An effective, orthogonal deprotection strategy for differentially functionalized, linear and Y-shaped oligo phenylene ethynylenes

Article abstract of DOI:10.1016/j.tet.2007.05.006

Several methodologies for the selective deprotection acetylenes have been reported previously. However, as is shown here, they are often not reliable or convenient. Here, an approach is reported that is efficient and general. Use of this approach to synth

Full text of DOI:10.1016/j.tet.2007.05.006

Tetrahedron 63 (2007) 7120–7132
An effective, orthogonal deprotection strategy for differentially
functionalized, linear and Y-shaped oligo phenylene ethynylenes
*
Kusum L. Chandra, Sheng Zhang and Christopher B. Gorman
Department of Chemistry, North Carolina State University, Box 8204, Raleigh, NC 27695-8204, USA
Received 17 January 2007; revised 24 April 2007; accepted 1 May 2007
Available online 6 May 2007
Abstract—Several methodologies for the selective deprotection acetylenes have been reported previously. However, as is shown here, they
are often not reliable or convenient. Here, an approach is reported that is efficient and general. Use of this approach to synthesize several two-
and three-armed oligo(phenylene ethynylene) molecules with differentiated end groups is reported. In addition, preliminary characterization
of the fluorescent properties of some of these molecules and their ability to form self-assembled monolayers (SAMs) is reported.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
is a requirement for the construction of differentiated, nano-
meter-scale architectures composed of particles and is the
long-term goal of our work.
Oligo- and polymeric phenylene ethynylene molecules
(OPEs) have been widely used as molecular wires to study
charge transport in molecular electronics testbeds,1 as rigid
scaffolds in the construction of nanometric architectures,2–4
as dendrimers,5,6 as foldamers,7,8 and as sensors.9–12 Thus,
as we considered new methodologies for nanometric
construction, we were attracted to the body of work describ-
ing their preparation. However, as we sought to adapt this
methodology, we encountered several questions and issues.
In particular, we required a methodology for differential
deprotection of acetylene groups on each end (or ends) of
an OPE molecular structure. Although, as will be described
below, there are several published methodologies that
nominally could serve these requirements, these were
frequently not acceptable for the synthesis of the molecules
described here.
2. Results and discussion
2.1. Linear OPE structures
2.1.1. Differentially functionalized, three-ringed OPE.
Our first goal was to prepare a differentially functionalized,
three-ringed OPE containing thioacetate and isonitrile end
groups. The synthesis of this molecule (10) is shown in
Scheme 1. Compound 2 was prepared as described in the
literature with a yield similar to those previously re-
ported.9,10,16 Palladium catalyzed coupling afforded the
previously unreported compound 3.
Differential deprotection of two ends of an OPE-type struc-
ture has received substantial attention.17–20 Compound 4
has been reported previously several times in the literature,
usually by differentially deprotecting a trimethylsilyl acetyl-
ene in the presence of the TIPS-acetylene,2–4,21–25 although
other methods have been employed.26,27 In our hands, how-
ever, purification of the intermediates produced by this route
was difficult whereas the purification of compound 3 was
much more straightforward. The ynol portion of this mole-
cule can be selectively deprotected in the presence of the
TIPS-acetylene.28 The resulting, mono-deprotected mole-
cule 4 could then be reacted with the known N-(4-iodo-
phenyl)-formamide (5)29,30 to give 6. Use of tetrabutyl
ammonium fluoride followed by palladium/copper catalyzed
coupling with known p-thioacetyl phenyl iodide (8) provided
molecule 9. This molecule could then be dehydrated to
In this paper, we compare methodologies for orthogonal
deprotection of OPE structures and illustrate a route to differ-
entially protected OPE precursors that is most efficient. This
methodology is then used to synthesize series of bi-func-
tional and tri-functional OPEs. Furthermore, it is shown
that this approach tolerates the installation of thioacetate
and isonitrile groups at the ends of the OPEs. Thioacetate
and isonitrile are the functional groups that offer the best
chance to selectively bind to gold and platinum-based nano-
structures, respectively, as shown originally by Wrighton and
Whitesides13,14 and more recently by us.15 Selective binding
* Corresponding author. Tel.: +1 919 515 4252; fax: +1 919 515 8920;
e-mail: chris_gorman@ncsu.edu
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.05.006

K. L. Chandra et al. / Tetrahedron 63 (2007) 7120–7132
7121
OH
H
OH
I
OHex
OH
OHex
OHex
i,
i,
TIPS
OHex
ii
HexO
HexO
HexO
87 %
50%
I
79%
HexO
I
TIPS
TIPS
3
1
2
4
NHCHO
NHCHO
NHCHO
NC
iv, 8
iii
i, 5
v
OHex
OHex
OHex
OHex
93%
55 %
86 %
69 %
HexO
HexO
HexO
HexO
H
TIPS
SAc
SAc
10
6
7
9
Scheme 1. Synthesis of 10. OHex¼O(CH2)5CH3; conditions: (i) Pd2(dba)3$CHCl3, PPh3, CuI, Et3N, 75 ꢀC; (ii) NaOH, toluene, reflux; (iii) TBAF, THF, rt; (iv)
same as (i) except rt; (v) triphosgene, benzyl triethylammonium chloride, Et3N, CH2Cl2.
provide the three-ringed compound with thioacetate and
isonitrile groups (10).
synthesized as shown in Scheme 3. Reaction of aryl iodide
11 with terminal acetylene 7 yielded compound 13 albeit in
poor yield. Deprotection, palladium catalyzed coupling,
An alternate route to intermediate 6 is shown in Scheme 2. It
employs molecule 12, which we obtained in similar yield to
that previously reported.30 This molecule was then coupled
to 11. Both routes require four steps. However, this alternate
route provides 6 in an overall yield of 43% while the route
shown in Scheme 1 provides 6 in an overall yield of 20%.
TIPS
HexO
NHCHO
OHex
+
OHex
HexO
I
I
7
I
OHex
11
OHex
i
38 %
i,
TIPS
69 %
HexO
HexO
HexO
HexO
I
TIPS
11
R
NHCHO
1
OHex
OHex
98 %
TMS
ii,
OHCHN
I
OHCHN
13, R = TIPS
14, R = H
iii, 98%
ii, 99%
5
12
1) iii + 8
2) iv, 76%
HexO
i
HexO
OHCHN
TIPS
HexO
11 + 12
65 %
OHex
AcS
NC
6
OHex
OHex
Scheme 2. Alternate route to 6. Conditions: (i) Pd2(dba)3$CHCl3, PPh3,
CuI, Et3N, 65–70 ꢀC; (ii) Pd2(dba)3$CHCl3, PPh3, CuI, (i-Pr)2EtN, THF
(4:3), rt; (iii) K2CO3, CH3OH/CH2Cl2 (1:1), rt.
16
Scheme 3. Synthesis of 16. Conditions: (i) Pd2(dba)3$CHCl3, PPh3, CuI,
Et3N, 65–70 ꢀC; (ii) TBAF, THF, rt; (iii) Pd2(dba)3$CHCl3, PPh3, CuI,
(i-Pr)2EtN, THF (4:3), rt; (iv) triphosgene, benzyl triethylammonium chlo-
ride, Et3N, CH2Cl2.
2.1.2. Differentially functionalized, four-ringed OPE.
The analogous oligomer containing four rings was

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K. L. Chandra et al. / Tetrahedron 63 (2007) 7120–7132
OHex
OHex
and dehydration of the formamide group provided the four-
ringed oligomer with thioacetate and isonitrile groups (16).
OHCHN
HexO
14
HexO
2.1.3. Differentially functionalized, five-ringed OPE. The
synthesis of five-ringed oligomers are shown in Schemes 4
and 5. For the preparation of molecule 23 (Scheme 4), the
key intermediate, molecule 18 was synthesized in excellent
yield and facilitated differential deprotection of each end
and facile purification. The formamide end group was intro-
duced first, followed by extension using intermediate 11,
introduction of the aryl thioacetate group, and finally, dehy-
dration to form 23.
1) i + 11, 40%
2) ii, 90%
3) iii + 8, 66%
4) iv, 58%
OHex
OHex
HexO
OHex
CN
SAc
For the synthesis of 26 in which all three of the central rings
were substituted with bis-hexyloxy groups, a simple, step-
wise extension sequence was employed. As TIPS deprotec-
tion was most efficient, sequential TIPS deprotections
followed by reaction with 11 or 8 provided the desired com-
pound in seven steps from molecule 7 (Schemes 2, 3 and 5).
HexO
HexO
26
Scheme 5. Synthesis of 26. Conditions: (i) Pd2(dba)3$CHCl3, PPh3, CuI,
Et3N, 75 ꢀC; (ii) TBAF, THF; (iii) same as (i) except Et3N/THF (2:1) as sol-
vent and rt; (iv) triphosgene, benzyl triethylammonium chloride, Et3N,
CH2Cl2.
2.2. Homofunctionalized, three-armed oligo phenylene
ethynylenes
The yield of the tris-coupling of 17 to 1,3,5-tribromobenzene
was modest. This yield undoubtedly could be improved
through the use of 1,3,5-triiodobenzene in this sequence.
However, we chose not to pursue this route as 1,3,5-triiodo-
benzene is significantly more expensive when purchased
commercially and, if one assesses the added effort to prepare
the compound, the overall yield for the sequence is likely to
be little improved. Another notable feature of this sequence
is the illustration that compound 28 (the intermediate as the
result of step ii in the sequence) could be smoothly converted
Prior to implementing a scheme for the orthogonal synthesis
of three-armed oligo phenylene ethynylenes with differenti-
ated end groups, we re-investigated the synthesis of the tris-
thioacetyl functionalized molecule (Scheme 6, compound
29). This molecule31–33 and molecules similar to this in
structure34 have been prepared previously. However, the
route shown in Scheme 6 requires fewer synthetic steps
and provides an overall higher yield.
TIPS
I
OHex
HexO
TIPS
OHex
i
HexO
+
96 %
HO
OH
18
1) ii, 66%
2) i + 5, 67%
17
2
HexO
OHCHN
R
OHex
19, R = TIPS
20, R = H
iii, 96%
1) i + 11, 41%
2) iii, 90%
3) iv + 8, 60%
4) v, 82%
HexO
OHex
CN
SAc
HexO
OHex
23
Scheme 4. Synthesis of 23. Conditions: (i) Pd2(dba)3$CHCl3, PPh3, CuI, Et3N, 75 ꢀC; (ii) NaOH, toluene, reflux; (iii) TBAF, THF; (iv) same as (i) except Et3N/
THF (2:1) as solvent and rt; (v) triphosgene, benzyl triethylammonium chloride, Et3N, CH2Cl2.

K. L. Chandra et al. / Tetrahedron 63 (2007) 7120–7132
7123
R
their use, we did not observe any problem of this type using
this route.
TIPS
2.3. Heterofunctionalized, three-armed oligo phenylene
ethynylenes
Br
i
+
3
We then sought to prepare three-armed oligo phenylene
ethynylenes such as molecule 29 but with differentiated
end groups. Such molecules are, to our knowledge, unre-
ported in the literature. The idea of differentiating phenyl
acetylenes around a 1,3,5-trihalobenzene core, however,
does have some precedent in the literature. Indeed, our first
attempt at this chemistry involved the selective deprotection
of TMS-acetylene groups in the presence of a TIPS-acetyl-
ene. The synthesis and selective deprotection of TMS-
acetylene groups in the presence of TIPS-acetylene had
been reported previously by Onitsuka et al.36 Following
this protocol (Scheme 7), we attempted to prepare the mono-
TIPS-protected triethynyl benzene via molecule 30.37 How-
ever, in our hands, we could not purify molecule 30 away
from 31 that was statistically formed. The problem of sepa-
ration of aromatic halides and their corresponding TMS-38
or TIPS-protected39 ethynylated compounds has been men-
tioned previously by others.38 This purification problem be-
came exacerbated in subsequent steps, and ultimately this
method was abandoned. Given this problem, we turned to re-
ports by Rodriguez et al.35 and Wang et al.19 in which formal
removal of acetone as a protecting group was accomplished
in the presence of TMS-protected acetylenes (e.g., conver-
sion of 32 to 33). This route also was problematic in our
hands, resulting in substantial amounts of 1,3,5-triethynyl
benzene as a side product, presumably due to removal of
the TMS groups competitively with the acetone.
41 %
Br
Br
17
R
R
27, R = TIPS
28, R = H
ii, 97%
iii + 3 eq. 8, 70%
AcS
SAc
29
We devised a modified approach to circumvent these prob-
lems (Scheme 8). Employing TIPS-protected acetylenes
rather than TMS-protected acetylenes allowed the selective
removal of acetone from the intermediate to give 36. The
route to molecule 36 provided high yields and no difficulties
in purification.
SAc
Scheme 6. Synthesis of 29. Conditions: (i) Pd2(dba)3$CHCl3, PPh3, CuI,
Et3N, 65–70 ꢀC; (ii) TBAF, THF; (iii) same as (i) except rt.
to 29 in good yield. Although concerns have been expressed
previously in the literature35 that oxidative coupling or poly-
merization of monofunctionalized acetylenes could limit
The intermediate molecule 36 could then be used to prepare
AAB-type three-armed phenyl ethynylenes. The example
TIPS
Br
Br
i,
TIPS
+
Br
Br
Br
Br
TIPS
TIPS
TIPS
30
31
TMS
TMS
ii, 72 %
iii, 85 %
iv
+
OH
TMS
TMS
32
33
Scheme 7. Ineffective methods for orthogonal deprotection to form 33. Conditions: (i) Pd2(dba)3$CHCl3, PPh3, CuI, Et3N, 65–70 ꢀC; (ii) HC^CC(CH3)2OH,
Pd2(dba)3$CHCl3, PPh3, CuI, pyridine, Et3N, 100 ꢀC; (iii) 2 equiv HC^CTMS, Pd(PPh3)2Cl2, Et3N, 60 ꢀC; (iv) NaOH, toluene, reflux.

7124
K. L. Chandra et al. / Tetrahedron 63 (2007) 7120–7132
TIPS
for several of the differentially functionalized, linear
compounds. The UV absorption and emission maxima in-
crease with molecular length. The quantum yield doubles
between the three-ring compound 10 and the four-ring com-
pound 16 but then is similar to the five-ring compounds 23
and 26.
Br
1) i, 72%
2) ii, 97%
3) iii, 90%
Br
Br
TIPS
H
36
2.5. Self-assembled monolayers
Scheme 8. Synthesis of 36. Conditions: (i) Pd2(dba)3$CHCl3, PPh3, CuI,
Et3N, pyridine, HC^CC(OH)(CH3)2, 100 ꢀC; (ii) same as (i) except with
2 equiv TIPS-acetylene and no pyridine; (iii) NaOH, toluene, reflux.
Self-assembled monolayers (SAMs) composed of com-
pounds 10 and 23 were prepared on both gold and platinum
surfaces. Film thickness as measured by ellipsometry (Table 2)
agreed well with calculated molecular lengths indicating
reasonably high coverage SAMs were formed. X-ray photo-
electron spectroscopy also indicated the presence of these
molecules on both surfaces. Although it was hoped that dif-
ferences in the S2p and N1s binding energies would indicate
a preference for nitrile versus thiol binding when SAMs on
gold and platinum were compared, little difference was ob-
served. Indeed, in prior work, little difference in the binding
energy between free and bound sulfur or nitrogen in SAMs
was observed by XPS. Moreover, S2p binding energies re-
ported in the literature for thiol-bound SAMs vary several
electron volts for different molecules. Rather, the dipole
moment of the molecule and, more specifically, the charge
distribution across it appear to be more significant to the
XPS binding energy.40 Further work to determine the rela-
tive affinity of the thiol versus the isonitrile on gold com-
pared to platinum is in progress and will be reported
separately.
presented (Scheme 9) illustrates the method used to arrive at
the three-armed phenyl ethynylene in which two arms termi-
nate with thioacetate group and the third arm terminates with
an isonitrile group (40). Although the palladium coupling
chemistry proceeded in only modest yield, there were no
problems with purification and isolation of the desired
compounds.
R
TIPS
i + 5
90 %
R
TIPS
H
36
NHCHO
ii, 89%
37, R = TIPS
38, R = H
1) iii + 2 eq. 8, 52%
2) iv, 38%
3. Conclusions
It has been determined that the selective deprotection of a
dimethyl-ynol in the presence of TIPS-acetylene groups is
the most efficient route to prepare two- and three-armed,
oligo(phenylene ethynylene) molecules with differentiated
end groups. This strategy could be employed for the rela-
tively efficient synthesis of several new compounds.
SAc
4. Experimental
4.1. General
AcS
NC
Molecules 1,41 5,30 8,42,43 11,23 12,30 3235 and 3335 were pre-
pared as described previously and determined to have H
40
1
Scheme 9. Synthesis of 40. Conditions (i) Pd2(dba)3$CHCl3, PPh3, CuI,
Et3N, 65–70 ꢀC; (ii) TBAF, THF; (iii) same as (i) except rt; (iv) triphosgene,
benzyl triethylammonium chloride, Et3N, CH2Cl2.
NMR and 13C NMR spectra consistent with those reported.
4.2. Absorption and fluorescence measurements
In preparation for the synthesis of larger, three-armed mole-
cules, molecule 43 was prepared as shown in Scheme 10.
This molecule can serve as a starting material for similar
subsequent chemistry. Specifically, the orthogonal deprotec-
tion of the dimethyl-ynol and TIPS-acetylene groups should
afford molecules with differentiated end groups as shown
above.
Absorption spectra were recorded on a Hewlett Packard
Diode array UV–vis–NIR Spectrometer. Quantum-corrected
emission spectra were measured with an LS 50B lumines-
cence spectrometer (Perkin–Elmer). Solutions for fluores-
cence measurements were prepared inside an anerobic
glovebox at specific concentrations in THF distilled over
Na. The solutions were introduced into a quartz cuvette
equipped with a Teflon cap to minimize contact with air.
The emission spectra were obtained under the excitation
of 354 nm with a slit width of 2.5 nm. Four-sided quartz
cells with a length of 1 cm were used, and the detector
2.4. Fluorescence properties
Table 1 contains the absorbance maximum, fluorescence
maximum, and quantum yield (relative to quinine bisulfate)

K. L. Chandra et al. / Tetrahedron 63 (2007) 7120–7132
7125
TIPS
TIPS
TIPS
Br
i
+
Br
90 %
OH
34
41
17
OH
TIPS
TIPS
I
ii
68 %
+
42
OH
65 %
i
TIPS
TIPS
OH
43
Scheme 10. Synthesis of 43. Conditions: (i) Pd2(dba)3$CHCl3, PPh3, CuI, Et3N, 70 ꢀC; (ii) NaOH, toluene, reflux.
was arranged perpendicular to the incident beam. Photolu-
minescence quantum yields were calculated against quinine
sulfate in 1 N sulfuric acid as a standard.
Table 1. Fluorescence quantum yields (F) of compounds 10, 16, 23, and 26
in anhydrous THF with maximum wavelengths of UV absorption and
emissiona
Compound
10
16
23
26
4.3. Preparation of self-assembled monolayers
lmax (nm)
Absorption
Emission
380
438
398
443
398
438
406
453
Polycrystalline gold films were purchased from EMF. Pt
films were deposited onto glass substrates by first deposition
of 5 nm Cr and a followed deposition of 100 nm of Pt. The
gold substrates were cleaned with ‘piranha’ solution (7:3
H2SO4/H2O2), washed with water and ethanol and followed
by the sonication in ethanol for 10 min and rinse with etha-
nol. Caution! ‘piranha’ solution should be handled carefully
because of its violent reactivity with organic molecules. The
Pt substrates were cleaned by soaking in sulfuric acid for
20 min followed by the sonication in ethanol for 10 min,
which were then rinsed with water and ethanol and dried
over nitrogen. SAMs of 10, 16, 23, and 26 were formed on
Pt in 0.5 mM THF solutions for 2 days. SAMs on Au were
prepared using the same procedure except that the thioacetyl
group was cleaved by the addition of 10 mL NH4OH to the
sample solutions, which was incubated for 20 min.
F
0.38
0.73
0.75
0.76
a
All solutions were prepared and transferred into the fluorescence cuvette
in the dry box.
Table 2. Film thicknesses and XPS data for SAMs of compounds 10 and 23
on Au and Pt surfaces
Molecular lengtha Thicknessb (A) Binding energyc (eV)
˚
SAM
C1s O1s S2p N1s
10 on Au 21.0
23 on Au 34.7
10 on Pt 22.9
23 on Pt 36.2
19.5
31.6
22.1
34.4
284.6 532.3 164.2 398.4
284.5 532.1 164.4 400.1
284.5 532.1 163.7 398.9
284.1 531.7 164.2 399.5
a
Calculated from AM1 geometry optimized molecular structures.
Measured by ellipsometry.
Measured by X-ray photoelectron spectroscopy.
b
c

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K. L. Chandra et al. / Tetrahedron 63 (2007) 7120–7132
4.4. Ellipsometry measurements
procedure for Sonogashira coupling was followed using
TIPS-acetylene (1.05 equiv) and a reaction time of 48 h at
70 ꢀC. The crude compound was purified by flash column
chromatography in ethyl acetate/hexanes (80:20) to yield
pure compound 3. Yield 87% (640 mg); mp 43 ꢀC; IR
The ellipsometric measurements were recorded using a vari-
able angle spectroscopic ellipsometer (J. A. Woollam, Inc.,
Lincoln, NE). He–Ne laser light was incident at 70ꢀ on the
sample. The experimental polarization angles were used to
determine film thickness. All the thickness were calculated
based on isotropic film models in which the complex refrac-
tive index is described as a scalar, n¼n+ik. The absorption
index (k) was set to zero, while n was estimated to be 1.55
and 1.3 for SAMs on Au and Pt, respectively.
1
(thin film): 3405, 2893, 2864, 1498, 1382, 1216 cmꢁ1; H
NMR (CDCl3, 300 MHz): 6.88 (s, 1H), 6.83 (s, 1H), 3.94
(m, 4H), 2.04 (s, 1H, –OH), 1.77 (m, 4H), 1.62 (s, 6H),
1.47 (m, 4H), 1.31 (m, 8H), 1.13 (s, 21H), 0.89 (m, 6H);
13C NMR (CDCl3, 75 MHz): 154.4, 153.5, 117.7, 116.7,
114.1, 113.5, 103.0, 99.1, 96.5, 78.8, 69.7, 69.4, 66.0,
31.9, 31.8, 31.6, 29.6, 29.5, 26.1, 25.9, 22.8, 18.9, 14.3,
11.6. Mass calculated for (M+) C34H56O3Si 540.3999, found
(HRMS-FAB) 540.3965.
4.5. XPS measurements
XPS spectra were recorded on a Kratos Axis Ultra X-ray Pho-
toemission Spectrometer using an Al ka source monochrom-
atized at 1486.6 eV. The radiation was generated at 10 mA
under 15 kV. Pass energy of 160 and 20 eV was used for sur-
vey and regional spectrum, respectively. The core level bind-
ing energies were corrected by a rigid shift to bring the Au
4f7/2 and Pt 4f7/2 peaks to 84 and 71.3 eV, respectively.
4.8. General procedure for base-promoted deprotection
of trialkyl-silyl acetylenes
Trialkyl-silyl acetylene (2.2 mmol) was taken in dry toluene
(20 mL) under nitrogen atmosphere. Powdered sodium hy-
droxide (140 mg, 3.3 mmol) was added to the reaction
mixture. The reaction mixture was refluxed for 24 h under
nitrogen. The reaction mixture was cooled to room temper-
ature and filtered off the solid residue. The filtrate was
evaporated and residue purified over flash column chromato-
graphy.
4.6. 4-(2,5-Bis-hexyloxy-4-iodo-phenyl)-2-methyl-but-3-
yn-2-ol (2)
Inside a N2-filled dry box, 1 (2.5 g, 4.7 mmol), tris(dibenzyl-
ideneacetone)bispalladium(146 mg,0.141 mmol),triphenyl-
phosphine (123 mg, 0.47 mmol), and copper iodide (90 mg,
0.47 mmol) were weighed in an oven dried Schlenk flask.
Triethylamine (12 mL) and pyridine (4 mL) were added to
the reaction mixture and stirred for 10 min followed by
the addition of 2-methyl-3-butyn-2-ol (477 mL, 4.7 mmol).
The reaction mixture was stirred for 48 h at 75 ꢀC. The reac-
tion mixture was cooled to room temperature and filtered
through a small silica gel plug and washed with dichlorome-
thane. The filtratewas evaporatedand theresiduewas purified
by flash column chromatography using a mixture of ethyl
acetate/hexanes (20:80) to yield 1.1 g (50%) of 2. Mp
42 ꢀC; IR (thin film): 3403, 2930, 2863, 1618, 1465,
1024 cmꢁ1; 1H NMR (CDCl3, 300 MHz): 7.24 (s, 1H), 6.78
(s, 1H), 3.91 (t, J¼6.3 Hz, 4H), 2.27 (s, 1H, –OH), 1.76 (m,
4H), 1.61 (s, 6H), 1.48 (m, 4H), 1.34 (m, 8H), 0.89 (m, 6H);
13C NMR (CDCl3, 75 MHz): 154.5, 151.9, 123.9, 116.3,
113.2, 98.8, 87.6, 78.4, 70.3, 69.9, 65.9, 31.8, 31.7, 31.6,
29.5, 29.3, 25.9, 25.9, 22.8, 22.8, 14.4. Mass calculated for
(M+) C23H35IO3 486.1631, found (HRMS-FAB) 486.1617.
4.8.1. (4-Ethynyl-2,5-bis-hexyloxy-phenylethynyl)-triiso-
propyl-silane (4). This compound has been reported previ-
ously,44 but its synthesis and characterization have not. The
general procedure for base-promoted deprotection of tri-
alkyl-silyl acetylenes was followed using molecule 3. The
compound was purified by flash chromatography using ethyl
acetate/hexanes (15:85) to yield pure compound 4. Yield
79% (780 mg); mp 38 ꢀC; IR (thin film): 2936, 2863, 2144,
1594, 1496, 1219 cmꢁ1; 1H NMR (CDCl3, 300 MHz): 6.95
(s, 2H), 3.95 (m, 4H), 3.21 (s, 1H), 1.78 (m, 4H), 1.47 (m,
4H), 1.31 (m, 8H), 1.13 (s, 21H), 0.89 (m, 6H); 13C NMR
(CDCl3, 75 MHz): 154.3, 154.1, 117.8, 117.3, 114.8,
112.8, 102.9, 96.8, 82.3, 80.2, 69.9, 69.4, 31.8, 31.7, 29.6,
29.3, 26.0, 25.8, 22.8, 22.8, 18.9, 14.3, 14.2, 11.5. Anal.
Calcd for C31H50O2Si: C, 77.12; H, 10.44; Si, 5.82; O,
6.63. Found: C, 76.75; H, 10.15. Mass calculated for (M+)
C31H50O2Si 482.3580, found (HRMS-FAB) 482.3571.
4.9. N-(4-{2,5-Bis-hexyloxy-4-[(triisopropylsilanyl)-
ethynyl]-phenylethynyl}-phenyl)-formamide (6)
4.7. General procedure for Sonogashira coupling
The general procedure for Sonogashira coupling was fol-
lowed using molecules 4 and 5. Alternatively, it was pre-
pared by the coupling of molecules 11 and 12 using the
same general procedure of Sonogashira coupling in 65%
yield after purification. The crude compound was purified
by flash column chromatography by using ethyl acetate/
hexanes (60:40) to yield the pure compound 6. Yield 86%
(483 mg); mp 76 ꢀC; IR (thin film): 2893, 2864, 1691,
Inside a N2-filled dry box, aryl iodide (1 mmol), tris(dibenz-
ylideneacetone)bispalladium (31 mg, 0.03 mmol), triphe-
nylphosphine (26 mg, 0.10 mmol), copper iodide (19 mg,
0.01 mmol), and terminal acetylene (1 mmol) were weighed
in an oven dried Schlenk flask. Triethylamine (10 mL) was
added to the reaction mixture. The reaction mixture was
stirred for 48 h at 75 ꢀC. The reaction mixture was cooled
to room temperature and filtered through a small silica gel
plug and washed with dichloromethane. The filtrate was
evaporated and the residue was purified by flash column
chromatography.
1519, 1408, 1215 cmꢁ1 1H NMR (CDCl3, 300 MHz):
;
8.69 (d, J¼11.7 Hz, 0.36H), 8.34 (s, J¼11.7 Hz, 0.68H),
8.31 (d, J¼1.5 Hz, 0.22H), 7.49–7.40 (m, 4H), 7.20 (s,
0.15H), 7.01 (d, J¼8.7 Hz, 0.89H), 6.87 (s, 2H), 3.96–3.87
(m, 4H), 1.76–1.67 (m, 4H), 1.47–1.42 (m, 4H), 1.28–1.22
(m, 8H), 1.08 (s, 21H), 0.84 (m, 6H); 13C NMR (CDCl3,
75 MHz): 162.4, 159.1, 154.5, 153.5, 137.0, 136.7, 133.2,
4.7.1. 4-{2,5-Bis-hexyloxy-4-[(triisopropylsilanyl)-ethyn-
yl]-phenyl}-2-methyl-but-3-yn-2-ol (3). The general

K. L. Chandra et al. / Tetrahedron 63 (2007) 7120–7132
7127
132.6, 120.5, 119.9, 119.7, 118.3, 117.9, 116.4, 114.3, 114.1,
113.9, 103.1, 96.9, 96.7, 94.4, 93.9, 86.7, 86.2, 69.9, 69.5,
31.9, 31.8, 29.6, 29.5, 26.0, 25.9, 22.8, 18.9, 14.3, 14.2,
11.5. Mass calculated for (M+) C38H55NO3Si 601.3951,
found (HRMS-FAB) 601.3961.
in 2 mL of dry dichloromethane was added dropwise. The
reaction mixture was stirred for 7 h and allowed to warm
gradually to room temperature. The reaction mixture was
taken in water and extracted with dichloromethane. The or-
ganic layer was washed with water and brine, respectively.
The organic layer was dried over sodium sulfate before dry-
ing it under vacuum. The crude compound was purified over
column chromatography.
4.10. General procedure for fluoride-promoted depro-
tection of trialkyl-silyl acetylenes
Trialkyl-silyl acetylene (1 mmol) was taken in dry THF
(6 mL) under nitrogen atmosphere and added a 1.0 M solu-
tion of tetrabutyl ammonium fluoride (1.4 mL, 1.4 mmol).
The reaction mixture was stirred overnight, extracted with
ethyl acetate, and washed with brine. The organic layer
was dried over sodium sulfate before drying it under vac-
uum. The crude compound was purified over flash column
chromatography.
4.12.1. Thioacetic acid S-{4-[2,5-bis-hexyloxy-4-(4-iso-
cyano-phenylethynyl)-phenylethynyl]-phenyl} ester
(10). General procedure for phosgene-mediated dehydration
of formamide to isonitrile was followed using molecule 9
(150 mg). The crude compound was purified by flash col-
umn chromatography using ethyl acetate/hexanes (20:80)
to yield pure compound 10. Yield 69% (100 mg); mp
80 ꢀC; IR (thin film): 2930, 2862, 2120, 1709, 1508,
1
1216 cmꢁ1; H NMR (CDCl3, 300 MHz): 7.48 (dd, J¼8.1,
4.10.1. N-[4-(4-Ethynyl-2,5-bis-hexyloxy-phenyl-
ethynyl)-phenyl]-formamide (7). The general procedure
for fluoride-promoted deprotection of trialkyl-silyl acetyl-
enes was followed using molecule 6 (1.2 g). Yield 93%
(830 mg); mp 74 ꢀC; IR (thin film): 3285, 2930, 1689,
6.0 Hz, 4H), 7.31 (dd, J¼13.5, 8.4 Hz, 4H), 6.95 (s, 1H),
6.94 (s, 1H), 3.96 (m, 4H), 2.37 (s, 3H), 1.78 (m, 4H),
1.47 (m, 4H), 1.29 (m, 8H), 0.83 (m, 6H); 13C NMR
(CDCl3, 75 MHz): 193.6, 165.9, 154.0, 153.9, 134.4, 132.6,
132.3, 128.3, 126.6, 125.1, 124.8, 117.0, 114.5, 113.5, 94.6,
93.4, 89.1, 87.7, 69.8, 69.7, 31.8, 30.5, 29.5, 25.9, 22.8, 14.2.
Mass calculated for (M+) C37H39NO3S 577.2651, found
(HRMS-FAB) 577.2665.
1520, 1407, 1275 cmꢁ1 1H NMR (CDCl3, 300 MHz):
;
8.69 (d, J¼9.6 Hz, 0.38H), 8.32 (s, 0.68H), 8.24 (br,
0.20H), 7.50–7.41 (m, 4H), 7.20 (s, 0.25H), 7.01 (d,
J¼6.9 Hz, 0.87H), 6.91 (s, 2H), 3.93 (m, 4H), 3.28 (s, 1H),
1.75 (m, 4H), 1.44 (m, 4H), 1.27 (m, 8H), 0.83 (m, 6H);
13C NMR (CDCl3, 75 MHz): 162.3, 159.0, 154.3, 153.6,
137.1, 133.3, 132.6, 120.4, 119.7, 118.3, 117.9, 117.0,
114.8, 114.5, 112.9, 112.7, 94.7, 94.1, 86.4, 85.8, 82.6,
82.5, 80.2, 69.8, 31.7, 31.7, 29.4, 29.3, 25.9, 25.8, 22.8,
22.8, 14.2. Anal. Calcd for C29H35NO3: C, 78.17; H, 7.92;
N, 3.14; O, 10.77. Found: C, 78.44; H, 7.97; N, 3.27.
4.13. N-[4-(4-{2,5-Bis-hexyloxy-4-[(triisopropylsilanyl)-
ethynyl]-phenylethynyl}-2,5-bis-hexyloxy-phenyl-
ethynyl)-phenyl]-formamide (13)
The general procedure for Sonogashira coupling was fol-
lowed using molecules 7 and 11. The crude compound was
purified by flash column chromatography using ethyl ace-
tate/hexanes (60:40) to yield pure compound 13. Yield
38% (170 mg); mp 54 ꢀC; IR (thin film): 2930, 2863,
4.11. Thioacetic acid S-{4-[4-(4-formylamino-phenyl-
ethynyl)-2,5-bis-hexyloxy-phenylethynyl]-phenyl} ester
(9)
1692, 1594, 1213 cmꢁ1 1H NMR (CDCl3, 300 MHz):
;
8.75 (d, J¼10.8 Hz, 0.5H), 8.36 (s, 0.6H), 8.24 (d,
J¼11.1 Hz, 0.4H), 7.51 (m, 4H), 7.40–7.32 (m, 2H), 7.07
(d, J¼7.8 Hz, 0.8H), 6.99 (s, 2H), 6.95 (s, 2H), 3.92–4.03
(m, 8H), 1.84 (m, 8H), 1.51 (m, 8H), 1.33 (m, 16H), 1.14
(s, 21H), 0.89 (m, 12H); 13C NMR (CDCl3, 75 MHz):
162.1, 159.0, 154.5, 153.8, 153.7, 153.4, 137.0, 136.6,
133.2, 132.6, 120.6, 119.9, 119.7, 118.4, 118.1, 117.2, 117.1,
116.9, 116.7, 114.6, 114.5, 114.4, 114.2, 114.2, 114.1, 113.8,
103.2, 96.8, 96.7, 94.6, 94.1, 91.9, 91.8, 91.5, 91.4, 86.7,
86.2, 70.0, 69.9, 69.7, 69.4, 31.9, 31.8, 31.8, 29.6, 29.5, 29.4,
26.0, 25.9, 25.8, 22.8, 18.9, 14.2, 14.2, 11.6. Mass calculated
for (M+) C58H83NO5Si 901.6041, found (HRMS-FAB)
901.6060.
The general procedure for Sonogashira coupling was fol-
lowed using molecules 7 and 8, but at room temperature for
24 h. Yield 55% (184 mg); mp 92 ꢀC; IR (thin film): 2929,
1693, 1592, 1519, 1414 cmꢁ1
;
1H NMR (CDCl3,
300 MHz): 8.75 (d, J¼11.4 Hz, 0.5H), 8.37 (d, J¼1.8 Hz,
0.7H), 8.04 (d, J¼11.1 Hz, 0.5H), 7.56–7.47 (m, 6H),
7.40–7.37 (m, 2H), 7.06 (d, J¼8.7 Hz, 0.6H), 6.99 (m, 2H),
4.02 (m, 4H), 2.43 (s, 3H), 1.84 (m, 4H), 1.54 (m, 4H),
1.35 (m, 8H), 0.89 (m, 6H); 13C NMR (CDCl3, 75 MHz):
194.1, 162.5, 159.4, 153.9, 153.7, 153.7, 137.3, 136.9, 134.4,
133.2, 132.6, 132.3, 128.1, 125.1, 119.8, 119.6, 118.3, 117.1,
116.9, 114.5, 113.6, 94.9, 94.2, 88.1, 86.0, 69.8, 31.8, 30.5,
29.5, 25.9, 22.8, 14.3. Mass calculated for (M+)
C37H41NO4S 595.2756, found (HRMS-FAB) 595.2751.
4.14. N-{4-[4-(4-Ethynyl-2,5-bis-hexyloxy-phenyl-
ethynyl)-2,5-bis-hexyloxy-phenylethynyl]-phenyl}-
formamide (14)
4.12. General procedure for phosgene-mediated dehy-
dration of formamide to isonitrile
The general procedure for fluoride-promoted deprotection
was employed on molecule 13. The crude compound was
purified by flash chromatography using ethyl acetate/hex-
anes (60:40) to yield pure compound 14. Yield 99%
(140 mg); mp 98 ꢀC; IR (thin film): 3284, 2930, 2863,
Formamide (0.26 mmol) and triphosgene (38 mg, 0.13
mmol) were weighed in an oven dried Schlenk flask. The
flask was evacuated and back filled with nitrogen (two
times). To this was added dry dichloromethane (5 mL),
cooled to 0 ꢀC, and added triethylamine (2 mL). A solution
of benzyltriethyl ammonium chloride (6.0 mg, 0.026 mmol)
1691, 1599, 1419, 1275, 1022 cmꢁ1 1H NMR (CDCl3,
;
300 MHz): 8.75 (d, J¼11.4 Hz, 0.5H), 8.39 (d, J¼1.8 Hz,
0.7H), 7.88 (d, J¼11.4 Hz, 0.5H), 7.52 (m, 3H), 7.27 (m,

7128
K. L. Chandra et al. / Tetrahedron 63 (2007) 7120–7132
1H), 7.06 (d, J¼8.9 Hz, 0.5H), 6.99 (m, 4H), 4.01 (m, 8H),
3.34 (s, 1H), 1.84 (m, 8H), 1.51 (m, 8H), 1.34 (m, 16H),
0.89 (m, 12H); 13C NMR (CDCl3, 75 MHz): 162.2, 159.1,
154.3, 153.7, 153.7, 153.5, 137.0, 136.7, 133.2, 132.6, 120.5,
119.8, 119.7, 118.4, 118.1, 117.2, 117.2, 115.1, 114.3, 114.0,
112.7, 94.7, 94.2, 91.7, 91.4, 86.7, 86.1, 82.6, 80.2, 69.9,
69.8, 31.6, 31.7, 29.5, 29.4, 29.3, 25.9, 25.8, 25.8, 22.8,
22.8, 14.2. Anal. Calcd for C49H63NO5: C, 78.89; H, 8.51;
N, 1.88; O, 10.72. Found: C, 78.52; H, 8.51; N, 1.85.
88.0, 78.6, 69.7, 69.6, 65.8, 31.8, 31.6, 29.5, 25.9, 25.9,
22.8, 18.8, 14.2, 14.2, 11.5. Anal. Calcd for C42H60O3Si:
C, 78.70; H, 9.43; Si, 4.38; O, 7.49. Found: C, 78.14; H, 9.25.
4.18. N-[4-(2,5-Bis-hexyloxy-4-{4-[(triisopropylsilanyl)-
ethynyl]-phenylethynyl}-phenylethynyl)-phenyl]-form-
amide (19)
Compound 18 (615 mg) was subjected to the general proce-
dure for base-promoted deprotection of trialkyl-silyl acet-
ylenes. The compound was purified by flash column
chromatography using ethyl acetate/hexanes (20:80) to yield
the intermediate for the next step. Yield 66% (370 mg); IR
(thin film): 3307, 2931, 2863, 2361, 2149, 1502,
4.15. Thioacetic acid S-(4-{4-[2,5-bis-hexyloxy-4-(4-iso-
cyano-phenylethynyl)-phenylethynyl]-2,5-bis-hexyloxy-
phenylethynyl}-phenyl) ester (16)
The general procedure for Sonogashira coupling was fol-
lowed using 14 and 8 (1.0 equiv) and a reaction time of
48 h at 70 ꢀC. The crude compound was purified by flash col-
umn chromatography using ethyl acetate/hexanes (60:40) to
yield pure 15. Yield 48% (42 mg); 1H NMR (CDCl3,
300 MHz): 8.75 (d, J¼11.4 Hz, 0.5H), 8.38 (d, J¼1.8 Hz,
0.7H), 7.88 (d, J¼11.4 Hz, 0.5H), 7.57–7.48 (m, 6H),
7.40–7.32 (m, 2H), 7.06 (d, J¼8.9 Hz, 0.6H), 7.01 (m, 4H),
4.04 (m, 8H), 2.44 (s, 3H), 1.85 (m, 8H), 1.54 (m, 8H),
1.35 (m, 16H), 0.89 (m, 12H). This molecule was then taken
and subjected to the general procedure for phosgene-medi-
ated dehydration of formamide to isonitrile was followed us-
ing the molecule 15. The crude compound was purified by
flash column chromatography using ethyl acetate/hexanes
(20:80) to yield pure 16. Yield 76% (32 mg); mp 84 ꢀC; IR
1217 cmꢁ1 1H NMR (CDCl3, 300 MHz): 7.39 (s, 4H),
;
6.93 (s, 1H), 6.91 (s, 1H), 3.94 (m, 4H), 3.29 (s, 1H), 1.77
(m, 4H), 1.45 (m, 4H), 1.29 (m, 8H), 1.08 (s, 21H), 0.85
(m, 6H); 13C NMR (CDCl3, 75 MHz): 154.3, 153.7, 132.1,
131.5, 123.5, 123.4, 117.9, 117.0, 114.5, 113.0, 106.9, 94.8,
93.0, 87.8, 82.6, 80.1, 69.8, 69.8, 31.8, 31.7, 29.4, 29.3, 25.9,
25.8, 22.8, 22.8, 18.8, 14.2, 11.5. This intermediate com-
pound was taken and subjected to Sonogashira coupling us-
ing 5 (1.0 equiv) following the general procedure. The
crude compound was purified by flash column chromato-
graphy using ethyl acetate/hexanes (50:50) to yield the
pure compound 19. Yield 67% (300 mg); IR (thin film):
3281, 2938, 2864, 2211, 2153, 1691, 1519, 1216 cmꢁ1; 1H
NMR (CDCl3, 300 MHz): 8.68 (d, J¼11.4 Hz, 0.18H),
8.34 (br s, 0.4H), 7.50–7.42 (m, 4H), 7.39 (s, 3H), 7.19 (s,
1H), 6.99 (d, J¼8.7 Hz, 1H), 6.94 (s, 2H), 3.96 (t, J¼
6.3 Hz, 4H), 1.78 (m, 4H), 1.50 (m, 4H), 1.29 (m, 8H),
1.07 (s, 21H), 0.84 (m, 6H); 13C NMR (CDCl3, 75 MHz):
161.8, 158.8, 153.8, 153.8, 136.9, 133.3, 132.7, 132.1, 131.5,
123.5, 120.6, 119.9, 119.7, 118.4, 116.9, 114.3, 114.0, 113.8,
106.9, 94.8, 94.7, 94.1, 93.0, 87.9, 86.7, 86.1, 69.8, 31.8,
29.5, 25.9, 22.8, 18.8, 14.2, 11.5. Mass calculated for (M+)
C46H59NO3Si 701.4264, found (HRMS-FAB) 701.4274.
1
(thin film): 2928, 2361, 1710, 1511, 1276, 1217 cmꢁ1; H
NMR (CDCl3, 300 MHz): 7.56–7.52 (m, 4H), 7.41–7.35
(m, 4H), 7.01 (m, 4H), 4.02 (m, 8H), 2.44 (s, 3H), 1.85 (m,
8H), 1.53 (m, 8H), 1.35 (m, 16H), 0.89 (m, 12H); 13C
NMR (CDCl3, 75 MHz): 193.7, 165.8, 154.0, 153.9, 153.7,
153.6, 134.4, 132.6, 132.3, 128.2, 126.6, 125.2, 124.9,
117.2, 115.2, 114.6, 113.9, 113.1, 94.3, 93.2, 92.0, 91.6,
89.2, 87.9, 69.9, 69.9, 69.7, 69.6, 31.8, 31.8, 30.5, 29.4,
25.9, 25.8, 22.8, 14.2. Mass calculated for (M+)
C37H67NO5S 877.4740, found (HRMS-FAB) 877.4752.
4.19. N-{4-[4-(4-Ethynyl-phenylethynyl)-2,5-bis-hexyl-
oxy-phenylethynyl]-phenyl}-formamide (20)
4.16. (2-(4-Ethynylphenyl)ethynyl)triisopropylsilane
(17)
The compound 19 was deprotected by following the general
procedure of fluoride-promoted deprotection of trialkyl-silyl
acetylenes. The crude compound was purified by flash col-
umn chromatography using ethyl acetate/hexanes (50:50)
to yield pure 20. Yield 96% (215 mg); IR (thin film):
3288, 2930, 2864, 2205, 2108, 1691, 1598, 1214 cmꢁ1; 1H
NMR (CDCl3, 300 MHz): 8.68 (d, J¼11.4 Hz, 0.38H),
8.34 (br s, 0.53H), 7.50–7.42 (m, 4H), 7.41 (s, 3H), 7.19
(s, 1H), 6.99 (d, J¼8.7 Hz, 1H), 6.94 (s, 2H), 3.96 (t,
J¼6.3 Hz, 4H), 3.12 (s, 1H), 1.78 (m, 4H), 1.46 (m, 4H),
1.29 (m, 8H), 0.83 (m, 6H); 13C NMR (CDCl3, 75 MHz):
162.0, 158.9, 153.9, 153.7, 133.3, 132.6, 132.2, 131.6,
119.7, 118.3, 116.9, 113.7, 83.5, 79.1, 69.8, 31.8, 29.5,
25.9, 22.8, 14.2. Anal. Calcd for C37H39NO3: C, 81.43; H,
7.20; N, 2.57; O, 8.80. Found: C, 81.30; H, 7.20; N, 2.55.
This compound has been reported previously and prepared
according to a previously reported procedure.45 Yield
91%; H NMR (CDCl3, 300 MHz): 7.42 (s, 4H), 3.16 (s,
1
1H), 1.13 (s, 21H); 13C NMR (CDCl3, 75 MHz): 132.1,
124.2, 122.1, 106.5, 93.2, 83.4, 79.0, 18.8, 11.5.
4.17. 4-(2,5-Bis-hexyloxy-4-{4-[(triisopropylsilanyl)-
ethynyl]-phenylethynyl}-phenyl)-but-3-yn-2-ol (18)
The general procedure for Sonogashira coupling was fol-
lowed using 2 and 17 (1.0 equiv) and a reaction time of
48 h at 75 ꢀC. The crude compound was purified by flash
column chromatography in ethyl acetate/hexanes (80:20)
to yield pure compound 18. Yield 96% (615 mg); IR (thin
1
film): 3410, 2933, 2863, 2152, 1505, 1216 cmꢁ1; H NMR
4.20. N-{4-[4-(4-{2,5-Bis-hexyloxy-4-[(triisopropylsi-
lanyl)-ethynyl]-phenylethynyl}-phenylethynyl)-2,5-bis-
hexyloxy-phenylethynyl]-phenyl}-formamide (21)
(CDCl3, 300 MHz): 7.39 (s, 4H), 6.89 (s, 1H), 6.83 (s,
1H), 3.90 (m, 4H), 1.74 (m, 4H), 1.57 (s, 6H), 1.45 (m,
4H), 1.28 (m, 8H), 1.08 (s, 21H), 0.84 (m, 6H); 13C NMR
(CDCl3, 75 MHz): 153.8, 153.7, 132.1, 131.5, 123.5,
123.5, 117.1, 116.9, 113.8, 113.8, 106.9, 99.6, 94.6, 92.9,
The general procedure for Sonogashira coupling was fol-
lowed using 20 and 11 (1.0 equiv) at 70 ꢀC. The crude

K. L. Chandra et al. / Tetrahedron 63 (2007) 7120–7132
7129
compound was purified by flash column chromatography
using ethyl acetate/hexanes (60:40) to yield pure 21. Yield
41% (150 mg); IR (thin film): 2928, 2863, 1594,
132.3, 131.7, 128.2, 126.6, 125.1, 124.9, 123.5, 123.3,
117.0, 116.9, 114.7, 114.2, 114.0, 113.3, 95.2, 94.9, 94.4,
93.3, 89.1, 88.2, 88.0, 87.9, 69.8, 69.7, 31.8, 30.5, 29.5,
29.4, 25.9, 25.9, 22.8, 14.2. Mass calculated for (M+)
C65H71NO5S 977.5053, found (HRMS-FAB) 977.5060.
1215 cmꢁ1
;
1H NMR (CDCl3, 300 MHz): 8.75 (d,
J¼11.4 Hz, 0.4H), 8.38 (d, J¼1.8 Hz, 0.5H), 7.53–7.49
(m, 8H), 7.06 (d, J¼8.9 Hz, 0.6H), 7.01 (s, 2H), 6.94 (s,
2H), 4.05–3.97 (m, 8H), 1.83 (m, 8H), 1.54 (m, 8H), 1.36
(m, 16H), 1.15 (s, 21H), 0.91 (m, 12H); 13C NMR (CDCl3,
75 MHz): 162.1, 159.2, 154.5, 153.9, 153.7, 153.6, 137.2,
136.7, 133.2, 132.6, 132.2, 131.6, 123.4, 120.5, 119.8,
118.4, 117.8, 116.9, 116.5, 114.4, 114.0, 113.9, 113.8,
123.4, 120.5, 119.8, 118.4, 117.8, 116.9, 116.5, 114.4,
114.0, 113.9, 113.8, 103.1, 96.9, 94.8, 94.6, 94.2, 88.3,
88.2, 86.0, 69.9, 69.8, 69.5, 31.9, 31.8, 31.8, 29.6, 29.5,
26.0, 25.9, 25.9, 22.8, 18.9, 14.3, 14.2, 11.5. Anal. Calcd
for C66H87NO5Si: C, 79.07; H, 8.75; N, 1.40; Si, 2.80; O,
7.98. Found: C, 78.82; H, 8.73; N, 1.48.
4.22. N-{4-[4-(4-{2,5-Bis-hexyloxy-4-[(triisopropylsi-
lanyl)-ethynyl]-phenylethynyl}-2,5-bis-hexyloxy-phe-
nylethynyl)-2,5-bis-hexyloxy-phenylethynyl]-phenyl}-
formamide (24)
The general procedure for Sonogashira coupling was fol-
lowed using 14 and 11 (1.0 equiv) at 75 ꢀC. The crude com-
pound was purified by flash column chromatography using
ethyl acetate/hexanes (60:40) to give pure 24. Yield 40%
(52 mg); mp 86 ꢀC; IR (thin film): 3286, 2933, 2857, 1690,
1424, 1212, 1023 cmꢁ1; 1H NMR (CDCl3, 300 MHz): 8.68
(d, J¼11.4 Hz, 0.33H), 8.31 (d, J¼0.9 Hz, 0.49H), 7.86 (d,
J¼11.4 Hz, 0.28H), 7.50–7.19 (m, 4H), 7.30–6.85 (m, 6H),
3.99–3.87 (m, 12H), 1.78 (m, 12H), 1.45 (m, 12H), 1.28
(m, 24H), 1.08 (s, 21H), 0.82 (m, 18H); 13C NMR (CDCl3,
75 MHz): 162.0, 159.0, 154.5, 153.8, 153.7, 153.4, 137.0,
133.2, 132.6, 119.7, 118.4, 118.1, 117.4, 117.2, 116.7, 114.5,
114.2, 114.1, 103.2, 96.7, 94.6, 91.8, 91.5, 86.2, 70.0, 69.8,
69.4, 31.9, 31.8, 29.6, 29.5, 26.0, 25.9, 25.8, 22.8, 18.9,
14.2, 11.6. Mass calculated for (M+) C78H111NO7Si
1201.8130, found (HRMS-FAB) 1201.8119.
4.21. Thioacetic acid S-[4-(4-{4-[2,5-bis-hexyloxy-4-(4-
isocyano-phenylethynyl)-phenylethynyl]-phenyl-
ethynyl}-2,5-bis-hexyloxy-phenylethynyl)-phenyl]
ester (23)
Compound 21 (150 mg) was taken and subjected to the gen-
eral procedure for fluoride-promoted deprotection. The crude
compound was purified by flash column chromatography us-
ing ethyl acetate/hexanes (60:40) to give pure compound,
which was used in the next step. Yield 90% (110 mg); IR
1
(thin film): 3286, 2928, 2863, 1690, 1410, 1215 cmꢁ1; H
4.23. Thioacetic acid S-[4-(4-{4-[2,5-bis-hexyloxy-4-(4-
isocyano-phenylethynyl)-phenylethynyl]-2,5-bis-hexyl-
oxy-phenylethynyl}-2,5-bis-hexyloxy-phenylethynyl)-
phenyl] ester (26)
NMR (CDCl3, 300 MHz): 8.75 (d, J¼11.4 Hz, 0.5H), 8.38
(d, J¼1.8 Hz, 0.7H), 7.88 (d, J¼11.4 Hz, 0.5H), 7.56–7.47
(m, 8H), 7.06 (d, J¼8.9 Hz, 0.6H), 6.99 (m, 4H), 4.03 (m,
8H), 3.35 (s, 1H), 1.84 (m, 8H), 1.54 (m, 8H), 1.35 (m, 16H),
0.89 (m, 12H); 13C NMR (CDCl3, 75 MHz): 162.1, 159.0,
154.3, 153.9, 153.8, 153.7, 137.1, 133.2, 132.6, 132.2, 131.6,
123.5, 123.3, 120.5, 119.7, 118.4, 117.9, 117.0, 114.5, 114.4,
114.1, 113.8, 113.0, 94.8, 87.9, 86.1, 82.6, 80.2, 69.8, 31.8,
31.7, 29.9, 29.5, 29.3, 25.9, 25.8, 22.8, 22.8, 14.2. The result-
ing intermediate was taken and subjected to the general pro-
cedure Sonogashira coupling with 4-iodo-phenyl thioacetate
(8) but at room temperature. The crude compound was puri-
fied by flash column chromatography using ethyl acetate/
Compound 24 was taken and deprotected using the general
procedure for fluoride-promoted deprotection. The com-
pound was purified by flash column chromatography using
ethyl acetate/hexanes (60:40) to give pure compound, which
1
was used in the next step. Yield 90% (45 mg); H NMR
(CDCl3, 300 MHz): 8.68 (d, J¼11.1 Hz, 0.3H), 8.32 (d,
J¼1.2 Hz, 0.5H), 7.84 (d, J¼11.1 Hz, 0.25H), 7.50–7.41
(m, 4H), 7.31 (s, 0.6H), 7.19 (s, 0.57H), 7.01–6.91 (m, 6H),
3.95 (m, 12H), 3.28 (s, 1H), 1.77 (m, 12H), 1.45 (m, 12H),
1.28 (m, 24H), 0.84–0.79 (m, 18H). This intermediate was
then taken and subjected to the general procedure for Sono-
gashira coupling using 4-iodo phenyl thioacetate (8) but at
room temperature. The crude compound was purified by
flash column chromatography using ethyl acetate/hexanes
(60:40) to give pure 25. Yield 66% (30 mg); 1H NMR
(CDCl3, 300 MHz): 8.68 (d, J¼11.7 Hz, 0.82H), 8.32 (d, J¼
1.2 Hz, 0.89H), 7.70 (d, J¼11.7 Hz, 0.25H), 7.50–7.42 (m,
4H), 7.33–7.24 (m, 4H), 7.19 (s, 0.57H), 6.95 (m, 6H),
3.95 (m, 12H), 2.38 (s, 3H), 1.79 (m, 12H), 1.45 (m 12H),
1.28 (m, 24H), 0.82 (m, 18H). The general procedure for
phosgene-mediated dehydration of formamide to isonitrile
was followed using molecule 25. The crude compound
was purified by flash column chromatography using ethyl
acetate/hexanes (20:80) to yield pure 26. Yield 58%
(17 mg); mp 120 ꢀC; IR (thin film): 2925, 2852, 2124,
1713, 1427, 1215 cmꢁ1; 1H NMR (CDCl3, 300 MHz): 7.47
(m, 4H), 7.35–7.28 (m, 4H), 6.95 (s, 3H), 6.94 (s, 3H), 3.96
(m, 12H), 2.37 (s, 3H), 1.79 (m, 12H), 1.47 (m, 12H), 1.29
(m, 24), 0.83 (m, 18H). Mass calculated for (M+)
C77H95NO7S 1178.6829, found (HRMS-FAB) 1178.6797.
1
hexanes (60:40) to yield pure 22. Yield 60% (78 mg); H
NMR (CDCl3, 300 MHz): 8.60 (d, J¼11.1 Hz, 0.4H), 8.21
(s, 0.5H), 7.93 (d, J¼11.4 Hz, 0.4H), 7.44–7.36 (m, 10H),
7.28–7.23 (m, 2H), 6.91 (d, J¼8.1 Hz, 0.5H), 6.86 (s, 4H),
3.88 (t, J¼6.6 Hz, 8H), 2.29 (s, 3H), 1.69 (m, 8H), 1.39 (m,
8H), 1.21 (m, 16H), 0.75 (m, 12H); 13C NMR (CDCl3,
75 MHz): 193.8, 162.1, 159.0, 153.9, 153.9, 153.8, 153.8,
137.0, 134.4, 133.2, 132.6, 132.3, 131.6, 128.2, 124.9, 123.4,
119.8, 119.7, 118.4, 117.0, 114.4, 114.2, 114.0, 95.0, 94.8,
94.3, 88.1, 87.9, 86.1, 69.8, 31.8, 31.8, 30.5, 29.5, 25.9,
25.9, 22.8, 14.2. The general procedure for phosgene-medi-
ated dehydration of formamide to isonitrile was followed us-
ing molecule 22. The crude compound was purified by flash
column chromatography using ethyl acetate/hexanes (20:80)
to yield pure 23. Yield 82% (62 mg); mp 118 ꢀC; IR (thin
film): 2929, 2852, 2360, 2119, 1709, 1512, 1215,
1
1018 cmꢁ1; H NMR (CDCl3, 300 MHz): 7.51–7.45 (m,
8H), 7.35–7.28 (m, 4H), 6.95 (s, 2H), 6.94 (s, 2H), 3.97 (t,
J¼6.3 Hz, 8H), 2.37 (s, 3H), 1.79 (m, 8H), 1.50 (m, 8H),
1.29 (m, 16H), 0.85 (m, 12H); 13C NMR (CDCl3,
75 MHz): 193.7, 165.9, 154.0, 153.9, 153.8, 134.4, 132.6,

7130
K. L. Chandra et al. / Tetrahedron 63 (2007) 7120–7132
4.24. 1,3,5-Tris-(4-ethynyl-phenylethynyl)-benzene (28)
sodium sulfate before drying in vacuum. The crude product
was purified by column chromatography using ethyl acetate/
hexanes (20:80) to yield 4.6 g (72%) of pure compound.
Spectral data matched that reported previously.47 Mp
Inside a N2-filled dry box, 1,3,5-tribromobenzene (157 mg,
0.5 mmol), 4-ethynyl-phenylethynyltriisopropyl silane
(425 mg, 1.5 mmol), tris(dibenzylideneacetone)bispalla-
dium (15.5 mg, 0.015 mmol), triphenylphosphine (13.1 mg,
0.05 mmol), and copper iodide (9.5 mg, 0.05 mmol) were
weighed in an oven dried Schlenk flask. Triethylamine
(5 mL) was added to the reaction mixture. The reaction mix-
ture was stirred for 48 h at 75 ꢀC. The reaction mixture was
cooled to room temperature and filtered through a small silica
gel plug and washed with dichloromethane. The filtrate was
evaporatedand the residuewas purified byflash column chro-
matography using ethyl acetate/hexanes (2:98) to yield
190 mg (41%) of 27. IR (thin film): 2942, 2864, 2154,
1
48 ꢀC; IR (thin film): 3333, 2981, 1581, 1163 cmꢁ1; H
NMR (CDCl3, 300 MHz): 7.52 (s, 1H), 7.40 (d, J¼2.1 Hz,
2H), 2.38 (br, 1H, –OH), 1.53 (s, 6H); 13C NMR (CDCl3,
75 MHz): 134.1, 133.2, 126.3, 122.7, 96.6, 79.5, 65.7, 31.5.
4.27. 4-{3,5-Bis-[(triisopropylsilanyl)-ethynyl]-phenyl}-
2-methyl-but-3-yn-2-ol (35)
Inside a N2-filled dry box, 34 (500 mg, 1.48 mmol), tris-
(dibenzylideneacetone)bispalladium (80 mg, 0.07 mmol),
triphenylphosphine (100 mg, 0.38 mmol), and copper iodide
(30 mg, 0.148 mmol) were weighed in an oven dried
Schlenk flask. Tetrahydrofuran (5 mL) and Hunig’s base
(20 mL) were added to the reaction mixture. The reaction
mixture was stirred for 5 min and then triisopropylsilyl acet-
ylene (840 mL, 3.71 mmol) was added. The reaction mixture
was stirred for 48 h at 60 ꢀC. The reaction mixture was
cooled to room temperature and filtered through a small sil-
ica gel plug and washed with dichloromethane. The filtrate
was evaporated and the residue was purified by flash column
chromatography using ethyl acetate/hexanes (20:80) to yield
658 mg (97%) of compound 35. Mp 40 ꢀC; IR (thin film):
3322, 2942, 2864, 2154, 1579, 1462, 1162 cmꢁ1; 1H NMR
(CDCl3, 300 MHz): 7.46 (m, 1H), 7.45 (m, 2H), 1.60 (s,
6H), 1.12 (s, 42H); 13C NMR (CDCl3, 75 MHz): 134.9,
134.8, 124.2, 123.3, 105.3, 95.0, 92.3, 80.8, 65.7, 31.5,
18.8, 11.4. Anal. Calcd for C33H52O2Si2: C, 76.08; H,
10.06; Si, 10.78; O, 3.07. Found: C, 76.32; H, 10.05.
1462 cmꢁ1 1H NMR (CDCl3, 300 MHz): 7.57 (s, 3H),
;
7.41 (s, 12H), 1.09 (s, 63H); 13C NMR (CDCl3, 75 MHz):
134.2, 133.3, 132.2, 131.7, 125.3, 124.1, 122.5, 122.2, 106.7,
93.4, 91.2, 89.0, 18.9, 11.5. This intermediate was then
subjected to the general procedure for fluoride-promoted
deprotection of trialkyl-silyl acetylenes was followed using
compound 27 but using 3.5 equiv of TBAF. The residue
was purified by column chromatography using ethyl ace-
tate/hexanes (2:98) to give 90 mg (97%) of pure compound
28. Spectral data matched those reported previously.46 1H
NMR (CDCl3, 300 MHz): 7.57 (s, 3H), 7.41 (s, 12H), 3.14
(s, 3H); 13C NMR (CDCl3, 75 MHz): 134.3, 133.3, 132.3,
131.8, 125.2, 123.1, 122.7, 122.2, 90.9, 89.1, 83.3, 79.5.
4.25. Thioacetic acid 4-(4-{3,5-bis-[4-(4-acetylsulfanyl-
phenylethynyl)-phenylethynyl]-phenylethynyl}-phenyl-
ethynyl)-phenyl ester (29)
The general procedure for Sonogashira coupling was fol-
lowed using molecule 28 and p-iodo-phenyl thioacetate
(3 equiv) at room temperature. The crude material was puri-
fied by column chromatography using ethyl acetate/hexanes
(10:90) to yield 130 mg (70%) of 29. Spectral data matched
those reported previously.32 Mp 174 ꢀC; IR (thin film): 1709,
4.28. 1-Ethynyl-3,5-bis-[(triisopropylsilanyl)-ethynyl]-
benzene (36)
This compound has been reported previously,37 but a differ-
ent approach was employed here for its synthesis. The
general procedure for base-promoted deprotection of
trialkyl-silyl acetylenes was followed using molecule 35.
The residue was purified by column chromatography using
ethyl acetate/hexanes (10:90) to yield 388 mg (90%) of
pure compound as a colorless liquid. Spectral data matched
those reported previously.37 IR (thin film): 3305, 2943, 2158,
1462 cmꢁ1; 1H NMR (CDCl3, 300 MHz): 7.46 (s, 3H), 3.02
(s, 1H), 1.06 (s, 42H); 13C NMR (CDCl3, 75 MHz): 135.3,
124.3, 122.3, 105.2, 92.5, 82.2, 78.4, 18.9, 11.5.
1
1553, 1108 cmꢁ1; H NMR (CDCl3, 300 MHz): 7.57–7.48
(m, 9H), 7.45 (s, 11H), 7.37–7.28 (m, 7H), 2.38 (s, 9H);
13C NMR (CDCl3, 75 MHz): 193.5, 134.4, 134.3, 132.4,
131.9, 128.6, 125.3, 124.3, 123.5, 122.7, 122.3, 91.2, 91.0,
90.8, 89.2, 30.5.
4.26. 4-(3,5-Dibromo-phenyl)-2-methyl-but-3-yn-2-ol
(34)
This compound was prepared using a modification of the
procedure reported previously.47 Inside a N2-filled dry box,
1,3,5-tribromobenzene (6 g, 19 mmol), tris-(dibenzyl-
ideneacetone)bispalladium (30 mg, 0.028 mmol), triphenyl-
phosphine (75 mg, 0.28 mmol), and copper iodide (54 mg,
0.28 mmol) were weighed in an oven dried Schlenk flask.
Triethylamine (30 mL) and pyridine (20 mL) were added
to the reaction mixture. The reaction mixture was stirred
for 5 min and then added 2-methyl-3-butyn-2-ol (1.9 mL,
19 mmol) to it. The reaction mixture was stirred overnight
at 100 ꢀC. The reaction mixture was cooled to room temper-
ature and filtered through a small silica gel plug and washed
with dichloromethane. The filtrate was evaporated and taken
in dichloromethane, washed with 5% HCl, water and brine,
respectively. The organic layer was dried over anhydrous
4.29. N-(4-{3,5-Bis-[(triisopropylsilanyl)-ethynyl]-
phenylethynyl}-phenyl)-formamide (37)
Inside a N2-filled dry box, 36 (320 mg, 0.665 mmol), tris-
(dibenzylideneacetone)bispalladium (20 mg, 0.02 mmol),
triphenylphosphine (35 mg, 0.13 mmol), copper iodide
(30 mg, 0.06 mmol), and p-iodo-phenyl formamide 5 were
weighed in an oven dried Schlenk flask. Triethylamine
(5 mL) was added to the reaction mixture. The reaction mix-
ture was stirred for 48 h at 70 ꢀC. The reaction mixture was
cooled to room temperature and filtered through a small sil-
ica gel plug and washed with dichloromethane. The filtrate
was evaporated and the residue was purified by flash column
chromatography using ethyl acetate/hexanes (60:40) to yield
330 mg (83%) of compound 37. Mp 184 ꢀC; IR (thin film):

K. L. Chandra et al. / Tetrahedron 63 (2007) 7120–7132
7131
2942, 2864, 2155, 1690, 1579, 1292 cmꢁ1
;
1H NMR
The Schlenk flask was evacuated and back filled with nitro-
gen (two times). To this was added dry dichloromethane and
cooled to 0 ꢀC, and added triethylamine. A solution of ben-
zyltriethyl ammonium chloride (4.2 mg, 0.018 mmol) in
2 mL of dry dichloromethane was added dropwise. The reac-
tion mixture was stirred for 7 h and allowed to warm gradu-
ally to room temperature. The reaction mixture was taken in
water and extracted with dichloromethane. The organic
layer was washed with water and brine, respectively. The
organic layer was dried over sodium sulfate before drying
it under vacuum. The crude compound was purified by flash
column chromatography using ethyl acetate/hexanes (20:80)
to yield 40 mg (38%) of pure compound. IR (thin film):
2942, 2864, 1690, 1292 cmꢁ1; 1H NMR (CDCl3, 300 MHz):
7.67 (m, 3H), 7.55 (m, 6H), 7.43–7.35 (m, 6H), 2.45 (s, 6H);
13C NMR (CDCl3, 75 MHz): 193.5, 166.1, 135.3, 134.8,
134.5, 132.9, 132.6, 132.4, 131.4, 131.3, 128.8, 126.7, 124.4,
124.1, 124.0, 123.6, 90.5, 90.2, 89.3, 89.1, 30.5. Mass calcu-
lated for (M+) C35H21NO2S2 552.1092, found (HRMS-FAB)
552.1068.
(CDCl3, 300 MHz): 8.70 (d, J¼11.4 Hz, 0.5H), 8.42 (d,
J¼1.8 Hz, 0.5H), 8.33 (s, 0.5H), 7.51–7.45 (m, 7H), 7.02
(d, J¼8.4 Hz, 0.1H), 1.07 (s, 42H); 13C NMR (CDCl3,
75 MHz): 162.4, 159.1, 136.3, 137.1, 134.8, 133.4, 132.8,
124.3, 124.3, 123.8, 123.7, 119.8, 119.2, 118.3, 105.4,
105.3, 92.4, 92.3, 90.2, 88.4, 87.9, 18.8, 11.4; Anal. Calcd
for C37H51NOSi2: C, 76.36; H, 8.83; Si, 9.65; N, 2.41; O,
2.75. Found: C, 76.19; H, 8.89; N, 2.39.
4.30. N-[4-(3,5-Diethynyl-phenylethynyl)-phenyl]-form-
amide (38)
Compound 37 (330 mg, 0.55 mmol) was taken in dry THF
(4 mL) under nitrogen atmosphere and added a 1.0 M solu-
tion of tetrabutyl ammonium fluoride (1.4 mL, 1.4 mmol).
The reaction mixture was stirred overnight and extracted
from ethyl acetate and washed with brine. The organic layer
was dried over sodium sulfate before drying under vacuum.
The crude compound was purified by flash column chroma-
tography using ethyl acetate/hexanes (60:40) to yield
140 mg (89%) of pure 38. Mp 158 ꢀC; IR (thin film):
3290, 2351, 1688, 1293 cmꢁ1; 1H NMR (CDCl3, 300 MHz):
8.76 (d, J¼11.1 Hz, 0.4H), 8.40 (d, J¼1.8 Hz, 0.6H), 8.25
(d, J¼10.8 Hz, 0.2H), 7.51 (m, 7H), 7.07 (d, J¼8.7 Hz,
0.8H), 3.12 (s, 1H), 3.11 (s, 1H); 13C NMR (CDCl3,
75 MHz): 162.1, 159.0, 135.2, 133.4, 132.8, 123.1, 119.8,
118.3, 82.0, 78.8, 78.7; FAB(M+): 269.08. Mass calculated
for (M+) C19H11NO 269.0841, found (HRMS-FAB)
269.0828.
4.33. 4-(3,5-Bis-{4-[(triisopropylsilanyl)-ethynyl]-phe-
nylethynyl}-phenyl)-2-methyl-but-3-yn-2-ol (41)
The general procedure for Sonogashira coupling was fol-
lowed using molecule 34 (0.5 mmol) and molecule 17
(1.0 mmol). The crude product was purified by flash column
chromatography using ethyl acetate/hexanes (20:80). Yield
90% (335 mg); mp 92 ꢀC; IR (thin film): 3333, 2942,
2864, 2153, 1582 cmꢁ1 1H NMR (CDCl3, 300 MHz):
;
7.56 (s, 1H), 7.47 (s, 2H), 7.39 (s, 8H), 1.93 (s, 1H, –OH),
1.56 (s, 6H), 1.07 (s, 42H); 13C NMR (CDCl3, 75 MHz):
134.4, 134.2, 132.2, 131.6, 123.9, 123.7, 122.7, 106.7,
95.2, 93.3, 90.4, 89.6, 80.7, 65.8, 31.6, 18.8, 11.5. Mass cal-
culated for (M+) C49H61OSi2 721.4261, found (HRMS-
FAB) 721.4286.
4.31. Thioacetic acid 4-[3-(4-acetylsulfanyl-phenyl-
ethynyl)-5-(4-formylaminophenyl ethynyl)-phenyl-
ethynyl]-phenyl ester (39)
Inside a N2-filled dry box, 38 (100 mg, 0.35 mmol), tris-
(dibenzylideneacetone)bispalladium (11 mg, 0.010 mmol),
triphenylphosphine (9 mg, 0.035 mmol), copper iodide
(6.6 mg, 0.035 mmol), and p-iodo-phenyl thioacetate 8
(194 mg, 0.7 mmol) were weighed in an oven dried Schlenk
flask. Tetrahydrofuran (1 mL) and triethylamine (2 mL)
were added to the reaction mixture. The reaction mixture
was stirred for 48 h at room temperature and filtered through
a small silica gel plug and washed with dichloromethane.
The filtrate was evaporated and the residue was purified by
flash column chromatography using ethyl acetate/hexanes
(60:40) to yield 106 mg (52%) of 39. Mp 62 ꢀC; IR (thin
4.34. 1-Ethynyl-3,5-bis-{4-[(triisopropylsilanyl)-ethyn-
yl]-phenylethynyl}-benzene (42)
The general procedure for base-promoted deprotection of tri-
alkyl-silyl acetylenes was followed using molecule 41. The
crude compound was purified by flash column chromato-
graphy using ethyl acetate/hexanes (10:90) to yield pure
42. Yield 68% (120 mg); IR (thin film): 3301, 2942, 2864,
2361, 2153, 1579 cmꢁ1; 1H NMR (CDCl3, 300 MHz): 7.61
(d, J¼1.5 Hz, 1H), 7.54 (t, J¼1.2 Hz, 2H), 7.41 (d, J¼
1.2 Hz, 8H), 3.06 (s, 1H), 1.08 (s, 42H); 13C NMR (CDCl3,
75 MHz): 134.8, 132.2, 131.6, 124.1, 124.1, 123.2, 122.7,
106.7, 93.3, 90.6, 89.5, 82.1, 78.7, 18.9, 11.5. Mass calcu-
lated for (M+) C46H54Si2 663.3842, found (HRMS-FAB)
663.3886.
film): 3317, 2194, 1699, 1519, 1117 cmꢁ1 1H NMR
;
(CDCl3, 300 MHz): 8.68 (d, J¼11.4 Hz, 0.3H), 8.27 (s,
0.5H), 8.18 (d, J¼10.8 Hz, 0.3H), 7.67–7.31 (m, 15H),
6.98 (d, J¼8.4 Hz, 0.8H), 2.38 (s, 6H); 13C NMR (CDCl3,
75 MHz): 193.9, 193.8, 162.1, 159.2, 137.5, 134.5, 134.2,
133.4, 132.8, 132.4, 128.7, 128.6, 124.3, 124.2, 124.1,
123.9, 123.8, 119.8, 118.9, 118.3, 90.0, 89.9, 89.6, 30.5.
Mass calculated for (M+) C35H23NO3S2 570.1198, found
(HRMS-FAB) 570.1206.
4.35. 4-[4-(3,5-Bis-{4-[(triisopropylsilanyl)-ethynyl]-
phenylethynyl}-phenylethynyl)-phenyl]-2-methyl-but-
3-yn-2-ol (43)
4.32. Thioacetic acid 4-[3-(4-acetylsulfanyl-phenyl-
ethynyl)-5-(4-isocyano-phenylethynyl)-phenylethynyl]-
phenyl ester (40)
The general procedure for Sonogashira coupling was fol-
lowed using molecule 42 and 4-(4-iodo-phenyl)-2-methyl-
but-3-yn-2-ol (1.0 equiv). The crude compound was purified
by column chromatography using ethyl acetate/hexanes
(25:75) to yield pure 43. Yield 65% (96 mg); mp 70 ꢀC; IR
Compound 39 (110 mg, 0.18 mmol) and triphosgene
(28 mg, 0.09) were weighed in an oven dried Schlenk flask.
(thin film): 2940, 2863, 2149, 1578 cmꢁ1 1H NMR
;

7132
K. L. Chandra et al. / Tetrahedron 63 (2007) 7120–7132
20. Pollack, S. K.; Naciri, J.; Mastrangelo, J.; Patterson, C. H.;
Torres, J.; Moore, M.; Shashidhar, R.; Kushmerick, J. G.
Langmuir 2004, 20, 1838–1842.
21. Zhao, Y.; Shirai, Y.; Slepkov, A. D.; Cheng, L.; Alemany, L. B.;
Sasaki, T.; Hegmann, F. A.; Tour, J. M. Chem.—Eur. J. 2005,
11, 3643–3658.
(CDCl3, 300 MHz): 7.58 (s, 3H), 7.39 (m, 12H), 2.09 (br s,
1H, –OH), 1.57 (s, 6H), 1.08 (s, 42H); 13C NMR (CDCl3,
75 MHz): 134.3, 132.2, 131.8, 131.7, 131.6, 124.1, 124.0,
123.2, 122.7, 106.7, 96.0, 93.3, 90.5, 89.6, 81.9, 65.8, 31.6,
18.8, 11.5. Anal. Calcd for C57H64OSi2: C, 83.36; H, 7.85;
Si, 6.84; O, 1.95. Found: C, 83.11; H, 7.76.
22. Shirai, Y.; Zhao, Y.; Cheng, L.; Tour, J. M. Org. Lett. 2004, 6,
2129–2132.
23. Meier, H.; Ickenroth, D.; Stalmach, U.; Koynov, K.; Bahtiar,
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Acknowledgements
€
€
24. Hoger, S.; Bonrad, K.; Mourran, A.; Beginn, U.; Moller, M.
We thank the National Science Foundation (DMR-0303746)
for the support of this work and Jennifer Ayres for a critical
reading of this manuscript. Mass spectra were obtained at the
Mass Spectrometry Laboratory for Biotechnology. Partial
funding for the Facility was obtained from the North
Carolina Biotechnology Center, North Carolina State Uni-
versity Department of Chemistry, and the National Science
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