Accoutrements of a molecular computer: Switches, memory components and alligator clips

Article abstract of DOI:10.1016/S0040-4020(01)00361-1

Several second generation memory components consisting of oligo(phenylene ethynylene)s containing easily reducible functionalities consisting of either nitro or quinone cores have been synthesized for incorporation into molecular electronic devices. Addit

Full text of DOI:10.1016/S0040-4020(01)00361-1

TETRAHEDRON
Pergamon
Tetrahedron 57 .2001) 5109±5121
Accoutrements of a molecular computer: switches, memory
components and alligator clips
Shawn M. Dirk, David W. Price, Jr., Stephanie Chanteau, Dmitry V. Kosynkin and James M. Tourp
Department of Chemistry and Center for Nanoscale Science and Technology, MS 222, Rice University, P.O. Box 1892, 6100 Main Street,
Houston, TX 77251-1892, USA
Dedicated to Professor Barry M. Trost on the occasion of his 60th birthday
Received 1 February 2001; revised 14 March 2001; accepted 15 March 2001
AbstractÐSeveral second generation memory components consisting of oligo.phenylene ethynylene)s containing easily reducible
functionalities consisting of either nitro or quinone cores have been synthesized for incorporation into molecular electronic devices.
Additionally, two new types of contacts between organic compounds and a metal surface based on diazonium salts or pyridine have been
synthesized and integrated into molecules for use in molecular electronic devices. q 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
2. Switches and memory components
Recent advances in the ®eld of molecular electronics have
shown that oligo.phenylene ethynylene)s containing nitro
groups are good candidates for electronic switching and
storage devices.1 Since the mechanism of switching and
electron storage involves a reduction upon applying a
potential,2 the search continues for a second generation of
storage and switching devices containing reversibly
reducible functional groups. To this end, two polynitro
compounds as well as several quinone derivatives have
been synthesized. Quinones are frequently found in nature
as electron acceptors and can be easily reduced and re-
oxidized, thus making them ideal for study in molecular
electronic devices.3,4
In an effort to improve the electron storage time by adding
more nitro groups, synthetic targets 1 and 2 were chosen.
The synthesis of compound 1 is outlined in Scheme 1.
In order to make molecular electronic components an
alternative to the presently utilized silicon analogs will
demand reliable low energy contacts between molecules
and conductive leads. Typically, this is accomplished via
a thiol group, which connects the active molecule to a
metal contact forming a well-ordered self-assembled mono-
layer .SAM).5 In an attempt to improve on the presently
used thiol alligator clip, we utilized the well-established
reactivity of aromatic diazonium salts toward transition
metals6 to produce a direct connection of the organic
molecules to metal surfaces through a carbon±metal
bond.7 We have also built on early work showing that
pyridine can assemble on a metal surface8 by synthesizing
molecules containing pyridine alligator clips.9
The synthesis of 1 began by Sonogashira coupling10 2,5-
dibromo-4-nitroaniline11 .3) to phenylacetylene affording
4, which was subjected to an HOF oxidation12 forming 5.
A ®nal coupling produced desired compound 1 in 24%
yield. The low yield in this coupling may be indicative of
the easily deprotected thiol or a stable palladacycle inter-
mediate that formed during coupling.
In order to conduct electrons all the phenyl rings in the
conjugated molecule should be preferentially planar to
each other.13 If a phenyl group replaces the terminal phenyl-
ethynyl group, the system cannot attain planarity. In an
effort to determine the effect of a rotational barrier .i.e.
conduction barrier), the synthesis of compound 2 was
initiated via a Suzuki14 coupling of 2,5-dibromo-4-nitro-
Keywords: diazonium; self-assembled monolayer; molecular computer;
quinones; memory components; switches.
p
Corresponding author. Tel.: 11-713-348-6246; fax: 11-713-348-6250;
e-mail: tour@rice.edu
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020.01)00361-1

5110
S. M. Dirk et al. / Tetrahedron 57 22001) 5109±5121
Scheme 1.
acetanilide .6)11 to phenylboronic acid to form compound 7.
The acetyl group was removed to provide the aniline .8)
functionality that would subsequently undergo an HOF
oxidation to afford 9 in nearly quantitative yield. A ®nal
Sonogashira coupling provided 2 .Scheme 2).
1,4-dimethoxybenzene .10). 10 was converted to 11 using
bromine and glacial acetic acid in good yield.16 Compound
11 was then cross-coupled with an excess of phenyl-
acetylene to afford compound 12, which was then oxidized
to the quinone affording desired compound 13. This
synthetic route had to be used because quinones generally
cannot be used in the palladium-catalyzed couplings since
quinones are known to oxidize palladium.0) to
palladium.II), terminating the catalytic cycle.17 Ceric
13 was synthesized for the purpose of studying the electro-
chemical properties of the quinone-containing molecular
system.15 Scheme 3 shows the synthesis of 13 from
Scheme 2.
Scheme 3.

S. M. Dirk et al. / Tetrahedron 57 22001) 5109±5121
5111
Scheme 4.
ammonium nitrate .CAN) is a mild and neutral oxidizing
agent known to generate quinones from dimethoxybenzenes
and therefore was a logical choice for this procedure.18 This
oxidation afforded the desired quinone compound in 47%
yield. The optimum conditions for the oxidation have not
yet been obtained for these systems.
®nal compound 17 was obtained in 74% yield via the CAN
oxidation.18 However, this yield was an isolated incident.
Other attempts resulted in much lower yields .,20%). More
work is underway to optimize the conditions of this CAN
oxidation.
Scheme 5 shows the synthesis of the quinone-containing
molecular system with alligator clips on both ends .5).
This compound can be used to crosslink metallic nano-
particles for bridging connections in future molecular
electronic devices. 11 was cross-coupled with an excess
of trimethylsilylacetylene followed by a subsequent
deprotection to cleanly afforded the diyne 18. This
was subsequently cross-coupled with 2 equiv. of 4-iodo-
benzenethioacetate to afford compound 19. Finally, 19
was oxidized using the CAN procedure to generate 20 in
modest yield.
Scheme 4 shows the synthesis of the quinone-containing
molecular system with one thioacetate group serving as a
protected alligator clip. Cross-coupling of 11 with phenyl-
acetylene afforded 14 in a modest yet statistically expected
yield of 33% due to the equal reactivity of both aryl
bromides of 11 under Sonogashira coupling conditions. 15
was prepared by the cross-coupling10 of trimethylsilyl-
acetylene with 14 followed by deprotection of the alkyne
to afford 15. Further palladium-catalyzed cross-coupling
with 4-iodobenzenethioacetate afforded compound 16. The
Scheme 5.

5112
S. M. Dirk et al. / Tetrahedron 57 22001) 5109±5121
3. Alligator clips
began by coupling one equivalent of 21 to 2,5-dibromo-
nitrobenzene selectively to the position ortho to the nitro
group affording 23. Coupling 23 to phenylacetylene to
produce 24 completed the synthesis.
The synthesis of several compounds containing a pyridine
alligator clip for incorporation into a molecular electronic
device began with compound 21. The synthesis of 22 was
accomplished by coupling pyridine 2119 with 2,5-dibromo-
nitrobenzene as shown in Eq. .1). The low yield may be due
to a stable copper acetylide formed after the TMS group is
cleaved. If an in situ deprotection was not used, the pyridine
alkyne proved to be unstable.
The synthesis of compound 26 was initiated to study the effect
of the nitro group in relation to the chemisorbed pyridine
alligator clip. To this end, compound 24 was synthesized in
a manor analogous to the synthesis of 23, as shown in Scheme
7. Coupling one equivalent of phenylacetylene selectively to
2,5-dibromonitrobenzene to produce 25 then coupling to 21 to
afford 26 in good yield completed the synthesis.
Linker 28 was synthesized according to Scheme 8. The
synthesis commenced with the coupling of 2,5-dibromo-4-
nitroacetanilide11 with excess trimethylsilylacetylene to
give 27, which was then deprotected in situ and coupled
with 4-iodopyridine to produce 28 in poor yield. The low
yield of the coupling reactions could be due to the
cyclization process reported by Rosen et al.20 between the
nitro and the alkyne unit.
ꢀ1†
24 was synthesized according to Scheme 6. The synthesis
Scheme 6.
Scheme 7.
Scheme 8.

S. M. Dirk et al. / Tetrahedron 57 22001) 5109±5121
5113
Scheme 9.
Compound 31 was synthesized in an effort to form an SAM
via the protected benzenethiol terminal group enabling the
pyridyl end of the molecule to serve as a better top contact
with metal than a phenyl when incorporated into a device.
31 was synthesized by coupling the 2,5-dibromo-4-nitro-
acetanilide11 with 21 in a low yield to afford compound
29. 29 was then coupled with trimethylsilylacetylene,
followed by deprotection with potassium carbonate to
yield 30. Finally, 30 was coupled with 4-iodobenzenethio-
acetate, which afforded the molecular device 31 in good
yield .75%) .Scheme 9).
.NDR) in a device embodiment.1
ꢀ3†
32 was synthesized to study the effect of a rotational barrier
analogous to that described for 2. The synthesis of 32 began
with previously synthesized 7 and coupling to 21 in good
yield, as shown in Eq. .2).
In addition to the pyridine-containing systems, three
potential memory and switching components terminated
by diazonium salts were synthesized. 38 is analogous to
the thioacetyl terminated NDR and memory component1
and the pyridyl terminated 24. The synthesis of 38 began
by coupling 357 to 2,5-dibromonitrobenzene in moderate
yield to afford 36, which was then coupled to phenyl-
acetylene to produce compound 37. Diazotization of 37
produced the completed molecule 38 in good yield .Scheme
10).
ꢀ2†
40 is similar in structure to 26 except the pyridyl group has
been replaced with the aryl diazonium salt. The synthesis of
40 is shown is Scheme 11. Coupling aniline 35 to nitro-
compound 25 produced diazonium precursor 39 in moderate
yield. Diazotization of aniline 42 afforded desired product
37.
Compound 34 was synthesized according to Eq. .3)
using the previously described 33. Compound 34 is
analogous to
previously exhibited negative differential resistance
a
thiol terminated nitroaniline that
Scheme 10.

5114
S. M. Dirk et al. / Tetrahedron 57 22001) 5109±5121
nitrogen atmosphere. Bulk hexanes were distilled prior to
use. Gravity column chromatography and ¯ash chromato-
graphy were carried out using 230±400 mesh silica gel from
EM Science. Thin layer chromatography .TLC) was
performed using Merck 40 F254 on a thickness of 0.25 mm.
5.2. General Pd/Cu coupling reaction procedures10
To an oven dried glass screw capped tube were added all
solids including the aryl halide .bromide or iodide), alkyne,
copper iodide, triphenylphosphine and palladium catalyst.
The atmosphere was removed via vacuum and replaced with
dry nitrogen .3£). THF, remaining liquids, and HuÈnig's
base or triethylamine were added and the reaction was
heated in an oil bath while stirring. Upon cooling the
reaction mixture was ®ltered via gravity ®ltration to remove
solids and diluted with CH2Cl2. The reaction mixture was
Scheme 11.
Scheme 12.
Nanoparticle linker 43 was synthesized according to
Scheme 12. Starting from dinitro 4112 and coupling aniline
35 afforded dinitrodianiline 42, which was subsequently
diazotized to produce 43 in good yield.
extracted with an aqueous solution of ammonium chloride
.NH4Cl) .3£). The organic layer was dried with magnesium
sulfate and ®ltered. The solvent was then removed in vacuo.
5.3. General procedure for the deprotection of
trimethylsilyl-protected alkynes
4. Conclusions
To a round bottom ¯ask equipped with a stir bar were added
the protected alkyne, potassium carbonate .5 equiv. per
protected alkyne), methanol, and methylene chloride. The
reaction was heated, and upon completion the reaction
mixture was diluted with methylene chloride and washed
with brine .3£). The organic layer was dried over MgSO4,
and the solvent removed in vacuo.
Many oligo.phenylene ethynylene)s containing reversibly
reducible functionalities based on quinone and nitro cores
have been synthesized. These molecules have methods of
attachment to a metal surface ranging from the standard
protected thiol groups to the novel diazonium and pyridyl
linkages. Work is currently underway to examine the
assembly of these various compounds on metal surfaces as
well as their ef®ciency as switches and memory devices.
5.4. General HOF oxidation procedure12
5. Experimental
To a 125 mL polyethylene bottle were added H2O .2 mL)
and CH3CN .60 mL) and cooled to 2208C. F2 .20% in He)
was then bubbled through the solution at a rate of 50 sccm
for 2 h. The resulting HOF/CH3CN solution was purged
with He for 15 min. The species to be oxidized was
added in acetone or ethyl acetate .10 mL) and mixed at
2208C for 5 min before being neutralized by pouring into
a saturated NaHCO3 solution. The organic phase was then
separated, dried over MgSO4 and the solvents were removed
in vacuo.
5.1. General procedure
All reactions were carried out under a dry nitrogen
atmosphere unless noted. Reagent grade diethyl ether and
tetrahydrofuran .THF) were distilled under nitrogen from
sodium benzophenone ketyl. Reagent grade dichloro-
methane .CH2Cl2) was distilled from calcium hydride
.CaH2) under nitrogen. Triethylamine and N,N-diisopropyl-
ethylamine .HuÈnig's base) were distilled over CaH2 under a

S. M. Dirk et al. / Tetrahedron 57 22001) 5109±5121
5115
5.5. General procedure for the diazotization of anilines
with nitrosonium tetra¯uoroborate in the acetonitrile±
sulfolane system7
reaction was heated at 608C for 2 d. The reaction was worked
up by diluting with ether, washing with aqueous ammonium
chloride .2£), drying over MgSO4, and removing the solvents
in vacuo. The crude product was puri®ed via ¯ash chromato-
graphy .CH2Cl2) to yield 430 mg .64%) of a white solid. IR
.KBr) 3373.6, 3322.4, 3086.5, 1774.0, 1681.7, 1568.9,
1528.8, 1445.8, 1389.4, 1358.6, 1245.8, 1179.1, 1112.5,
NOBF4 was weighed out in a nitrogen ®lled dry box and
placed in a round bottom ¯ask equipped with a magnetic
stirring bar and sealed with a septum. Acetonitrile and
sulfolane were injected in a 5:1 volume ratio and the
resulting suspension was cooled in a dry ice/acetone bath
to 2408C. The solution of the aniline was prepared by
adding warm sulfolane .45±508C) to the amine under a
nitrogen blanket, sonication for 1 min and subsequent
addition of acetonitrile .10±20% by volume). The aniline
solution was then added to the nitrosonium salt suspension
over a period of 10 min. The reaction mixture was kept at
2408C for 30 min and was then allowed to warm to the
room temperature. At this point, the diazonium salt was
precipitated by the addition of ether or dichloromethane,
collected by ®ltration, washed with ether or dichloro-
methane and dried. Additional puri®cation of the salt was
accomplished by re-precipitation from DMSO by dichloro-
methane and/or ether.
1
1056.1, 1030.4, 999.6, 872.0, 850.9, 768.9, 697.1 cm21. H
NMR .400 MHz, CDCl3) d 8.54 .s, 1H), 8.15 .s, 1H), 7.80 .br
s, 1H), 7.40±7.38 .m, 3H), 7.29±7.27 .m, 2H) 2.26 .s, 3H).
13C NMR .100 MHz, CDCl3) d 168.44, 143.77, 139.34,
137.74, 136.81, 128.67, 128.51, 128.47, 127.85, 123.31,
110.59, 25.05. HRMS calcd for C14H11BrN2O3: 333.9953;
found: 333.9952.
5.5.4. 2-Bromo-4-nitro-5-phenylaniline 38). 7 .500 mg,
1.49 mmol), potassium carbonate .1.031 g, 7.46 mmol),
methanol .30 mL), and methylene chloride .30 mL) were
added to a 100 mL round bottom ¯ask and stirred at room
temperature under a nitrogen blanket for 2 h. The reaction
was worked up by ®ltering off the K2CO3 and washing with
CH2Cl2 to yield 437 mg .100%) of the title compound. IR
.KBr) 3463.7, 3349.2, 3221.3, 1623.9, 1584.6, 1555.4,
1495.5, 1443.6, 1406.9, 1305.6, 1259.4, 1123.9, 1051.7,
5.5.1. 4-Ethynlphenyl-2,4-dinitrobromobenzene 35).12
2-Bromo-4-nitro-5-ethynlphenylaniline .490 mg, 1.48 mmol)
in ethyl acetate .10 mL) was oxidized according to the general
HOF oxidation procedure to yield 320 mg .60%) of a yellow
solid. IR .KBr) 3442.7, 3101.4, 2216.8, 1610.6, 1540.9,
1461.3, 1384.8, 1358.7, 1337.1, 1264.4, 906.2, 849.6, 824.4,
1
896.7, 846.5, 760.1, 701.3, 632.1, 563.8 cm21. H NMR
.400 MHz, CDCl3) d 8.21 .s, 1H), 7.39±7.36 .m, 3H),
7.23±7.21 .m .overlapping), 2H), 6.61 .s, 1H). 13C NMR
.100 MHz, CDCl3) d 148.5, 139.4, 138.5, 130.7, 128.8,
128.4, 128.2, 128.1, 117.2, 106.3. HRMS calcd: 291.9848;
found: 291.9846.
1
760.2, 689.8 cm21. H NMR .400 MHz, CDCl3) d 8.41 .s,
1H), 8.09 .s, 1H), 7.60±7.58 .m, 2H), 7.41±7.39 .m, 3H).
13C NMR .100 MHz, CDCl3) d 152.1, 150.4, 132.7, 131.7,
131.0, 130.7, 129.1, 121.5, 119.8, 113.9, 102.0. HRMS calcd:
345.9589; found: 345.9585.
5.5.5. 2,5-Dinitro-4-phenylbromobenzene 39).12 8 .373 mg,
1.28 mmol) in ethyl acetate .10 mL) was oxidized according
to the general HOF oxidation procedure to yield 407 mg
.99%) of an orange solid. IR .KBr) 3446.7, 3090.4, 1542.8,
1461.1, 1443.1, 1347.3, 1257.7, 1114.6, 1076.2, 1051.8,
1021.0, 904.5, 842.5, 768.8, 743.7, 699.9, 551.0,
5.5.2. 20,50-Dinitro-4,40-diethynylphenyl-1-thioacetyl-
benzene 31). 4 .300 mg, 0.86 mmol), 4-ethynyl.thioacetyl)-
benzene .183 mg, 1.04 mmol), bis.dibenzylideneacetone)-
palladium .12 mg, 0.02 mmol), copper.I) iodide .4 mg,
0.02 mmol), triphenylphosphine .13 mg, 0.05 mmol),
Hunig's base .0.60 mL) and THF .20 mL) were reacted
according to the general coupling procedure. The reaction
mixture was heated at 608C overnight and worked up
according to the procedure above. The crude compound
was puri®ed via ¯ash chromatography .silica, 3:1 dichloro-
methane/hexane) to yield 90 mg .24%) of a bright yellow
solid. IR .KBr) 2220.2, 1705.2, 1545.5, 1499.81, 1396.8,
1337.5, 1286.1, 1252.1, 1108.6, 1087.2, 953.2, 926.0,
1
485.16 cm21. H NMR .400 MHz, CDCl3) d 8.16 .s, 1H),
7.89 .s, 1H), 7.47±7.45 .m, 3H), 7.31±7.29 .m, 2H). 13C
NMR .100 MHz, CDCl3) d 151.5, 150.6, 137.2, 134.4,
130.8, 130.1, 129.7, 128.9, 128.1, 114.1. HRMS calcd:
321.9589; found: 321.9592.
5.5.6. 20,40-Dinitro-50-phenyl-4-ethynylphenyl-1-thioacetyl-
benzene 32). 9 .147 mg, 0.46 mmol), 4-ethynyl.thioacetyl)-
benzene .106 mg, 0.60 mmol), bis.dibenzylideneacetone)-
palladium .26 mg, 0.05 mmol), copper.I) iodide .9 mg,
0.05 mmol), triphenylphosphine .12 mg, 0.05 mmol), HuÈnig's
base .0.16 mL) and THF .20 mL) were coupled according to
the general coupling procedure. The reaction mixture was
stirred and heated overnight at 458C. Crude product was
puri®ed via column chromatography .silica, 3:1 dichloro-
methane/hexanes) to yield 75 mg of an orange solid .39%).
IR .KBr) 2922.7, 2214.3, 1702.7, 1542.8, 1488.1, 1357.1,
1271.1, 1115.1, 1088.6, 956.0, 908.6, 829.9, 770.5, 707.0,
.
868.3, 827.2, 756.7, 684.1, 618.3 cm21 1H NMR
.400 MHz, CDCl3) d 8.34 .d, Jˆ0.4 Hz, 1H), 8.35 .d,
Jˆ0.4 Hz, 1H), 7.63±7.59 .m, 4H), 7.46±7.40 .m, 5H),
2.49 .s, 3H). 13C NMR .100 MHz, CDCl3) d 193.2, 151.1,
134.7, 133.1, 132.7, 131.0, 130.7, 129.1, 122.8, 121.7,
119.4, 118.6, 102.4, 100.9, 84.8, 83.5, 30.8. HRMS calcd:
442.0623; found: 442.0634.
1
623.4 cm21. H NMR .400 MHz, CDCl3) d 8.16 .s, 1H),
8.10 .s, 1H), 7.63 .d, Jˆ8.4 Hz, 2H), 7.48±7.44 .m, 5H),
7.36±7.33 .m, 2H), 2.44 .s, 3H). 13C NMR .100 MHz,
CDCl3) d 193.3, 151.2, 150.6, 136.8, 134.8, 134.7, 133.1,
130.8, 130.2, 130.1, 129.6, 128.6, 128.1, 122.9, 119.0, 99.8,
84.5, 30.8. HRMS calcd: 418.0623; found: 418.0619.
5.5.3. 2-Bromo-4-nitro-5-phenylacetanilide 37). 6 .676 mg,
2 mmol), triphenylphosphine .52 mg, 0.2 mmol), phenyl-
boronic acid .293 mg, 2.4 mmol), bis.triphenylphosphine)-
palladium dichloride .70 mg, 0.1 mmol), and cesium
carbonate .977 mg, 3 mmol) were placed in a 100 mL
round bottom ¯ask and the atmosphere was removed and
replaced with nitrogen. Toluene .30 mL) was added and the
5.5.7. 2,5-Dibromo-1,4-dimethoxybenzene16 311). In a

5116
S. M. Dirk et al. / Tetrahedron 57 22001) 5109±5121
100 mL round bottom ¯ask, 1,4-dimethoxybenzene .10.0 g,
72.4 mmol) was dissolved in glacial acetic acid .20 mL). A
solution of bromine .7.42 mL, 145.0 mmol) in glacial acetic
acid .7.5 mL) was added dropwise to the ®rst solution at
room temperature over 40 min. The resulting mixture was
allowed to stir for 2 h. The crude product was washed with
ice-cold water and ice-cold methanol to afford ®ne white
crystals. The mother liquor was concentrated and cooled to
afford more white crystals .15.9 g, 74% yield). Mp 136±
1388C .lit21 mp 144±1458C). IR .KBr) 3091.9, 3022.1,
2968.8, 2944.4, 2842.8, 1694.9, 1494.2, 1475.6, 1436.5,
1358.2, 1275.0, 1211.8, 1185.0, 1065.4, 1021.9, 860.5,
acetone)palladium .0.036 g, 0.063 mmol), copper.I) iodide
.0.012 g, 0.063 mmol), triphenylphosphine .0.042 g,
0.16 mmol), THF .20 mL), HuÈnig's base .2.2 mL,
12.6 mmol), and trimethylsilylacetylene .0.89 mL,
6.3 mmol) were used following the general procedure for
couplings. The tube was capped and heated in a 608C oil
bath for 1 d. Flash column chromatography .silica gel using
24:1 hexanes/ethyl acetate as eluent) afforded the desired
product slightly impure .0.83 g, 79% yield). 1H NMR
.400 MHz, CDCl3) d 7.55 .m, 2H), 7.32 .m, 3H), 6.98 .s,
1H), 6.95 .s, 1H), 3.84 .s, 3H), 3.83 .s, 3H), 0.27 .s, 9H).
1
760.4, 441.8 cm21. H NMR .400 MHz, CDCl3) d 7.13 .s,
5.5.12. 1,4-Dimethoxy-2-ethynyl-5-3ethynylphenyl)benzene
315).
2H), 3.87 .s, 6H). 13C NMR .100 MHz, CDCl3) d 150.93,
117.53, 110.90, 57.43.
1,4-Dimethoxy-2-ethynylphenyl-5-.trimethylsilyl-
ethynyl)benzene .0.830 g, 2.48 mmol), potassium carbonate
.1.71 g, 12.4 mmol), methanol .50 mL), and dichloro-
methane .50 mL) were used following the general
procedure for deprotection to afford the desired product
5.5.8. 2,5-Di3ethynylphenyl)-1,4-dimethoxybenzene 312).
11 .8.745 g, 29.55 mmol), bis.triphenylphosphine)palladium
dichloride .0.415 g, 0.591 mmol), copper.I) iodide .0.225 g,
1.182 mmol), triphenylphosphine .0.310 g, 1.182 mmol),
THF .35 mL), HuÈnig's base .20.5 mL, 118 mmol), and
phenylacetylene .7.8 mL, 70.92 mmol) were used following
the general procedure for couplings. The solution was
heated in a 658C oil bath for 3 d. Recrystallization from
benzene afforded the desired product, mp 175±1778C
.lit.16 176±1778C) .9.22 g, 92%). 1H NMR .400 MHz,
CDCl3) d 7.57 .m, 4H), 7.34 .m, 6H), 7.03 .s, 2H), 3.89
.s, 6H). 13C NMR .100 MHz, CDCl3) d 154.10, 131.89,
128.60, 128.50, 123.39, 115.86, 113.57, 95.23, 85.86, 56.66.
1
.0.513 g, 79% yield). H NMR .400 MHz, CDCl3) d 7.55
.m, 2H), 7.33 .m, 3H), 7.00 .s, 1H), 6.98 .s, 1H), 3.87 .s,
3H), 3.86 .s, 3H), 3.39 .s, 1H).
5.5.13. 4,40-Di3ethynylphenyl)-20,50-dimethoxy-1-benzene-
thioacetate 316). 15 .0.513 g, 1.96 mmol), bis.dibenzylid-
eneacetone)palladium.0) .0.058 g, 0.10 mmol), copper.I)
iodide .0.019 g, 0.10 mmol), triphenylphosphine .0.066 g,
0.25 mmol), THF .20 mL), HuÈnig's base .1.37 mL,
7.84 mmol), and 4-.thioacetyl)iodobenzene .0.608 g,
2.16 mmol) were used following the general procedure for
couplings. The tube was capped and heated in a 558C oil
bath for 3 d. Flash column chromatography .silica gel using
dichloromethane as eluent) afforded the desired product
5.5.9. 2,5-Di3ethynylphenyl)benzoquinone 313). 12 .0.300 g,
0.886 mmol) and THF .6 mL) were added to a 25 mL round
bottom ¯ask containing a stir bar. A solution of ceric ammo-
nium nitrate .1.46 g, 2.658 mmol) in water .3 mL) was slowly
added to the ¯ask and allowed to stir for 15 min. Water was
added and the organic materials were extracted with dichloro-
methane. Flash column chromatography .silica gel using 1:1
hexanes/dichloromethane as eluent) afforded the desired
product .0.129 g, 47%). IR .KBr) 3047.5, 2203.0, 1716.2,
1655.3, 1568.3, 1215.4, 1100.6, 902.1, 757.6, 686.4 cm21.
1H NMR .400 MHz, CDCl3) d 7.58 .dd, Jˆ7.9, 1.5 Hz,
4H), 7.38 .m, 6H), 6.99 .s, 2H). 13C NMR .100 MHz,
CDCl3) d 182.87, 136.55, 133.34, 132.83, 130.57,128.97,
121.83, 105.26, 82.90. HRMS calcd for C22H12O2:
308.0837; found: 308.0834.
1
slightly impure .0.621 g, 76% yield). H NMR .400 MHz,
CDCl3) d 7.57 .m, 4H), 7.38 .d, Jˆ8.1 Hz, 2H), 7.33 .m,
3H), 7.03 .s, 1H), 7.02 .s, 1H), 3.874 .s, 3H), 3.870 .s, 3H),
2.40 .s, 3H).
5.5.14. 2-Ethynylphenyl-5-3340-thioacetyl)ethynylphenyl)-
benzoquinone 317). 16 .0.050 g, 0.12 mmol), acetonitrile
.5 mL), and THF .5 mL) were added to a 25 mL round
bottom ¯ask containing a stir bar. A solution of ceric
ammonium nitrate .0.13 g, 0.24 mmol) in water .1 mL)
was added in one portion. After stirring at room temperature
for 30 min, another equivalent solution of ceric ammonium
nitrate .0.13 g, 0.24 mmol) was added. After 20 additional
minutes, the reaction was quenched by adding water
.30 mL) to effect precipitation of an orange solid. Flash
column chromatography .silica gel using dichloromethane
as eluent) afforded the desired product .0.034 g, 74% yield).
IR .KBr) 3053.0, 2924.3, 2852.6, 2205.4, 1703.4, 1652.7,
1568.8, 1483.7, 1442.2, 1354.8, 1221.3, 1105.4, 1089.4,
5.5.10. 2-Bromo-5-ethynylphenyl-1,4-dimethoxybenzene
314). 11 .2.96 g, 10.0 mmol), bis.dibenzylideneacetone)-
palladium .0.115 g, 0.20 mmol), copper.I) iodide .0.038 g,
0.20 mmol), triphenylphosphine .0.131 g, 0.50 mmol), THF
.15 mL), HuÈnig's base .6.97 mL, 40.0 mmol) and phenyl-
acetylene .1.21 mL, 11.0 mmol) were used following the
general procedure for coupling. The tube was heated in a
508C oil bath for 18 h. Column chromatography .silica gel
using 19:1 hexanes/diethyl ether as eluent) afforded the
desired product, somewhat impure .approximately 15%
impurities by NMR) in moderate yield .1.02 g, 32%
yield). This was taken onto the next step in this impure
1
949.6, 920.1, 830.9, 758.2, 688.2, 620.6 cm21. H NMR
.400 MHz, CDCl3) d 7.58 .m, 4H), 7.42 .m, 2H), 7.38 .m,
3H), 6.98 .s, 1H), 6.97 .s, 1H), 2.42 .s, 3H). 13C NMR
.100 MHz, CDCl3) d 193.22, 182.74, 182.67, 136.88,
136.51, 134.63, 133.34, 133.24, 132.99, 132.84, 130.94,
130.63, 128.99, 122.81, 121.80, 105.38, 103.99, 84.17,
82.92, 30.80. HRMS calcd for C24H14O3S: 382.0664;
found: 382.0663.
1
form. H NMR .400 MHz, CDCl3) d 7.54 .m, 2H), 7.33
.m, 3H), 7.09 .s, 1H), 7.02 .s, 1H), 3.86 .s, 6H).
5.5.15. 1,4-Dimethoxy-2,5-bis3trimethylsilylethynyl)-
benzene. 11 .1.75 g, 5.91 mmol), bis.triphenylphosphine)-
palladium dichloride .0.207 g, 0.296 mmol), copper.I)
5.5.11. 1,4-Dimethoxy-2-ethynylphenyl-5-3trimethylsilyl-
ethynyl)benzene. 14 .1.0 g, 3.15 mmol), bis.dibenzylidene-

S. M. Dirk et al. / Tetrahedron 57 22001) 5109±5121
5117
iodide .0.113 g, 0.591 mmol), triphenylphosphine .0.155 g,
0.591 mmol), THF .20 mL), HuÈnig's base .4.1 mL,
23.64 mmol), and trimethylsilylacetylene .2.51 mL, 17.73
mmol) were used following the general procedure for
couplings. The tube was capped and heated in a 558C oil
bath for 2 d. Flash column chromatography .silica gel using
1:1 hexanes/dichloromethane as eluent) afforded the desired
product .1.54 g, 79% yield). IR .KBr) 2957.0, 2898.2,
2851.2, 2829.0, 2149.1, 1496.8, 1464.1, 1449.1, 1388.2,
1283.7, 1249.0, 1223.6, 1203.1, 1172.4, 1039.6, 883.2,
To a solution of 2,5-dibromonitrobenzene .0.28 g, 0.997
mmol), bis.triphenylphosphine)palladium dichloride .0.07 g,
0.098 mmol), copper.I) iodide .0.019 g, 0.098 mmol),
triphenylphosphine .0.106 g, 0.40 mmol) and K2CO3
.1.1 g, 7.96 mmol) in THF .4 mL) were added via a cannula
21 .0.377 g, 2.15 mmol) in THF .4 mL) and MeOH .2 mL).
The mixture was heated at 648C for 20 h. The solvent was
removed by rotary evaporation and the black residue was
washed with aqueous K2CO3 and extracted with Et2O. The
combined organic layers were dried over Na2SO4, ®ltered,
and the solvent evaporated in vacuo. Puri®cation by ¯ash
chromatography .silica gel, hexane/AcOEt 70:30, 50:50,
20:80, 0:100) afforded 60 mg .24% yield) of the title
compound as a yellow solid. Mp 178±1808C. IR .KBr)
3414.0, 3036.7, 1616.0, 1589.4, 1538.1, 1519.9, 1407.9,
841.3, 757.4, 714.9, 696.2, 626.4 cm21
.
1H NMR
.400 MHz, CDCl3) d 6.89 .s, 2H), 3.81 .s, 6H), 0.25 .s,
18H). 13C NMR .100 MHz, CDCl3) d 154.56, 116.59,
113.81, 101.22, 100.84, 56.83, 0.40. HRMS calcd for
C18H26O2Si2: 330.1471; found: 330.1468.
1
1345.7, 1271.1, 1214.1, 828.3 cm21. H NMR .400 MHz,
5.5.16. 1,4-Dimethoxy-2,5-diethynylbenzene 318). 1,4-
Dimethoxy-2,5-bis.trimethylsilylethynyl)benzene .1.50 g,
4.54 mmol), potassium carbonate .6.27 g, 45.4 mmol),
methanol .50 mL), and dichloromethane .50 mL) were
used following the general procedure for deprotection to
give the desired product .0.829 g, 98%). 1H NMR
.400 MHz, CDCl3) d 6.96 .s, 2H), 3.84 .s, 6H), 3.37 .s, 2H).
DMSO-d) d 8.69 .br s, 4H), 8.44 .d, Jˆ1.4 Hz, 1H), 8.04
.1/2 ABqd, Jˆ8.0, 1.4 Hz, 1H), 7.99 .1/2 ABq, Jˆ8.0 Hz,
1H), 7.60 .d, Jˆ5.8 Hz, 2H), 7.57 .d, Jˆ5.8 Hz, 2H). 13C
NMR .100 MHz, DMSO-d) d 150.21, 150.13, 149.42,
136.27, 135.36, 129.16, 129.11, 127.96, 125.50, 125.39,
123.25, 116.55, 94.98, 90.63, 90.59, 88.13. HRMS calcd
for C20H11N3O2: 325.0851; found: 325.0847.
5.5.17. 2,5-Bis340-3thioacetyl)ethynylphenyl)-1,4-dimethoxy-
benzene 319). 18 .0.810 g, 4.35 mmol), bis.dibenzylidene-
acetone)palladium .0.253 g, 0.44 mmol), copper.I) iodide
.0.084 g, 0.44 mmol), triphenylphosphine .0.115 g, 0.44
mmol), THF .30 mL), HuÈnig's base .4.5 mL, 26.1 mmol),
and 4-.thioacetyl)iodobenzene22 .2.54 g, 9.14 mmol) were
used following the general procedure for couplings. The
solution was stirred in a 608C oil bath for 16 h. Crystalliza-
tion from dichloromethane/hexanes afforded the desired
product .1.81 g, 85%). IR .KBr) 3129.1, 3057.4, 3006.2,
2975.5, 2940.0, 2847.4, 2207.2, 1697.7, 1506.8, 1483.1,
1463.1, 1396.2, 1279.2, 1223.5, 1122.2, 1034.2, 949.5,
5.5.20. 1-Bromo-4-340-ethynylpyridyl)-3-nitrobenzene
323). To a solution of 2,5-dibromonitrobenzene .0.43 g,
1.53 mmol), bis.triphenylphosphine)palladium.II) dichloride
.0.052 g, 0.074 mmol), copper.I) iodide .0.015 g, 0.078
mmol), triphenylphosphine .0.079 g, 0.30 mmol) and
K2CO3 .0.83 g, 6.0 mmol) in THF .2 mL) were added via
a cannula 21 .0.342 g, 1.95 mmol) in THF .4 mL) and
MeOH .1.5 mL). The mixture was heated at 238C for 2 d.
The solvent was removed by rotary evaporation and the
residue was diluted with water and extracted with Et2O.
The combined organic layers were dried over Na2SO4,
®ltered, and the solvent evaporated in vacuo. Puri®cation
by ¯ash chromatography .silica gel, hexane/AcOEt 90:10,
70:30, 50:50) afforded 330 mg .71% yield) of the title
compound as an off-white solid. Mp 166±1718C. IR .KBr)
3424.4, 3093.3, 1592.3, 1521.4, 1409.3, 1341.4,
898.8, 825.5, 765.6, 616.8 cm21 1H NMR .400 MHz,
.
CDCl3) d 7.57 .dt, Jˆ8.5, 1.9 Hz, 4H), 7.39 .dt, Jˆ8.5,
2.0 Hz, 4H), 7.01 .s, 2H), 3.89 .s, 6H), 2.42 .s, 6H). 13C
NMR .100 MHz, CDCl3) d 193.85, 154.43, 134.58, 132.65,
128.64, 124.84, 116.08, 113.75, 94.76, 87.73, 56.91, 30.70.
HRMS calcd for C28H22O4S2: 486.0960; found: 486.0956.
1
1272.6 cm21. H NMR .400 MHz, CDCl3) d 8.68 .br s,
2H), 8.29 .d, Jˆ1.9 Hz, 1H), 7.79 .dd, Jˆ8.3, 2.0 Hz,
1H), 7.62 .d, Jˆ8.3 Hz, 1H), 7.44 .d, Jˆ4.7 Hz, 2H). 13C
NMR .100 MHz, CDCl3) d 149.96, 136.22, 135.69, 130.14,
128.08, 126.67, 125.65, 123.19, 116.48, 94.80, 87.81.
HRMS calcd for C13H7BrN2O2: 303.9672; found: 303.9682.
5.5.18. 2,5-Bis340-3thioacetyl)ethynylphenyl)benzoquinone
320). 19 .0.050 g, 0.103 mmol), acetonitrile .5 mL), and
THF .3 mL) were added to a 25 mL round bottom ¯ask
containing a stir bar. A solution of ceric ammonium nitrate
.0.339 g, 0.618 mmol) in water .2 mL) was added in two
portions at 30 min intervals. After stirring at room tempera-
ture for 3 h, the reaction was quenched by adding water to
effect precipitation of an orange solid. Flash column
chromatography .silica gel using dichloromethane as
eluent) afforded the desired product .0.023 g, 49% yield).
IR .KBr) 2922.2, 2847.4, 2203.4, 1694.9, 1660.1, 1569.9,
1351.8, 1212.3, 1119.7, 1084.6, 1013.2, 960.3, 826.8,
5.5.21. 5-Ethynylphenyl-2-340-ethynylpyridyl)-1-nitro-
benzene 324). To a solution of 23 .88.8 mg, 0.293 mmol),
bis.triphenylphosphine)palladium.II) dichloride .0.011 g,
0.016 mmol), copper.I) iodide .0.004 g, 0.021 mmol)
and triphenylphosphine .0.008 g, 0.029 mmol) in
THF .4 mL) were added Et3N .0.25 mL, 1.76 mmol) and
phenylacetylene .0.1 mL, 9.1 mmol). The mixture was
stirred at 568C for 36 h. The solvent was evaporated in
vacuo. The residue was diluted with water and extracted
with Et2O. The combined organic layers were dried over
MgSO4, ®ltered, and the solvent evaporated in vacuo. Puri-
®cation by ¯ash chromatography .silica gel, AcOEt/hexane
20:80) afforded 65 mg .69% yield) of the title compound as
a yellow solid. Mp 130±1328C. IR .KBr) 3445.3, 3046.3,
620.6 cm21 1H NMR .400 MHz, CDCl3) d 7.60 .dt,
.
Jˆ8.3, 1.6 Hz, 4H), 7.42 .dt, Jˆ8.3, 1.6 Hz, 4H), 7.00 .s,
2H), 2.43 .s, 6H). 13C NMR .100 MHz, CDCl3) d 193.23,
182.61, 136.86, 134.64, 133.25, 133.07, 130.97, 122.78,
104.14, 84.08, 30.79. HRMS calcd for C26H16O4S2:
456.0500; found: 456.0490.
2203.5, 1548.5, 1529.1, 1399.9, 1341.6 cm21
.
1H NMR
5.5.19. 2,5-Bis340-ethynylpyridyl)-1-nitrobenzene 322).
.400 MHz, CDCl3) d 8.67 .br d, Jˆ4.9 Hz, 2H), 8.27 .d,

5118
S. M. Dirk et al. / Tetrahedron 57 22001) 5109±5121
Jˆ1.5 Hz, 1H), 7.76 .1/2 ABqd, Jˆ8.0, 1.6 Hz, 1H), 7.72
.1/2 ABqd, Jˆ8.0, 0.5 Hz, 1H), 7.56 .m, 2H), 7.45 .dd,
Jˆ5.9, 1.7 Hz, 2H), 7.40 .m, 3H). 13C NMR .100 MHz,
CDCl3) d 149.58, 135.39, 134.65, 131.81, 129.34, 128.54,
127.67, 125.32, 121.85, 116.66, 95.30, 94.30, 88.52, 86.63.
HRMS calcd for C21H12N2O2: 324.0899; found: 324.0895.
chromatography .silica gel, CH2Cl2/hexane 35:65) afforded
410 mg .47% yield) of the title compound as an off-white
solid. Mp 162±1648C. IR .KBr) 3372.9, 2962.9, 2146.0,
1727.2, 1611.2, 1544.9, 1501.5, 1457.1, 1404.3, 1338.2,
1
1250.6, 1222.3, 881.9 cm21. H NMR .400 MHz, CDCl3)
d 8.75 .s, 1H), 8.15 .s, 1H), 8.10 .br s, 1H), 2.27 .s, 3H),
0.33 .s, 9H), 0.28 .s, 9H). 13C NMR .100 MHz, CDCl3) d
168.21, 144.19, 142.41, 128.11, 123.82, 120.18, 111.52,
106.66, 106.16, 99.50, 97.44, 24.90, 20.31, 20.46.
HRMS calcd for C18H24N2O3Si2: 372.1326; found:
372.1326.
5.5.22. 1-Bromo-4-ethynylphenyl-3-nitrobenzene 325).
To a solution of 2,5-dibromonitrobenzene .0.937 g, 3.34
mmol), bis.dibenzylideneacetone)palladium .0.095 g,
0.166 mmol), copper.I) iodide .0.032 g, 0.168 mmol) and
triphenylphosphine .0.173 g, 0.66 mmol) in THF .4 mL)
were added Et3N .1 mL, 7.2 mmol) and phenylacetylene
.0.5 mL, 4.56 mmol). The mixture was stirred at 238C for
48 h. The mixture was washed with a saturated solution of
NH4Cl and then extracted with Et2O. The combined organic
layers were dried over Na2SO4, ®ltered, and the solvent
evaporated in vacuo. Puri®cation by ¯ash chromatography
.silica gel, CH2Cl2/hexane 1:8) afforded 0.48 g .47% yield)
of the title compound as a yellow solid. Mp 58±748C. IR
.KBr) 3421.9, 3085.5, 2213.4, 1595.7, 1545.9, 1521.3,
5.5.25. 2,5-Bis340-ethynylpyridyl)-4-nitroaniline 328). To
a solution of 27 .0.056 g, 0.15 mmol), 4-iodopyridine
.0.08 g, 0.39 mmol), K2CO3 .0.17 g, 1.2 mmol), bis.tri-
phenylphosphine)palladium.II) dichloride .0.01 g, 0.015
mmol), copper.I) iodide .0.004 g, 0.021 mmol) and tri-
phenylphosphine .0.016 g, 0.061 mmol) in THF .4 mL)
was added MeOH .1 mL). The mixture was heated at
608C for 50 h. The solvent was removed by rotary evapora-
tion and the brown residue was diluted with water and
extracted with AcOEt. The combined organic phases were
dried over Na2SO4, ®ltered, and the solvent evaporated in
vacuo. Puri®cation by ¯ash chromatography .silica gel,
AcOEt) afforded 8 mg .16% yield) of the title compound
as a yellow solid. Mp 154±1608C. IR .KBr) 3730.2, 3438.6,
2204.8, 1592.4, 1541.1, 1409.8, 1308.5, 1249.9,
1
1336.5, 1269.2 cm21. H NMR .400 MHz, CDCl3) d 8.23
.d, Jˆ1.9 Hz, 1H), 7.72 .dd, Jˆ8.3 Hz, 2.0, 1H), 7.59 .m,
3H), 7.40 .m, 3H). 13C NMR .100 MHz, CDCl3) d 149.71,
135.91, 135.45, 131.99, 129.44, 128.46, 127.78, 122.03,
121.75, 117.69, 98.43, 84.00. HRMS calcd for
C14H8NO2Br: 302.9720; found: 302.9725.
818.8 cm21 1H NMR .400 MHz, CDCl3) d 8.67 .dd,
.
5.5.23. 2-Ethynylphenyl-5-340-ethynylpyridyl)-1-nitro-
benzene 326). To a solution of 25 .0.306 g, 1.01 mmol),
K2CO3 .0.713 g, 5.16 mmol), bis.triphenylphosphine)-
palladium dichloride .0.035 g, 0.05 mmol), copper.I) iodide
.0.009 g, 0.047 mmol) and triphenylphosphine .0.052 g,
0.198 mmol) in THF .2 mL) were added via a cannula 21
.0.217 g, 1.24 mmol) in THF .2 mL) and MeOH .1 mL).
The mixture was heated at 608C for 18 h. The solvent was
removed by rotary evaporation and the brown residue was
diluted with water and extracted with Et2O. The combined
organic layers were dried over Na2SO4, ®ltered, and the
solvent evaporated in vacuo. Puri®cation by ¯ash chromato-
graphy .silica gel, AcOEt/hexane 20:80, 40:60) afforded
260 mg .79% yield) of the title compound as a yellow
solid. Mp 144±1468C. IR .KBr) 3442.3, 3053.0, 2209.4,
1631.3, 1584.8, 1524.7, 1404.3, 1344.7, 1269.0, 826.4,
Jˆ4.4, 1.7 Hz, 2H), 8.65 .dd, Jˆ4.5, 1.7 Hz, 2H), 8.34 .s,
1H), 7.44 .dd, Jˆ4.5, 1.7 Hz, 2H), 7.40 .dd, Jˆ4.4, 1.6 Hz,
2H), 6.99 .s, 1H), 5.03 .br s, 2H). 13C NMR .100 MHz,
CDCl3) d 151.26, 150.03, 149.90, 139.56, 130.71, 130.52,
130.00, 125.65, 125.33, 120.33, 118.52, 106.57, 94.67,
94.19, 89.55, 87.27. HRMS calcd for C20H12N4O2:
340.0960; found: 340.0958.
5.5.26.
2-Amino-4-340-ethynylpyridyl)-5-nitrobromo-
benzene 329). To a solution of 6 .0.877 g, 8.84 mmol),
K2CO3 .1.08 g, 7.81 mmol), bis.triphenylphosphine)palla-
dium dichloride .0.054 g, 0.077 mmol), copper.I) iodide
.0.025 g, 0.13 mmol) and triphenylphosphine .0.068 g,
0.26 mmol) in THF .4 mL) were added via a cannula 21
.0.404 g, 2.30 mmol) in THF .8 mL) and MeOH .3 mL).
The mixture was stirred at 238C for 1 d. The solvent was
evaporated in vacuo. The residue was diluted with water and
extracted with AcOEt. The combined organic phases were
dried over MgSO4, ®ltered and the solvent evaporated in
vacuo. Puri®cation by ¯ash chromatography .silica gel,
AcOEt/hexane 40:60, 50:50) afforded 290 mg .39% yield)
of the title compound as a yellow solid. Mp 226±2288C. IR
.KBr) 3385.4, 3297.7, 3171.3, 1646.8, 1591.7, 1556.9,
1
755.2, 686.6 cm21. H NMR .400 MHz, CDCl3) d 8.67
.dd, Jˆ4.4, 1.6 Hz, 2H), 8.27 .br s, 1H), 7.74 .m, 2H),
7.63 .d, Jˆ1.8 Hz, 1H), 7.60 .m, 1H), 7.42 .m, 5H). 13C
NMR .100 MHz, CDCl3) d 149.99, 135.41, 134.65,
132.14, 130.19, 129.61, 128.54, 127.95, 125.50, 122.68,
122.06, 119.15, 99.67, 90.83, 90.27, 84.62. HRMS calcd
for C21H12N2O2: 324.0899; found: 324.0897.
1471.3, 1297.8 cm21 1H NMR .400 MHz, DMSO-d) d
.
5.5.24. 2,5-Bis3trimethylsilylethynyl)-4-nitroacetanilide
327). To a solution of 6 .0.78 g, 2.3 mmol), bis.dibenzyl-
ideneacetone)palladium .0.068 g, 0.118 mmol), copper.I)
iodide .0.023 g, 0.012 mmol), and triphenylphosphine
.0.123 g, 0.47 mmol) in THF .8 mL) were added Et3N
.1 mL, 7.2 mmol) and trimethylsilylacetylene .1 mL,
7.0 mmol). The mixture was heated at 678C for 48 h. The
solvent was removed by rotary evaporation and the brown
residue was diluted with water and extracted with Et2O. The
combined organic phases were dried over Na2SO4, ®ltered,
and the solvent evaporated in vacuo. Puri®cation by ¯ash
8.66 .br d, Jˆ3.8 Hz, 2H), 8.32 .d, Jˆ1.3 Hz, 1H), 7.53
.br d, Jˆ4.5 Hz, 2H), 7.06 .d, Jˆ1.3 Hz, 1H), 6.94 .br s,
2H). 13C NMR .100 MHz, DMSO-d) d 151.33, 150.12,
136.44, 130.70, 129.64, 125.32, 118.13, 117.73, 106.02,
91.85, 89.72. HRMS calcd for C13H8BrN3O2: 316.9800;
found: 316.9801.
5.5.27. 4-Amino-2-340-ethynylpyridyl)-1-nitro-5-3trimethyl-
silylethynyl)benzene. To a solution of 29 .0.310 g,
0.975 mmol), bis.triphenylphosphine)palladium dichloride
.0.035 g, 0.05 mmol), copper.I) iodide .0.011 g,

S. M. Dirk et al. / Tetrahedron 57 22001) 5109±5121
5119
0.05 mmol) and triphenylphosphine .0.026 g, 0.10 mmol) in
THF .10 mL) were added Et3N .0.9 mL, 6.5 mmol) and
trimethylsilylacetylene .0.2 mL, 1.4 mmol). The mixture
was stirred at 608C for 2 d. The solvent was evaporated in
vacuo. The residue was diluted with water and extracted
with AcOEt. The combined organic phases were dried
over MgSO4, ®ltered, and the solvent evaporated in vacuo.
Puri®cation by ¯ash chromatography .silica gel, Et2O)
afforded 160 mg .49% yield) of the title compound as a
yellow solid. Mp 145±1508C. IR .KBr) 3451.9, 3379.1,
2960.5, 2149.5, 1620.4, 1597.9, 1545.5, 1512.2,
5.5.30. 2-340-Ethynylpyridyl)-4-nitro-5-phenylaniline 332).
To a solution of 7 .80.5 mg, 0.241 mmol), K2CO3 .0.151 g,
1.09 mmol), bis.triphenylphosphine)palladium.II) dichloride
.0.009 g, 0.014 mmol), copper.I) iodide .0.003 g,
0.014 mmol) and triphenylphosphine .0.014 g, 0.053 mmol)
in THF .2 mL) were added via a cannula 1 .0.053 g,
0.3 mmol) in THF .2 mL) and MeOH .1 mL). The mixture
was heated to 708C for 3 d. The solvent was removed by
rotary evaporation and the brown residue was diluted with
water and extracted with Et2O. The combined organic layers
were dried over Na2SO4, ®ltered and the solvent evaporated
in vacuo. Puri®cation by ¯ash chromatography .silica gel,
AcOEt/hexane 30:70) afforded 60 mg .79% yield) of the
title compound as a yellow solid. Mp 187±1908C. IR .KBr)
3410.2, 3323.4, 3212.1, 2215.1, 1627.6, 1592.4, 1548.4,
1317.0 cm21 1H NMR .400 MHz, CDCl3) d 8.65 .dd,
.
Jˆ4.6, 1.5 Hz, 2H), 8.25 .s, 1H), 7.44 .dd, Jˆ4.3, 1.5 Hz,
2H), 6.93 .s, 1H), 4.90 .s, 2H), 0.30 .s, 9H). 13C NMR
.100 MHz, CDCl3) d 151.44, 149.90, 139.35, 130.65,
130.43, 125.65, 119.56, 118.06, 107.93, 104.28, 98.37,
93.70, 89.79, 20.15. HRMS calcd for C18H17N3O2Si:
335.1090; found: 335.1089.
1
1511.7, 1410.5, 1331.9 cm21. H NMR .400 MHz, CDCl3)
d 8.64 .br d, Jˆ4.8 Hz, 2H), 8.16 .s, 1H), 7.39 .m, 5H), 7.27
.m, 2H), 6.62 .s, 1H), 5.03 .br s, 2H). 13C NMR .100 MHz,
CDCl3) d 151.23, 149.82, 140.65, 138.82, 138.19, 130.49,
128.36, 128.06, 127.52, 125.34, 116.41, 104.85, 93.24, 87.89.
HRMS calcd for C19H13N3O2: 315.1008; found: 315.1011.
5.5.28. 4-Amino-5-ethynyl-2-340-ethynylpyridyl)-1-nitro-
benzene 330). To a solution of 4-amino-2-.40-ethynyl-
pyridyl)-1-nitro-5-.trimethylsilylethynyl)benzene .160 mg,
0.477 mmol) in MeOH .15 mL) and CH2Cl2 .15 mL) was
added K2CO3 .0.66 g, 4.77 mmol). The solution was stirred
at 238C for 2 h. The reaction mixture was diluted with water
and extracted with AcOEt. The combined organic layers
were dried over MgSO4, ®ltered, and the solvent evaporated
in vacuo. The reaction afforded 0.11 g .88% yield) of the
title compound as a yellow solid. The product was too
5.5.31. 1-Bromo-4-340-ethynyl)pyridine-3-nitrobenzene
334). To a solution of 331 .0.84 g, 2.34 mmol), bis.triphenyl-
phosphine)palladium dichloride .0.083 g, 0.117 mmol),
copper.I) iodide .0.022 g, 0.117 mmol), and K2CO3
.1.94 g, 14.04 mmol) in THF .4 mL) were added 21
.0.451 g, 2.57 mmol) in THF 12 mL) via a cannula and
MeOH .4 mL). The mixture was heated to 558C for 14 h.
The solvent was removed by rotary evaporation and the
residue was diluted with water, washed with brine and
extracted with AcOEt. The combined organic phases were
dried over MgSO4, ®ltered and the solvent evaporated in
vacuo. Puri®cation by ¯ash chromatography .silica gel,
AcOEt) afforded 271 mg .34% yield) of the title compound
as a yellow solid. Mp 224±2298C. IR .KBr) 3451.7, 3351.1,
3202.6, 2206.4, 1622.9, 1588.4, 1539.0, 1474.4, 1306.7,
1
unstable to attain its complete characterization data. H
NMR .400 MHz, DMSO-d) d 8.67 .dd, Jˆ4.5, 1.6 Hz,
2H), 8.12 .s, 1H), 7.53 .dd, Jˆ4.5, 1.6 Hz, 2H), 7.03 .s,
1H), 6.97 .br s, 2H), 4.70 .s, 1H).
5.5.29. 4-Amino-2-340-ethynylpyridyl)-5-340-thioacetyl-
phenylethynyl)-1-nitrobenzene 331). To a solution of 30
.0.110 g, 0.418 mmol), 4-thioacetyliodobenzene10 .0.124 g,
0.446 mmol), bis.triphenylphosphine)palladium.II) dichlor-
ide .0.015 g, 0.021 mmol), copper.I) iodide .0.004 g,
0.021 mmol) and triphenylphosphine .0.014 g, 0.053
mmol) in THF .13 mL) was added Et3N .0.4 mL,
2.9 mmol). The mixture was stirred at 508C for 2 d. The
reaction was checked by TLC .AcOEt/hexane 75:25).
More bis.triphenylphosphine)palladium dichloride .0.014 g,
0.020 mmol), copper.I) iodide .0.035 g, 0.018 mmol) and
triphenylphosphine .0.085 g, 0.324 mmol) were added and
the reaction was stirred at 608C for 1 d. The solvent was
evaporated in vacuo. The residue was diluted with water
and extracted with AcOEt. The combined organic layers
were dried over MgSO4, ®ltered, and the solvent evaporated
in vacuo. Puri®cation by ¯ash chromatography .silica gel,
AcOEt/hexane 66:33) afforded 130 mg .75% yield) of the
title compound as a yellow solid. Mp 185±1888C. IR .KBr)
3438.2, 3195.9, 2922.4, 1695.4, 1627.7, 1596.5, 1545.1,
1514.8, 1477.2, 1402.8, 1316.4, 1249.9 cm21. 1H NMR
.400 MHz, DMSO-d) d 8.68 .br d, Jˆ4.0 Hz, 2H), 8.23 .s,
1H), 7.79 .d, Jˆ8.1 Hz, 2H), 7.54 .d, Jˆ5.0 Hz, 2H), 7.49 .d,
Jˆ8.0 Hz, 2H), 7.13 .br s, 2H), 7.06 .s, 1H), 2.46 .s, 3H). 13C
NMR .100 MHz, DMSO-d) d 192.98, 153.79, 150.13,
136.28, 134.31, 132.32, 130.69, 129.67, 128.66, 125.34,
123.05, 118.70, 118.26, 105.43, 95.72, 92.51, 90.12, 85.54,
30.32. HRMS calcd for C23H15N3O3S: 413.0834; found:
413.0940.
1
1249.8 cm21. H NMR .400 MHz, DMSO-d) d 8.64 .d,
Jˆ5.7 Hz, 2H), 8.25 .s, 1H), 7.67 .dd, Jˆ4.5, 1.5 Hz, 2H),
7.59 .m, 2H), 7.47 .m, 3H), 7.15 .br s, 1H), 7.03 .s, 1H). 13C
NMR .100 MHz, DMSO-d) d 153.97, 149.83, 136.31,
131.67, 131.17, 130.01, 129.69, 128.99, 125.45, 121.78,
120.40, 118.06, 103.92, 96.13, 93.41, 88.37, 86.25. HRMS
calcd for C21H13N3O2: 339.1008; found: 339.1004.
5.5.32. 1-Bromo-3-nitro-4-34-aminophenylethynyl)benzene
336). 1,4-Dibromo-2-nitrobenzene .5.62 g, 20.0 mmol),
bis.triphenylphosphine)palladium dichloride .0.140 g,
0.20 mmol), copper.I) iodide .0.038 g, 0.20 mmol), triethyl-
amine .10.0 mL), THF .10 mL) and 35 .1.170 g,
10.0 mmol) were used following the general procedure for
couplings. The reaction mixture was stirred at room
temperature for 4 h. After solvent removal in vacuo, the
residue was chromatographed on a column of silica
.dichloromethane as eluent) to give a mixture of the desired
product along with its regioisomer as a red solid. The
desired product was isolated from the mixture by a twofold
recrystallization from dichloromethane/hexanes as ®ne
bright red needles .1.561 g, 49% yield). Mp 147±1498C.
IR .KBr) 3457, 3367, 2194, 1623, 1593, 1513, 1550,
1334, 1273, 1136, 834, 817, 528 cm21
.
1H NMR
.400 MHz, CDCl3) d 8.21 .d, Jˆ2.0 Hz), 7.67 .dd, Jˆ8.4,
2.0 Hz), 7.51 .d, Jˆ8.4 Hz), 7.96 .m, AA0 part of AA0XX0

5120
S. M. Dirk et al. / Tetrahedron 57 22001) 5109±5121
pattern, Jˆ8.2, 2.7, 1.9, 0.4 Hz, 2H), 7.93 .m, XX0 part of
AA0XX0 pattern, Jˆ8.2, 2.7, 1.9, 0.4 Hz, 2H), 3.39 .s, 2H).
13C NMR .100 MHz, CDCl3) d 149.27, 147.85, 135.82,
135.12, 133.71, 127.73, 120.62, 118.59, 114.63, 111.09,
100.24, 82.86. HRMS calcd for C14H9N2BrO2: 315.9848;
found: 315.9845.
114.7, 11.1, 98.4, 94.9, 85.3, 85.0. HRMS calcd for
C22H14N2O2: 338.1055; found: 338.1059.
5.5.36. 4-33-Nitro-4-phenylethynylphenylethynyl)benzene-
diazonium tetra¯uoroborate 340). Following the general
diazotization procedure, 39 .0.0676 g, 0.200 mmol) was
treated with NOBF4 .0.025 g, 0.210 mmol) in acetonitrile
.2 mL)/sulfolane .2 mL). The product was precipitated with
ether .20 mL) as ®ne orange±red crystals. The salt was
washed with ether and reprecipitated from DMSO
.0.6 mL) and CH2Cl2 .10 mL) as heavy lustrous red plates
.0.0676 g, 77% yield). IR .KBr) 3101, 2279, 2209, 1576,
5.5.33. 4-32-Nitro-4-phenylethynylphenylethynyl)aniline
337). 36 .0.697 g, 2.20 mmol), bis.triphenylphosphine)-
palladium dichloride .0.062 g, 0.088 mmol), copper.I)
iodide .0.0084 g, 0.044 mmol), triethylamine .10.0 mL)
and ethynylbenzene .0.306 g, 3.00 mmol) were used follow-
ing the general procedure for couplings. The reaction
mixture was stirred at 808C for 2 h. After solvent removal
in vacuo, the residue was chromatographed on a column of
silica with dichloromethane to give red needles of the
desired product .0.72 g, 97% yield), mp 166±1688C. IR
.KBr) 3454, 3381, 3360, 2177, 2197, 1594, 1623, 1539,
.
1540, 1346, 1083, 1034, 840, 764 cm21 1H NMR
.400 MHz, CDCl3/DMSO-d6) d 7.94 .m, AA0 part of
AA0XX0 pattern, Jˆ8.7, 2.4, 1.7, 0.4 Hz, 2H), 7.82 .dd,
Jˆ1.7, 0.4 Hz, 1H), 7.49 .m, XX0 part of AA0XX0 pattern,
Jˆ8.7, 2.4, 1.7, 0.4 Hz, 2H), 7.62 .dd, Jˆ8.1, 1.7 Hz, 1H),
7.56 .dd, Jˆ8.1, 0.4 Hz, 1H), 7.07 .m, AA0 part of
AA0XX0Y pattern, Jˆ7.8, 7.6, 1.8, 1.3, 1.3, 0.6 Hz, 2H),
6.94 .tt, Jˆ7.6, 1.3 Hz, 1H), 6.91 .m, YY0 part of AA0XX0Y
pattern, Jˆ7.8, 7.6, 1.8, 1.3, 1.3, 0.6 Hz, 2H). 13C NMR
.100 MHz, CDCl3/DMSO-d6) d 137.24, 136.97, 136.23,
135.40, 133.72, 133.00, 131.08, 129.96, 129.48, 122.81,
122.75, 120.68, 114.12, 100.47, 98.81, 91.04, 85.57.
1520, 1299, 1342, 1133, 829, 758, 690, 527 cm21 1H
.
NMR .400 MHz, CDCl3) d 8.20 .dd, Jˆ1.6, 0.3 Hz), 7.66
.dd, Jˆ8.2, 1.6 Hz), 7.61 .d, Jˆ8.1 Hz), 7.52±7.57 .m, 2H),
7.36±7.43 .m, 5H), 3.94 .s, 2H). 13C NMR .100 MHz,
CDCl3) d 148.93, 147.81, 135.12, 134.04, 133.76, 131.74,
129.04, 128.49, 127.59, 122.97, 122.18, 118.95, 114.64,
111.29, 100.75, 93.03, 87.05, 83.71. HRMS calcd for
C22H14N2O2: 338.1055; found: 338.1058.
5.5.37. 4-32,5-Dinitro-4-34-aminophenylethynyl)phenyl-
ethynyl)aniline 342). 1,4-Dibromo-2,5-dinitrobenzene12
.0.977 g, 3.0 mmol), bis.triphenylphosphine)palladium
dichloride .0.042 g, 0.06 mmol), copper.I) iodide .0.011 g,
0.06 mmol), triethylamine .5.0 mL), THF .5.0 mL) and 4-
ethynylaniline .0.468 g, 4.00 mmol) were used following
the general procedure for couplings. The reaction mixture
was stirred at room temperature for 12 h. After solvent
removal in vacuo, the residue was sonicated with dichloro-
methane .10 mL) and ®ltered. The ®lter cake was washed
5£ with dichloromethane .10 mL) and dried in vacuo to
afford dark purple crystals of the diamine 42 .0.432 g,
36% yield). Mp .2708C. IR .KBr) 3494, 3387, 2184,
5.5.34. 4-32-Nitro-4-phenylethynylphenylethynyl)benzene-
diazonium tetra¯uoroborate 338). Following the general
diazotization procedure 37 .0.0845 g, 0.250 mmol) was
treated with NOBF4 .0.0322 g, 0.275 mmol) in acetonitrile
.2 mL)/sulfolane .2 mL). The product was precipitated with
ether .12 mL) as dark orange scales. The salt was washed
with ether and reprecipitated from DMSO .0.5 mL) and
CH2Cl2 .20 mL) as lustrous dark orange plates .0.0885 g,
81% yield). IR .KBr) 3103, 2279, 2209, 1576, 1345, 1540,
1
1084, 841, 764 cm21. H NMR .400 MHz, CDCl3/DMSO-
d6, line width of about 1.9 Hz was observed) d 8.78 .d,
Jˆ8.9 Hz, 2H), 8.30 .s, 1H), 8.03 .d, Jˆ8.9 Hz, 2H),
7.85±7.92 .m, 2H), 7.57±7.60 .m, 2H), 7.42±7.44 .m, 3H).
13C NMR .100 MHz, CDCl3/DMSO-d6) d 149.00, 135.46,
134.85, 134.15, 133.31, 132.84, 1.34, 129.13, 128.21, 127.15,
125.66, 121.06, 114.81, 114.25, 94.57, 94.42, 94.11, 86.29.
1
1600, 1400, 1523, 1537, 1308, 1337, 1251, 1136 cm21. H
NMR .400 MHz, DMSO-d6) d 8.37 .s, 2H), 7.27±7.29 .m,
2H), 6.59±6.61 .m, 2H), 5.93 .br s, 4H). 13C NMR
.100 MHz, DMSO-d6) d 151.18, 149.89, 133.67, 129.43,
116.95, 113.66, 106.10, 103.45, 82.23. HRMS calcd for
C22H14N4O4: 398.1015; found 398.1018.
5.5.35. 4-33-Nitro-4-phenylethynylphenylethynyl)aniline
339). 25 .1.208 g, 4.0 mmol), bis.triphenylphosphine)palla-
dium dichloride .0.070 g, 0.10 mmol), copper.I) iodide
.0.019 g, 0.10 mmol), triethylamine .6.0 mL), THF
.6.0 mL) and 35 .0.479 g, 4.10 mmol) were used following
the general procedure for couplings. The reaction mixture
was stirred at room temperature for 15 h. After solvent
removal in vacuo, the residue was chromatographed on a
short column of silica with dichloromethane/hexanes .1:1)
to afford the desired product as an orange solid .0.560 g,
44% yield), mp 175±1778C. IR .KBr) 3303, 2985, 1696,
1587, 1522, 1406, 1314, 1243, 1153, 1060, 839, 757,
5.5.38. 4-32,5-Dinitro-4-34-diazoniophenylethynyl)phenyl-
ethynyl)benzenediazonium
tetra¯uoroborate
343).
Following the general diazotization procedure 42 .0.199 g,
0.500 mmol) was treated with NOBF4 .0.128 g, 1.10 mmol)
in acetonitrile .5.0 mL)/sulfolane .5.0 mL). The product
was precipitated with ether .20 mL). The salt was washed
with ether and reprecipitated from DMSO and CH2Cl2 as
light-sensitive yellow crystals .0.215 g, 72% yield). IR
1
.KBr) 3107, 2291, 1579, 1546, 1342, 1078, 830 cm21. H
NMR .400 MHz, CDCl3/DMSO-d6) d 8.85 .s, 2H), 8.79 .d,
Jˆ9 Hz, 2H), 8.20 .d, Jˆ9 Hz, 2H). 13C NMR .100 MHz,
CDCl3/DMSO-d6) d 150.60, 133.93, 133.83, 133.14,
132.40, 131.75, 117.62, 116.32, 96.91, 91.51.
692 cm21
.
1H NMR .400 MHz, CDCl3) d 8.16 .t,
Jˆ1.0 Hz, 1H), 7.64 .d, Jˆ1.0 Hz, 2H), 7.58±7.61 .m,
2H), 7.34±7.40 .m, 3H), 7.35 .m, AA0 part of AA0XX0
pattern, Jˆ8.0, 2.5, 2.0, 0.4 Hz, 2H), 6.65 .m, XX0 part of
AA0XX0 pattern, Jˆ8.0, 2.5, 2.0, 0.4 Hz, 2H), 3.91 .s, 2H).
13C NMR .100 MHz, CDCl3) 149.4, 147.5, 134.9, 134.3,
133.3, 132.0, 129.3, 128.5, 127.1, 124.9, 122.3, 117.1,
Acknowledgements
We thank the Defense Advanced Research Project Agency,

S. M. Dirk et al. / Tetrahedron 57 22001) 5109±5121
5121
10. .a) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron
Lett. 1975, 50, 4467. .b) Sonogashira, K. In Comprehensive
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the Of®ce of Naval Research and the Army Research Of®ce
for ®nancial support. We also thank Dr I. Chester of FAR
Laboratories for trimethylsilylacetylene.
11. Lamba, J. S.; Tour, J. M. J. Am. Chem. Soc. 1994, 116, 11723±
11736.
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