Regioselective synthesis of tetraalkynylarenes by consecutive dual sonogashira coupling reactions of the bis(triflate) of 4,5-diiodobenzene-1,2- diol

Article abstract of DOI:10.1002/ejoc.201200079

The regioselective synthesis of nonsymmetric tetraalkynylarenes has been readily achieved through consecutive sets of Sonagashira cross-coupling reactions of the bis(triflate) derivative of 4,5-diiodobenzene-1,2-diol. The initial coupling reactions procee

Full text of DOI:10.1002/ejoc.201200079

FULL PAPER
DOI: 10.1002/ejoc.201200079
Regioselective Synthesis of Tetraalkynylarenes by Consecutive Dual Sonogashira
Coupling Reactions of the Bis(triflate) of 4,5-Diiodobenzene-1,2-diol
Thomas J. Fisher[a] and Patrick H. Dussault*[a]
Keywords: Cross-coupling / Regioselectivity / Palladium / Alkynes
The regioselective synthesis of nonsymmetric tetraalkynylar-
enes has been readily achieved through consecutive sets of
Sonagashira cross-coupling reactions of the bis(triflate) de-
rivative of 4,5-diiodobenzene-1,2-diol. The initial coupling
reactions proceeded with nearly complete selectivity for the
reaction at the Ar–I linkages. Subsequent coupling reactions
at the Ar–OTf linkages were efficiently conducted. The tetra-
alkynylarene products are of interest as components of or-
ganic molecular materials.
report the synthesis of the bis(triflate) ester of 4,5-diiodo-
benzene-1,2-diol and the application of this previously un-
reported electrophile in the regiocontrolled synthesis of tet-
raalkynylarenes (Scheme 1).
Introduction
The palladium-catalyzed cross-coupling reactions of aryl
halides or triflates with terminal alkynes is a popular
method for the synthesis of arylalkynes.[1] One class of reac-
tion products, tetraalkynylarenes, is of particular interest in
the field of organic materials.[2] Tetraalkynylbenzenes con-
taining four identical alkyne side-chains can be prepared
from nonselective coupling reactions of tetrahaloarenes.[3]
However, regio-defined synthesis of unsymmetrical tetra-
alkynylarenes also requires control of the sequence of cross-
coupling steps. A reported solution to this challenge ex-
ploits the greater reactivity of aryl iodides relative to aryl
bromides.[1,2] However, in some cases, the sequential cou-
pling reactions of iodo/bromoarenes have resulted in low
yields of tetraalkynylarenes, presumably reflecting the lower
reactivity and cross-coupling efficiency of aryl bromides
and/or the corresponding requirement for more forcing re-
action conditions.[4] Indeed, in the course of investigations
requiring the preparation of unsymmetrical tetraalkynes, we
found that attempted two-fold Sonagashira cross-coupling
of model 1,2-dibromoarenes failed to give bis(alkyne) prod-
ucts. As a result, we became interested in the possibility of
performing consecutive dual Sonogashira coupling reac-
tions with an arene bearing both ortho-diiodide and ortho-
bis(triflate) units.
Scheme 1. Synthetic approach to tetraalkynylarenes.
Results and Discussion
Diiodo bis(triflate) 1 was readily prepared in three steps
from 1,2-dimethoxybenzene as shown in Scheme 2. Electro-
philic iodination of 1,2-dimethoxybenzene proceeded in
86% yield.[7] Bis(demethylation), followed by disulfonyl-
ation of the resulting catechol proceeded quantitatively to
furnish 1. We used this procedure to prepare up to 20 g
of 1, which is stable in the dark at room temperature for
months.
The higher reactivity of aryl iodides relative to aryl tri-
flates as substrates for C–C cross-coupling reactions is well
established,[5] and we were encouraged by a few reports de-
scribing the successful use of arene-1,2-diyl bis(triflates) as
substrates for Sonogashira coupling reactions.[6] Herein, we
Scheme 2. Synthesis of 1.
[a] Department of Chemistry and Center for Nanohybrid
Functional Materials, University of Nebraska,
Lincoln, NE 68588, USA
The selectivity of Sonagashira coupling reactions of 1
was investigated by using the benzyl ether of 4-pentynol as
a model alkyne (Table 1). [PdCl2(PPh3)2] proved to be an
efficient catalyst at a loading of 6 mol-% (Entry 1). Good
Fax: +1-402-472-9402
E-mail: pdussault1@unl.edu
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201200079.
Eur. J. Org. Chem. 2012, 2831–2836
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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T. J. Fisher, P. H. Dussault
FULL PAPER
yields of the 1,2-bis(alkynyl) product could be obtained at actions were complete in 3 h, some alkynes required longer
lower catalyst loadings but at the cost of extended reaction times for the complete consumption of the starting material
times (Entry 4). Complete conversion of the starting mate- (Entries 2 and 14). The reactions proceeded smoothly with
rial at lower catalyst loadings could be achieved by per- alkynes functionalized with esters (Entry 2), nitriles (En-
forming the reaction at higher temperatures (Entry 5), but try 3), silyl ethers (Entry 4), alkyl chlorides (Entry 5), THP
these conditions resulted in the formation of copious ethers (Entry 10), and an acetal (Entry 12). Aromatic alk-
amounts of byproducts that were difficult to separate from ynes also proved to be excellent coupling partners (En-
the desired diyne. Alternative sources of PdII or Pd0 pro- tries 7–9). Coupling reactions with nonpolar alkynes (e.g.,
vided lower conversions and only trace amounts of the heptyne) appeared to proceed to completion (TLC); how-
product (Entries 8 and 9). A 2:1 ratio of CuI/PdII proved ever, because of the difficulty in completely separating the
optimal for the transformation. Complete selectivity for the products from recovered alkyne and nonpolar byproducts
coupling of the aryl iodides was found when 2.3 equiv. of by silica chromatography, these examples are not reported.
alkyne were used; no appreciable amounts of products re- Cross-coupling with a tertiary propargyl alcohol proceeded
sulting from coupling to the triflates were detected. How- in good yield (Entry 11), whereas reactions with unhindered
ever, performing the reaction in the presence of a large ex- propargyl ethers (Entries 13 and 14) provided lower yields
cess (5 equiv.) of alkyne did lead to the formation of signifi- of the bis(alkynes). Given the frequent application of pro-
cant amounts of inseparable byproducts, which appeared to pargyl alcohols and ethers as nucleophiles in Sonagashira
include the tri- and tetraalkynylbenzene (not shown).
coupling reactions,[1] we are uncertain as to why their use
has limitations in this setting.
Table 1. Optimization of the alkyne coupling reaction with 1.[a]
Table 2. Substrate scope for the selective coupling of 1.[a]
Entry
Pd cat. (amount
[mol-%])
Alkyne
equiv.
Conv.
[%]
Yield[b]
[%]
Entry
R
t [h]
Product, yield[b] [%]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
(CH2)3OBn
(CH2)3OBz
(CH2)3CN
(CH2)4OTBS
(CH2)4Cl
TIPS
3
5
3
3
3
3
3
3
3
3
3
3
3
5
2a, 84
2b, 71
2c, 78
2d, 94
2e, 76
2f, 46
2g, 78
2h, 69
2h, 84[c]
2i, 85
2j, 72
2k, 69
2l, 46
2m, 43
1
2
3
[PdCl2(PPh3)2] (6)
[PdCl2(PPh3)2] (3)
[PdCl2(PPh3)2] (1)
[PdCl2(PPh3)2] (3)
[PdCl2(PPh3)2] (3)
[PdCl2(PPh3)2] (6)
[PdCl2(PPh3)2] (6)
[Pd(PPh3)4] (6)
2.3
2.3
2.3
2.3
2.3
2.1
2.5
2.3
2.3
Ͼ99
68
67
Ͼ99
Ͼ99
Ͼ95
Ͼ99
52
84
16
2
70
nd
69
81
trace
trace
4[c]
5[d]
6
4-MeOC6H4
2-Py
7
8
9
2-Py
[PdCl2(dppf)] (6)
47
(CH2)2OTHP
C(CH3)2OH
CH(OEt)2
CH2OBz
[a] Reagents: 1 (0.4 mmol), CuI/Pd (2:1); nd = not determined. [b]
Isolated yield. [c] Time = 10 h. [d] T = 60 °C.
The selectivity of the reaction is significant. One might
envisage that the introduction of an alkyne in the first Son-
agashira coupling might direct the second coupling away
from the ortho iodide and towards one of the electron-de-
ficient, but sterically unencumbered triflate units; electron-
CH2OBn
[a] Reagents: 1 (0.4 mmol), THF (1 mL). [b] Isolated yield. [c] On
a 3.2 mmol scale.
We next investigated the conditions for displacing both
poor aryl halides are typically favored as electrophiles in triflates in a second set of Sonogashira coupling reactions
alkyne cross-coupling reactions.[8] However, the selective (Table 3). By using conditions related to those reported by
Sonogashira coupling of aryl iodides in the presence of aryl Powell and Rychnovsky,[6a] diyne 2a was coupled with the
triflates has previously been demonstrated.[5] Interestingly, TBS ether of 5-hexynol to yield tetrayne 3a in 72% yield
the reaction of 1 with only 1.1 equiv. of (4-methoxyphenyl)- (Entry 1). Further modification of the reported conditions
ethyne under typical reaction conditions generated the di- did not lead to any notable improvement (data not shown).
yne and monoyne in a 1.3:1 ratio in a combined yield of The scope of the second set of coupling reactions was then
81% (not shown). The modest preference for dialkynylation investigated (Entries 2–9).
could reflect a directing effect of the ortho-alkyne[9] or, al-
Finally, we compared our new approach directly against
ternatively, a more facile insertion into the hindered aryl an existing methodology for the synthesis of 3i, a target
iodide due to the diffusion-controlled proximity of the Pd previously prepared in four steps and 11% yield from 1,2-
catalyst to the electrophile.[10]
dibromo-4,5-diiodobenzene (Scheme 3).[2a] By using our
With the optimized reaction conditions in hand, we in- method, 3i could be prepared from diiododitriflate 1 in two
vestigated the scope of the selective cross-coupling reaction steps and 61% yield (or five steps and 53% overall yield
of 1 with a variety of alkynes (Table 2). Although most re- from 1,2-dimethoxybenzene).
2832
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Eur. J. Org. Chem. 2012, 2831–2836

Regioselective Synthesis of Tetraalkynylarenes
ring). NMR spectra were recorded in CDCl3 (by using residual
Table 3. Synthesis of tetraalkynylarenes by dual coupling of dialk-
ynylarenediyl bis(triflates).[a]
CHCl3: δ = 7.286 ppm) at 300/400/500/600 MHz (1H) or 75/100/
1
125/150 MHz (13C), as indicated. H NMR chemical shifts are re-
ported as δ in ppm as follows: chemical shift [multiplicity, coupling
constant(s) in Hz, integration]. 13C NMR chemical shifts are re-
ported as δ in ppm. IR spectra were recorded as neat ATR films
with selected absorbances reported in wavenumbers (cm–1).
1,2-Diiodo-4,5-dimethoxybenzene: This compound was prepared ac-
cording to the procedure of Lacour et al.[7] H5IO6 (0.41 equiv.,
25.6 mmol, 5.84 g) and MeOH (36 mL) were added to a flame-
dried 100 mL round-bottomed flask equipped with a short air con-
denser. The mixture was stirred at room temp., and then I2
(0.8 equiv., 50.2 mmol, 12.76 g) was added. The reaction mixture
was stirred vigorously for 10 min, after which 1,2-dimethoxyben-
zene (1 equiv., 63 mmol, 8.7 g, 8.0 mL) was added in one portion
through a syringe. The reaction mixture was heated at 70 °C in an
oil bath for 5 h, which resulted in the formation of a white solid
that made stirring difficult; however, the reaction proceeded even
without efficient stirring. The hot solution was poured into dilute
aqueous Na2S2O5 (ca. 100 mL), and the mixture was cooled to
room temp. The solid collected by filtration through a glass frit
was washed quickly with two 30 mL portions of cold MeOH and
dried in vacuo to afford 1,2-diiodo-4,5-dimethoxybenzene (21.07 g,
54 mmol, 86%) as a white solid that was deemed pure by NMR
spectroscopy and used without further purification. Rf = 0.49 (20%
ethyl acetate/hexane). M.p. 134.5–136.0 °C (ref.[7] 134 °C). 1H
NMR (600 MHz): δ = 7.25 (s, 2 H), 3.85 (s, 6 H) ppm. 13C NMR
(150 MHz): δ = 149.6, 121.7, 96.1, 56.2 ppm.
Entry
R
RЈ
Product, yield[b] [%]
1
2
3
4
(CH2)3OBn
(CH2)3OBn
(CH2)3OBn
(CH2)3OBn
(CH2)3OBn
(CH2)3OBn
(CH2)4OTBS
4-MeOC6H4
2-Py
(CH2)4OTBS
(CH2)3OBz
TMS
3a, 72
3b, 64
3c, 64
3d, 83
3e, 79
3f, 74
3g, 68
3h, 57
3i, 73
Ph
5
4-MeOC6H4
4-FC6H4
(CH2)3OBz
TMS
6
7[c]
8
9
4-(Bu2N)C6H4
[a] Reagents and conditions: on a 0.25 mmol scale, DMF/TEA
(5:1) (1.5 mL), sealed vial. [b] Isolated yield. [c] KI (3 equiv.) used
instead of TBAI.
1,2-Dihydroxy-4,5-diiodobenzene: A flame-dried 250 mL round-
bottomed flask was charged with 1,2-diiodo-4,5-dimethoxybenzene
(1 equiv., 10 mmol, 3.90 g) and then evacuated/back-filled with ni-
trogen (3ϫ) before addition of CH2Cl2 (70 mL). The solution was
cooled to 0 °C, and BBr3 (2.5 equiv., 25 mmol, 25 mL of a 1.0 m
solution in CH2Cl2) was added through a syringe pump over
20 min. The reaction mixture was stirred at 0 °C for 4 h and then
quenched with H2O (50 mL). The separated aqueous layer was ex-
tracted with Et2O (2ϫ75 mL). The combined organic layers were
dried with MgSO4, filtered through a pad of silica, and concen-
trated in vacuo to afford 1,2-dihydroxy-4,5-diiodobenzene (3.61 g,
9.99 mmol, quant.) as an off-white solid that was deemed pure by
NMR spectroscopy and used without further purification. Rf =
Scheme 3. Comparison of the protocol developed here with an exi-
sting methodology.
Conclusions
The selective Sonogashira cross-coupling reaction of 1,2-
diiodobenzene-4,5-diyl bis(triflate) proceeds with almost 0.50 (50% ethyl acetate/hexane). M.p. 116.0–116.5 °C. 1H NMR
(400 MHz, [D6]acetone): δ = 8.48 (br. s, 2 H), 7.38 (s, 2 H) ppm.
complete selectivity displacing both iodine atoms to furnish
a 4,5-bis(alkynyl)benzene-1,2-diyl bis(triflate), which can be
subjected to a second set of alkyne coupling reactions to
efficiently give nonsymmetric 1,2,4,5-tetraalkynylarenes.
Structurally related 1,2-diyl bis(triflates) have been shown
13C NMR (150 MHz, [D6]acetone): δ = 146.5, 125.6, 93.7 ppm.
4,5-Diiodo-1,2-phenylene Bis(trifluoromethanesulfonate) (1): 1,2-Di-
hydroxy-4,5-diiodobenzene (1 equiv., 7.85 mmol, 2.84 g), CH2Cl2
(55 mL), and pyridine (5 equiv., 39 mmol, 3.10 g, 3.16 mL) were
to undergo dual Suzuki coupling reactions,[6b] which sug- added to a flame-dried 100 mL round-bottomed flask. The solution
was cooled to 0 °C, and Tf2O (2.2 equiv., 17.3 mmol, 4.88 g,
2.91 mL) was added dropwise through a syringe over 10 min. The
reaction mixture was stirred for 6 h, while warming to ambient
temperature, then cooled to 0 °C, and quenched with H2O (30 mL).
The separated aqueous layer was extracted with CH2Cl2
(2ϫ30 mL). The combined organic layers were dried with MgSO4
and filtered through a tall pad of silica. The pad was washed care-
fully with CH2Cl2 to avoid the elution of impurities, and the filtrate
was concentrated in vacuo to afford 1 (4.90 g, 7.82 mmol, quant.)
as an off-white solid that was deemed pure by NMR spectroscopy
and used without further purification. (Note: For reactions in
which small amounts of impurities were observed after filtration,
the product could be obtained in pure form by column chromatog-
raphy utilizing 10% ethyl acetate/hexane as the mobile phase.) Rf
gests our results could potentially be extended to other
transition-metal-catalyzed cross-coupling reactions.
Experimental Section
General: All the reactions were carried out in flame-dried glassware
under dry nitrogen with magnetic stirring. Solvents were used as
purchased with the exception of THF and CH2Cl2, which were
distilled from Na/Ph2CO and CaH2, respectively. TLC was per-
formed on 0.25 mm hard-layer silica G plates; developed plates
were visualized with a UV lamp and/or by staining: vanillin (gene-
ral stain, after charring), 1% aq. KMnO4 (for unsaturated com-
pounds), I2, or phosphomolybdic acid (general stain, after char-
Eur. J. Org. Chem. 2012, 2831–2836
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2833

T. J. Fisher, P. H. Dussault
FULL PAPER
= 0.60 (10% ethyl acetate/hexane). M.p. 46.5–47.7 °C. 1H NMR
ethyl acetate/hexane, Rf = 0.27 (5% ethyl acetate/hexane). 1H NMR
(600 MHz): δ = 7.46 (s, 2 H), 3.63 (t, J = 6.6 Hz, 4 H), 2.57 (t, J
= 7.0 Hz, 4 H), 1.97–2.04 (4 H), 1.80–1.86 (4 H) ppm. 13C NMR
(150 MHz): δ = 138.9, 128.0, 126.5, 118.5 (q, JC,F = 320.7 Hz),
(400 MHz): δ = 7.91 (s, 2 H) ppm. 13C NMR (100 MHz): δ = 139.6,
133.4, 118.5 (q, JC,F = 321.0 Hz), 108.0 ppm. FTIR: ν = 1429,
˜
1335, 1215, 1125, 1105, 868, 788, 745, 689 cm–1. HRMS (ESI):
calcd. for C8H2F6I2NaO6S2 [M + Na]+ 648.7184; found 648.7164.
97.7, 77.7, 44.4, 31.6, 25.6, 19.0 ppm. FTIR: ν = 2946, 2230, 1489,
˜
1432, 1302, 1246, 1209, 1179, 1085, 862, 802, 597 cm–1. HRMS
(ESI): calcd. for C20H18F6O8S2Cl2Na [M + Na]+ 624.9724; found
624.9716.
General Procedure A. Sonogashira Coupling of 1: A flame-dried
8 mL vial fitted with a screw-top septum cap was charged with
[Pd(PPh3)2Cl2] (0.06 equiv., 0.024 mmol, 16.8 mg), CuI (0.12 equiv.,
0.048 mmol, 9.2 mg), and 1 (1 equiv., 0.40 mmol, 250 mg) and then
4,5-Bis[2-(triisopropylsilyl)ethynyl]-1,2-phenylene Bis(trifluoro-
evacuated/back-filled with nitrogen (3ϫ). A solution of the alkyne methanesulfonate) (2f): Yield: 136 mg, 0.184 mmol, 46 %. M.p.
(2.3 equiv., 0.92 mmol) in THF (1 mL) was then added, followed 42.3–43.5 °C. Mobile phase: 100% hexane. Rf = 0.43 (100% hex-
by Et3N (3 equiv., 1.2 mmol, 0.17 mL). The mixture was stirred at ane). 1H NMR (600 MHz): δ = 7.52 (s, 2 H), 1.14–1.21 (42 H)
room temp. for the required time (3–5 h) until the reaction was
complete (TLC) and then filtered through a plug of silica, which
was washed with Et2O. The combined eluents were concentrated in
vacuo and purified by flash chromatography (ethyl acetate/hexane)
to afford the diyne.
ppm. 13C NMR (150 MHz): δ = 139.3, 128.0, 127.3, 118.5 (q, JC,F
= 320.9 Hz), 102.1, 100.7, 18.7, 11.2 ppm. FTIR: ν = 2944, 2867,
˜
2363, 1485, 1436, 1385, 1211, 1167, 1135, 881, 834, 574 cm–1
.
HRMS (EI): calcd. for C30H44F6O6S2Si2Na [M]+ 734.2022; found
734.2020.
4,5-Bis(5-benzyloxypent-1-ynyl)-1,2-phenylene Bis(trifluoromethane-
sulfonate) (2a): Yield: 241 mg, 0.336 mmol, 84%. Mobile phase:
step gradient hexane to 10% ethyl acetate/hexane. Rf = 0.27 (10%
ethyl acetate/hexane). 1H NMR (600 MHz): δ = 7.42 (s, 2 H), 7.27–
7.39 (10 H), 4.56 (s, 4 H), 3.65 (t, J = 6.0 Hz, 4 H), 2.62 (t, J =
7.1 Hz, 4 H), 1.92–1.98 (m, 4 H) ppm. 13C NMR (150 MHz): δ =
4,5-Bis[2-(4-methoxyphenyl)ethynyl]-1,2-phenylene Bis(trifluoro-
methanesulfonate) (2g): Yield: 197 mg, 0.312 mmol, 78 %. M.p.
113.4–114.3 °C. Mobile phase: step gradient hexane to 7% ethyl
acetate/hexane. Rf = 0.30 (10% ethyl acetate/hexane). 1H NMR
(400 MHz): δ = 7.59 (s, 2 H), 7.51–7.57 (4 H), 6.90–6.97 (4 H), 3.88
(s, 6 H) ppm. 13C NMR (150 MHz): δ = 160.6, 139.0, 133.5, 127.8,
125.9, 118.5 (q, JC,F = 321.0 Hz), 114.3, 114.0, 97.7, 84.6,
138.8, 138.3, 128.4, 128.2, 127.59, 127.56, 126.3, 118.5 (q, JC,F
=
321.1 Hz), 98.1, 77.4, 73.0, 68.5, 28.6, 16.5 ppm. FTIR: ν = 2859,
55.4 ppm. FTIR: ν = 2205, 1605, 1513, 1485, 1435, 1414, 1290,
˜
˜
2230, 1489, 1433, 1210, 1178, 1135, 1080, 732 cm–1. HRMS (ESI):
calcd. for C32H28F6O8S2Na [M + Na]+ 741.1027; found 741.1039.
1248, 1213, 1130, 1027, 896, 828 cm–1. HRMS (ESI): calcd. for
C26H16F6O8S2Na [M + Na]+ 657.0088; found 657.0083.
5,5Ј-[4,5-Bis(trifluoromethylsulfonyloxy)-1,2-phenylene]dipent-4-
ynyl Dibenzoate (2b): Yield: 211 mg, 0.284 mmol, 71 %. Mobile
phase: step gradient hexane to 12% ethyl acetate/hexane. Rf = 0.20
(10% ethyl acetate/hexane). 1H NMR (400 MHz): δ = 8.01–8.11 (4
4,5-Bis[2-(pyridin-2-yl)ethynyl]-1,2-phenylene Bis(trifluoromethane-
sulfonate) (2h): Yield: 158 mg, 0.276 mmol, 69 %. M.p. 119.1–
120.2 °C. Mobile phase: 40% ethyl acetate/hexane. Rf = 0.30 (40%
ethyl acetate/hexane). 1H NMR (400 MHz): δ = 8.65–8.77 (2 H),
H), 7.53–7.60 (2 H), 7.39–7.48 (6 H), 4.51 (t, J = 6.3 Hz, 4 H), 2.71 7.67–7.83 (6 H), 7.31–7.40 (m, 2 H) ppm. 13C NMR (150 MHz): δ
(t, J = 7.0 Hz, 4 H), 2.12 (quint, J = 6.5 Hz, 4 H) ppm. 13C NMR
(150 MHz): δ = 166.5, 138.9, 133.0, 130.1, 129.6, 128.4, 128.0, JC,F = 320.8 Hz), 96.4, 84.2 ppm. FTIR: ν = 1581, 1561, 1493,
= 150.4, 142.2, 140.0, 136.3, 128.1, 127.3, 126.8, 123.8, 118.5 (q,
˜
126.5, 118.5 (q, JC,F = 321.4 Hz), 97.2, 77.8, 63.5, 27.6, 16.7 ppm.
1429, 1208, 1131, 1054, 1040, 904, 885, 833, 782, 732 cm–1. HRMS
FTIR: ν = 2210, 1716, 1489, 1433, 1271, 1246, 1209, 1177, 1134, (ESI): calcd. for C22H10F6N2O6S2Na [M + Na]+ 598.9782; found
˜
1085, 1070, 1027, 863, 808, 708 cm–1. HRMS (ESI): calcd. for 598.9783.
C32H24F6O10S2Na [M + Na]+ 769.0613; found 769.0609.
4,5-Bis[4-(tetrahydro-2H-pyran-2-yloxy)but-1-ynyl]-1,2-phenylene
4,5-Bis(5-cyanopent-1-ynyl)-1,2-phenylene Bis(trifluoromethane- Bis(trifluoromethanesulfonate) (2i): Yield: 230 mg, 0.340 mmol,
sulfonate) (2c): Yield: 173 mg, 0.312 mmol, 78 %. M.p. 56.8–
58.0 °C. Mobile phase: step gradient 25–35% ethyl acetate/hexane.
Rf = 0.35 (40% ethyl acetate/hexane). 1H NMR (600 MHz): δ =
7.49 (s, 2 H), 2.73 (t, J = 6.7 Hz, 4 H), 2.62 (t, J = 6.7 Hz, 4 H),
2.03 (quint, J = 6.7 Hz, 4 H) ppm. 13C NMR (150 MHz): δ = 139.2,
85%. Mobile phase: step gradient 10–20% ethyl acetate/hexane. Rf
= 0.22 (15% ethyl acetate/hexane). H NMR (600 MHz): δ = 7.45
(s, 2 H), 4.69–4.73 (2 H), 3.88–3.98 (4 H), 3.69 (dt, J = 9.7, 7.0 Hz,
2 H), 3.52–3.58 (2 H), 2.81 (t, J = 7.0 Hz, 4 H), 1.81–1.91 (2 H),
1.71–1.79 (2 H), 1.51–1.69 (8 H) ppm. 13C NMR (150 MHz): δ =
1
127.5, 126.7, 121.7, 118.5 (q, JC,F = 321.0 Hz), 95.4, 78.7, 24.2, 138.9, 128.0, 126.4, 118.5 (q, JC,F = 320.4 Hz), 98.9, 95.6, 77.8,
18.6, 16.2 ppm. FTIR: ν = 2231, 1490, 1431, 1401, 1246, 1223,
65.3, 62.2, 30.5, 25.4, 21.2, 19.4 ppm. FTIR: ν = 2944, 2873, 2234,
˜
˜
1212, 1131, 1084, 907, 858, 799, 749 cm–1. HRMS (ESI): calcd. for
C20H14F6N2O6S2Na [M + Na]+ 579.0095; found 579.0092.
1489, 1434, 1247, 1210, 1180, 1133, 1082, 976, 892, 859, 804,
733 cm–1. HRMS (ESI): calcd. for C22H28F6O10S2Na [M + Na]+
701.0926; found 701.0925.
4,5-Bis[6-(tert-butyldimethylsilyloxy)hex-1-ynyl]-1,2-phenylene
Bis(trifluoromethanesulfonate) (2d): Yield: 298 mg, 0.376 mmol,
4,5-Bis(3-hydroxy-3-methylbut-1-ynyl)-1,2-phenylene Bis(trifluoro-
94%. Mobile phase: step gradient hexane to 2% ethyl acetate/hex-
ane. Rf = 0.27 (2.5% ethyl acetate/hexane). H NMR (400 MHz): phase: step gradient 30–40% ethyl acetate/hexane. Rf = 0.22 (30%
methanesulfonate) (2j): Yield: 155 mg, 0.288 mmol, 72%. Mobile
1
1
δ = 7.44 (s, 2 H), 3.66–3.72 (4 H), 2.49–2.61 (4 H), 1.66–1.77 (8
ethyl acetate/hexane). H NMR (600 MHz): δ = 7.48 (s, 2 H), 3.65
H), 0.92 (s, 18 H), 0.08 (s, 12 H) ppm. 13C NMR (150 MHz): δ =
(br. s, 2 H), 1.66 (s, 12 H) ppm. 13C NMR (150 MHz): δ = 139.3,
138.8, 128.3, 126.3, 118.5 (q, JC,F = 320.9 Hz), 98.6, 77.3, 62.5, 127.5, 125.8, 118.5 (q, JC,F = 321.0 Hz), 102.2, 78.2, 65.6,
31.9, 25.9, 24.9, 19.4, 18.3, –5.3 ppm. FTIR: ν = 2945, 2930, 2858, 31.1 ppm. FTIR: ν = 3371, 2985, 1486, 1431, 1210, 1134, 1062,
˜
˜
2230, 1489, 1436, 11247, 1211, 1179, 1137, 1087, 834, 807, 952, 866, 826, 799, 734 cm– 1 . HRMS (ESI): calcd. for
774 cm–1. HRMS (ESI): calcd. for C32H48F6O8S2Na [M + Na]+
817.2131; found 817.2120.
C18H16F6O8S2Na [M + Na]+ 561.0088; found 561.0094.
4,5-Bis(3,3-diethoxyprop-1-ynyl)-1,2-phenylene Bis(trifluoro-
4,5-Bis(6-chlorohex-1-ynyl)-1,2-phenylene Bis(trifluoromethane- methanesulfonate) (2k): Yield: 172 mg, 0.276 mmol, 69%. Mobile
sulfonate) (2e): Yield: 185 mg, 0.304 mmol, 76%. Mobile phase: 4% phase: step gradient hexane to 5% ethyl acetate/hexane. Rf = 0.22
2834
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2012, 2831–2836

Regioselective Synthesis of Tetraalkynylarenes
(5% ethyl acetate/hexane). 1H NMR (600 MHz): δ = 7.58 (s, 2 H),
127.56, 125.3, 124.9, 95.0, 93.9, 79.6, 79.1, 73.0, 68.7, 63.7, 28.9,
5.52 (s, 2 H), 3.79–3.9 (4 H), 3.64–3.74 (4 H), 1.29 (t, J = 7.2 Hz, 28.0, 16.7, 16.6 ppm. FTIR: ν = 3675, 2988, 2972, 2901, 2229, 1716,
˜
12 H) ppm. 13C NMR (150 MHz): δ = 139.8, 127.0, 126.7, 118.5
1451, 1394, 1269, 1107, 1068, 1027, 900 cm–1. HRMS (ESI): calcd.
for C54H50O6Na [M + Na]+ 817.3505; found 817.3503.
(q, JC,F = 320.9 Hz), 92.51, 91.5, 80.3, 61.3, 15.1 ppm. FTIR: ν =
˜
3675, 2979, 2901, 1490, 1435, 1248, 1211, 1178, 1135, 1076, 1050,
868, 814 cm–1. HRMS (ESI): calcd. for C22H24F6O10S2Na [M +
Na]+ 649.0613; found 649.0610.
1,2-Bis(5-benzyloxypent-1-ynyl)-4,5-bis(2-trimethylsilylethynyl)benz-
ene (3c): Yield: 98 mg, 0.16 mmol, 64%. Mobile phase: 6% ethyl
acetate/hexane. Rf = 0.41 (10% ethyl acetate/hexane). 1H NMR
(600 MHz): δ = 7.48 (s, 2 H), 7.28–7.41 (10 H), 4.56 (s, 4 H), 3.66
(t, J = 6.1 Hz, 4 H), 2.61 (t, J = 7.0 Hz, 4 H), 1.94 (quint, J =
6.4 Hz, 4 H), 0.32 (s, 18 H) ppm. 13C NMR (150 MHz): δ = 138.5,
135.6, 128.4, 127.62, 127.61, 126.0, 124.5, 102.4, 100.0, 95.6, 79.0,
3,3Ј-[4,5-Bis(trifluoromethylsulfonyloxy)-1,2-phenylene]diprop-
2-ynyl Dibenzoate (2l): Yield: 127 mg, 0.184 mmol, 46 %. M.p.
78.4–79.5 °C. Mobile phase: step gradient hexane to 8 % ethyl
acetate/hexane. Rf = 0.35 (10% ethyl acetate/hexane). 1H NMR
(400 MHz): δ = 8.04–8.17 (4 H), 7.54–7.64 (4 H), 7.42–7.53 (4 H),
5.18 (s, 4 H) ppm. 13C NMR (150 MHz): δ = 165.7, 139.8, 133.5,
129.8, 129.3, 128.5, 127.1, 126.8, 118.5 (q, JC,F = 320.8 Hz), 91.6,
73.0, 68.7, 28.9, 16.6, 0.01 ppm. FTIR: ν = 2956, 2856, 2226, 2155,
˜
1481, 1454, 1249, 1103, 1077, 1028, 839, 758, 731, 696, 635 cm–1.
HRMS (ESI): calcd. for C40H46O2Si2Na [M + Na]+ 637.2934;
found 637.2922.
81.7, 52.7 ppm. FTIR: ν = 1724, 1490, 1434, 1265, 1246, 1210,
˜
1177, 1134, 1089, 1069, 869, 803, 709 cm–1. HRMS (ESI): calcd.
for C28H16F6O10S2Na [M + Na]+ 712.9987; found 712.9988.
1,2-Bis(5-benzyloxypent-1-ynyl)-4,5-bis(2-phenylethynyl)benzene
(3d): Yield: 130 mg, 0.208 mmol, 83%. Mobile phase: step gradient
5–10% ethyl acetate/hexane. Rf = 0.32 (10% ethyl acetate/hexane).
1H NMR (600 MHz): δ = 7.57–7.63 (6 H), 7.34–7.42 (14 H), 7.29–
7.34 (2 H), 4.58 (s, 4 H), 3.69 (t, J = 6.1 Hz, 4 H), 2.64 (t, J =
7.0 Hz, 4 H), 1.97 (quint, J = 6.6 Hz, 4 H) ppm. 13C NMR
(150 MHz): δ = 138.5, 135.1, 131.7, 128.7, 128.5, 128.4, 127.63,
127.61, 125.9, 124.6, 123.1, 95.6, 94.9, 87.6, 79.2, 73.0, 68.7, 28.9,
4,5-Bis(3-benzyloxyprop-1-ynyl)-1,2-phenylene Bis(trifluoro-
methanesulfonate) (2m): Yield: 114 mg, 0.172 mmol, 43%. Mobile
phase: step gradient hexane to 10% ethyl acetate/hexane. Rf = 0.27
(10% ethyl acetate/hexane). 1H NMR (600 MHz): δ = 7.55 (s, 2 H),
7.30–7.43 (10 H), 4.67 (s, 4 H), 4.43 (s, 4 H) ppm. 13C NMR
(150 MHz): δ = 139.6, 137.1, 128.5, 128.11, 128.07, 127.2, 126.8,
118.5 (q, JC,F = 320.4 Hz), 93.5, 82.2, 72.0, 57.6 ppm. FTIR: ν =
˜
16.6 ppm. FTIR: ν = 2856, 2224, 1597, 1497, 1364, 1102, 1076,
˜
3676, 2988, 2901, 1489, 1433, 1247, 1209, 1178, 1133, 1072, 864,
807, 737 cm–1. HRMS (ESI): calcd. for C28H20F6O8S2Na
[M + Na]+ 685.0402; found 685.0397.
1027, 899, 754, 734, 688 cm– 1 . HRMS (ESI): calcd. for
C46H38O6Na [M + Na]+ 645.2770; found 645.2759.
1,2-Bis(5-benzyloxypent-1-ynyl)-4,5-bis[2-(4-methoxyphenyl)-
ethynyl]benzene (3e): Yield: 135 mg, 0.198 mmol, 79 %. Mobile
phase: 15% ethyl acetate/hexane. Rf = 0.37 (20% ethyl acetate/hex-
General Procedure B. Sonogashira Coupling of Bis(triflates): A
flame-dried 8 mL vial fitted with a septum-containing screw-top
cap was charged with [Pd(PPh3)2Cl2] (0.06 equiv., 0.015 mmol,
10.6 mg), CuI (0.3 equiv., 0.075 mmol, 14.3 mg), and Bu4NI
(3 equiv., 0.75 mmol, 277 mg). The vessel was evacuated/back-filled
with nitrogen (3 ϫ), after which was added a solution of the
bis(triflate) (1 equiv., 0.25 mmol) in DMF/TEA (5:1, 1 mL). The
mixture was stirred at room temp. for 5 min, whereupon a solution
of alkyne (4 equiv., 1 mmol) in DMF/TEA (5:1, 0.5 mL) was
added. The capped vial was placed in an oil bath (70 °C) for 5.5 h
and then cooled to room temp. The reaction mixture was filtered
through a plug of silica, which was washed with Et2O. The com-
bined eluents were concentrated in vacuo and purified by flash
chromatography.
1
ane). H NMR (600 MHz): δ = 7.49–7.56 (6 H), 7.34–7.42 (8 H),
7.28–7.38 (2 H), 6.88–6.93 (4 H), 4.56 (s, 4 H), 3.86 (s, 6 H), 3.68
(t, J = 6.1 Hz, 4 H), 2.62 (t, J = 7.0 Hz, 4 H), 1.95 (quint, J =
6.6 Hz, 4 H) ppm. 13C NMR (150 MHz): δ = 159.2, 138.5, 134.8,
133.2, 128.4, 127.62, 127.59, 125.5, 124.7, 115.3, 114.1, 95.2, 94.9,
86.6, 79.3, 73, 68.7, 55.3, 28.9, 16.6 ppm. FTIR: ν = 2932, 2857,
˜
2209, 1604, 1568, 1511, 1289, 1246, 1172, 1141, 1104, 1027, 899,
829, 734, 696 cm–1. HRMS (ESI): calcd. for C48H42O4Na
[M + Na]+ 705.2981; found 705.2974.
1,2-Bis(5-benzyloxypent-1-ynyl)-4,5-bis[2-(4-fluorophenyl)ethynyl]-
benzene (3f): Yield: 122 mg, 0.185 mmol, 74%. Mobile phase: 8%
ethyl acetate/hexane. Rf = 0.36 (10 % ethyl acetate/hexane). 1H
NMR (600 MHz): δ = 7.52–7.58 (6 H), 7.34–7.42 (8 H), 7.28–7.34
(2 H), 7.05–7.11 (4 H), 4.57 (s, 4 H), 3.68 (t, J = 6.1 Hz, 4 H), 2.63
(t, J = 7.0 Hz, 4 H), 1.96 (quint, J = 6.6 Hz, 4 H) ppm. 13C NMR
(150 MHz): δ = 162.8 (d, JC,F = 250.5 Hz), 138.5, 135.0, 133.5 (d,
1,2-Bis(5-benzyloxypent-1-ynyl)-4,5-bis(6-tert-butyldimethylsilyl-
oxyhex-1-ynyl)benzene (3a): Yield: 151 mg, 0.18 mmol, 72%. Mo-
bile phase: 6% ethyl acetate/hexane. Rf = 0.54 (10% ethyl acetate/
1
hexane). H NMR (600 MHz): δ = 7.32–7.40 (10 H), 7.27–7.31 (2
H), 4.55 (s, 4 H), 3.69 (t, J = 5.9 Hz, 4 H), 3.65 (t, J = 6.2 Hz, 4
H), 2.59 (t, J = 7.0 Hz, 4 H), 2.51 (t, J = 6.6 Hz, 4 H), 1.93 (quint,
J = 6.7 Hz, 4 H), 1.67–1.78 (8 H), 0.93 (s, 18 H), 0.09 (s, 12 H)
ppm. 13C NMR (150 MHz): δ = 138.5, 135.2, 128.4, 127.60, 127.56,
125.2, 125.0, 95.4, 94.7, 79.2, 79.1, 73.0, 68.8, 62.7, 32.0, 28.9, 26.0,
JC,F = 8.6 Hz), 128.4, 127.61, 127.60, 126.0, 124.3, 119.2 (d, JC,F
=
4.4 Hz), 115.8 (d, JC,F = 22.5 Hz), 95.7, 93.7, 87.3, 79.1, 73.0, 68.7,
28.9, 16.6 ppm. FTIR: ν = 2926, 2856, 2225, 1600, 1567, 1507,
˜
1227, 1155, 1102, 899, 833, 792, 734, 696 cm–1. HRMS (ESI): calcd.
for C46H36F2O2Na [M + Na]+ 681.2581; found 681.2567.
25.1, 19.5, 18.4, 16.6, –5.3 ppm. FTIR: ν = 2928, 2855, 2209, 1487,
˜
1253, 1102, 900, 834, 774, 733, 696 cm–1. HRMS (ESI): calcd. for
C54H74O4Si2Na [M + Na]+ 865.5023; found 865.5006.
5,5Ј-{4,5-Bis[6-(tert-butyldimethylsilyloxy)hex-1-ynyl]-1,2-phen-
ylene}dipent-4-ynyl Dibenzoate (3g): Yield: 149 mg, 0.170 mmol,
5,5Ј-[4,5-Bis(5-benzyloxypent-1-ynyl)-1,2-phenylene]dipent-4-ynyl 68%. Mobile phase: 6% ethyl acetate/hexane. Rf = 0.36 (10% ethyl
1
Dibenzoate (3b): Yield: 127 mg, 0.16 mmol, 64%. Mobile phase:
15% ethyl acetate/hexane. Rf = 0.39 (20% ethyl acetate/hexane). 1H
NMR (600 MHz): δ = 8.04–8.10 (4 H), 7.54–7.60 (2 H), 7.42–7.47
(4 H), 7.39–7.41 (2 H), 7.33–7.38 (8 H), 7.27–7.31 (2 H), 4.55 (s, 4
H), 4.53 (t, J = 6.3 Hz, 4 H), 3.66 (t, J = 6.2 Hz, 4 H), 2.70 (t, J =
acetate/hexane). H NMR (600 MHz): δ = 8.03–8.08 (4 H), 7.34–
7.42 (8 H), 7.52–7.59 (2 H), 7.38–7.47 (6 H), 4.50 (t, J = 6.3 Hz, 4
H), 3.68 (t, J = 6.0 Hz, 4 H), 2.67 (t, J = 6.8 Hz, 4 H), 2.50 (t, J =
6.5 Hz, 4 H), 2.09 (quint, J = 6.5 Hz, 4 H), 1.65–1.77 (8 H), 0.92
(s, 18 H), 0.07 (s, 12 H) ppm. 13C NMR (150 MHz): δ = 166.5,
7.0 Hz, 4 H), 2.60 (t, J = 7.0 Hz, 4 H), 2.11 (quint, J = 6.6 Hz, 4 135.2, 132.9, 130.2, 129.6, 128.3, 125.4, 124.8, 95.6, 93.8, 79.6, 79.0,
H), 1.94 (quint, J = 6.6 Hz, 4 H) ppm. 13C NMR (150 MHz): δ =
166.5, 138.5, 135.3, 133.0, 130.2, 129.6, 128.38, 128.36, 127.60,
63.7, 62.6, 31.9, 28.0, 26.0, 25.1, 19.5, 18.3, 16.6, –5.3 ppm. FTIR:
˜
ν = 2951, 2928, 2856, 2231, 1719, 1270, 1107, 1070, 834, 709 cm–1.
Eur. J. Org. Chem. 2012, 2831–2836
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2835

T. J. Fisher, P. H. Dussault
FULL PAPER
HRMS (ESI): calcd. for C54H70O6Si2Na [M + Na]+ 893.4609;
found 893.4631.
Haley, J. Am. Chem. Soc. 2005, 127, 2464, and references
therein; c) K. Ohta, S. Yamada, K. Kamada, A. D. Slepkov,
F. A. Hegmann, R. R. Tykwinski, L. D. Shirtcliff, M. M.
Haley, P. Sałek, F. GelЈmukhanov, H. Ågren, J. Phys. Chem. A
2011, 115, 105.
1,2-Bis[2-(4-methoxyphenyl)ethynyl]-4,5-bis(2-trimethylsilylethynyl)-
benzene (3h): Yield: 76 mg, 0.143 mmol, 57%. Mobile phase: 4%
ethyl acetate/hexane. Rf = 0.38 (10 % ethyl acetate/hexane). 1H
NMR (600 MHz): δ = 7.66 (s, 2 H), 7.47–7.55 (4 H), 6.86–6.93 (4
H), 3.85 (s, 6 H), 0.31 (s, 18 H) ppm. 13C NMR (150 MHz): δ =
160.0, 135.2, 133.2, 125.6, 124.8, 115.1, 114.1, 102.4, 100.4, 95.7,
[3] a) W. Tao, S. Nesbitt, R. F. Heck, J. Org. Chem. 1990, 55, 63;
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86.4, 55.3, 0.0 ppm. FTIR: ν = 2959, 2213, 2156, 1605, 1513, 1290,
˜
1246, 1167, 1031, 828 cm–1. HRMS (EI): calcd. for C34H34O2Si2
[M]+ 530.2097; found 530.2093.
1,2-Bis{2-[4-(dibutylamino)phenyl]ethynyl}-4,5-bis[2-(2-pyridyl)-
ethynyl]benzene (3i): Yield: 134 mg, 0.183 mmol, 73%. Mobile
phase: 35% ethyl acetate/hexane. Rf = 0.35 (40% ethyl acetate/hex-
ane). 1H NMR (600 MHz): δ = 8.64–8.70 (2 H), 7.78 (s, 2 H), 7.73
(d, J = 7.6 Hz, 2 H), 7.67 (td, J = 7.8, 1.9 Hz, 2 H), 7.45 (d, J =
8.7 Hz, 2 H), 7.23–7.28 (2 H), 6.61 (d, J = 8.7 Hz, 4 H), 3.32 (t, J
= 7.9 Hz, 8 H), 1.61 (quint, J = 7.8 Hz, 8 H), 1.39 (sext, J = 7.6 Hz,
8 H), 0.99 (t, J = 7.3 Hz, 12 H) ppm. 13C NMR (150 MHz): δ =
150.1, 148.3, 143.5, 136.1, 134.8, 133.3, 127.8, 126.7, 123.4, 122.9,
111.2, 108.5, 98.0, 93.9, 87.4, 86.0, 50.7, 29.4, 20.3, 14.0 ppm.
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Supporting Information (see footnote on the first page of this arti-
1
cle): H and 13C NMR spectra for all compounds.
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Acknowledgments
We are grateful for financial support from the National Science
Foundation (NSF) (EPS 10040 94). Preliminary experiments were
conducted by Mitch Trauernicht.
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[1] R. Chinchilla, C. Najera, Chem. Rev. 2007, 107, 874; R. Chin-
chilla, C. Najera, Chem. Soc. Rev. 2011, 40, 5084.
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Received: January 23, 2012
Published Online: March 27, 2012
2836
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2012, 2831–2836