of the material during the conversion of 8 f 9, gives a theoretical
yield of 0.35 mmol and an actual yield of 20% for 13. The sequence
followed for the 23-mer 20 is as follows: 8 (13.9 g, from above) of which
only a 14.4% mass portion (2.00 g) was used for the next step f 15
(2.05 g) f 16 (1.98 g) f 17 (2.50 g) of which only a 15.9% mass portion
(0.40 g) was used for the next step f 18 (0.39 g) f 19 (0.60 g) f 20
(0.124 g, 0.023 mmol). Starting from 4.8 mmol of 1 in 5 and using only
14.4% of the material in the conversion of 8 f 15, and only a 15.9%
portion in the conversion of 17 f 18, gives a theoretical yield of 0.11
mmol and an actual yield of 21% for 20.
1026, 898, 833, 751, 693, 537, 440, 407 cm-1
.
Gen er a l P r oced u r e for th e Liber a tion of P olym er -
Su p p or ted Oligom er s (P r oced u r e D). A heavy-walled,
oven-dried flask was charged with a suspension of the polymer-
supported oligomer and 1:1 n-butanol/1,2-dichloroethane. PPTS
was added. The flask was flushed with nitrogen and heated
to 80 °C for 16 h. The reaction mixture was cooled and passed
through a fritted funnel. The resin was washed with dichlo-
romethane to remove any residual product trapped in the
polymer matrix. The combined filtrate was washed with water
and then concentrated in vacuo. The residue was purified by
flash chromatography (silica gel). Eluents are described below
for each reaction.
Bis(ter m in a l iod o) P en ta m er 11. See procedure D. 8 (6.0
g), PPTS (0.95 g, 3.78 mmol), 1,2-dichloroethane (20 mL), and
n-butanol (20 mL) afforded 1.62 g of the title compound as a
yellow solid after flash chromatography (CH2Cl2). FTIR (KBr)
3356, 2920, 2848, 1512, 1464, 1377, 1185, 1100, 1056, 957, 885,

8906 J . Org. Chem., Vol. 64, No. 24, 1999
Huang and Tour
yellow beads. FTIR (KBr) 3429, 3297, 3025, 2923, 2853, 1945,
1803, 1600, 1492, 1450, 1382, 1214, 1115, 1070, 1029, 899, 836,
0.2 mmol), 1,2-dichloroethane (20 mL), and n-butanol (20 mL)
afforded 0.124 g (21% over nine steps)17 of the title compound
as a yellow solid after flash chromatography (CH2Cl2/THF 9:1).
FTIR (KBr) 3378, 2924, 2853, 2200, 1728, 1601, 1512, 1461,
755, 697 cm-1
.
P olym er -Su p p or ted Bis(ter m in a l silyl) 13-m er 17. See
procedure C. Polymer-supported bis-terminal alkynyl pen-
tamer 16 (1.98 g), iodinated tetramer 143g (1.39 g, 1.89 mmol),
bis(dibenzylideneacetone)palladium(0) (34.5 mg, 0.06 mmol),
copper(I) iodide (11.4 mg, 0.06 mmol), triphenylphosphine
(31.44 mg, 0.12 mmol), diethylamine (10 mL), and THF (20
mL) afforded 2.5 g of the title polymer as yellow beads. FTIR
(KBr) 3449, 3059, 3025, 2924, 2852, 2139, 1457, 1385, 1249,
1405, 1377, 1271, 1186, 1122, 1070, 895, 835, 721 cm-1 1H
.
NMR (500 MHz, CDCl3) δ 7.70 (s, 2 H), 7.51 (m, 24 H), 7.38
(m 16 H), 7.08 (m, 8 H), 3.67 (br t, J ) 8 Hz, 12 H), 2.75 (m,
52 H), 1.65-1.25 (m, 306 H), 0.86 (br t, J ) 8 Hz, 36 H). 13C
NMR (125 MHz, CDCl3) δ 143.19, 142.88, 133 (br), 132.9 (br),
132.3 (br), 132.29, 124 (br), 123.44, 95 (br), 63.95, 35 (br), 33.77,
33.04, 31.8 (br), 31.5 (br), 30.81, 30.66, 30.49, 26.73, 24.12,
1120, 1029, 902, 865, 837, 755, 697, 600 cm-1
.
23.84, 15.82, 15.66, 15.29. SEC (THF) Mn ) 12000, Mw )
P olym er -Su p p or ted Bis(ter m in a l a lk yn yl) 13-m er 18.
To a suspension of polymer-supported bis-terminal silyl 13-
mer 17 (0.40 g) and CH2Cl2 (10 mL) in a thick-walled oven-
dried flask were added K2CO3 (0.14 g, 1.00 mmol) and MeOH
(10 mL). The suspension was stirred at room temperature for
24 h. The polymer was then transferred to a preweighed fritted
funnel using THF, washed sequentially with THF (3×), MeOH
(3×), CH2Cl2 (3×), and MeOH (3×), and dried in a vacuum
oven at 60 °C to afford 0.39 g of the title polymer as yellow
beads. FTIR (KBr) 3450, 3299, 3025, 2920, 2854, 1944, 1802,
1656, 1597, 1493, 1448, 1383, 1262, 1070, 1025, 897, 836, 751,
12350, Mw/Mn ) 1.03. (The initial polydispersity index was 1.2,
and all spectra were recorded at that purity level. Preparative
TLC on a portion was used to sharpen the index to 1.03.) λabs
(CH2Cl2) 390, 445 (sh) nm, ꢀ (THF) ) 1.8 × 104. λemis (CH2Cl2,
excitation at 390 nm) 415, 495 nm. MALDI-MS (R-cyano-4-
hydroxycinnamic acid matrix in positive ion mode) calcd for
C
356H456I2O6S8: 5342. Found: 5349 (10, 5221 ( 10 (loss of
iodide).
Ack n ow led gm en t. Financial support from the Of-
fice of Naval Research and the Defense Advanced
Research Projects Agency is acknowledged. We thank
Dr. I Chester of FAR Research Inc. for a gift of
(trimethylsilyl)acetylene, FMC for providing the alkyl-
lithium reagent, and Professor Uwe Bunz for helpful
suggestions.
692 cm-1
.
P olym er -Su p p or ted Bis(ter m in a l iod o) 23-m er 19. See
procedure C. Polymer-supported bis-terminal alkynyl 13-mer
18 (0.39 g), bis-terminal iodo pentamer 11 (0.47 g, 0.30 mmol),
bis(dibenzylideneacetone)palladium(0) (5.7 mg, 0.01 mmol),
copper(I) iodide (1.9 mg, 0.01 mmol), triphenylphosphine (2.6
mg, 0.01 mmol), diethylamine (10 mL) and THF (20 mL)
afforded 0.60 g of the title polymer as yellow beads. FTIR (KBr)
3449, 3059, 3025, 2920, 2851, 1802, 1656, 1599, 1491, 1449,
Su p p or tin g In for m a tion Ava ila ble: Copies of spectral
and MS data for the compounds reported here. This material
is available free of charge via the Internet at http://pubs.acs.org.
1384, 1263, 1069, 1027, 896, 835, 753, 696 cm-1
.
Bis(ter m in a l iod o) 23-m er 20. See procedure D. Polymer-
supported bis-terminal iodo 23-mer 19 (0.6 g), PPTS (0.5 g,
J O991201S