Routes to sydnone-containing oligomeric areneynes

Article abstract of DOI:10.1081/SCC-200050343

Iterative Sonogashira-coupling routes have been used to prepare sydnone-containing areneynes 1-3 (and related compounds) from ?-iodophenylsydnone (4). The best results were obtained by using two- and three-reaction-in-one-pot protocols.

Full text of DOI:10.1081/SCC-200050343

Synthetic Communicationsw, 35: 639–651, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200050343
Routes to Sydnone-Containing
Oligomeric Areneynes
Andrew J. Weisner
Chemistry Department, Wright State University, Dayton, Ohio, USA
Thomas M. Cooper
Materials and Manufacturing Directorate, Air Force Research
Laboratory, Wright Patterson Air Force Base, Ohio, USA
Kenneth Turnbull
Chemistry Department, Wright State University, Dayton, Ohio, USA
Abstract: Iterative Sonogashira-coupling routes have been used to prepare sydnone-
containing areneynes 1–3 (and related compounds) from o-iodophenylsydnone (4).
The best results were obtained by using two- and three-reaction-in-one-pot protocols.
Keywords: Alkynes, sydnones, Sonogashira coupling
INTRODUCTION
For a study exploring the preparation of sydnone-containing platinum
acetylides as potential non-linear optical materials, we required the
appropriate alkynyl sydnone ligands 1–3. The most feasible avenue to such
Received in the USA 12 November 2004
Address correspondence to Kenneth Turnbull, Chemistry Department, Wright State
University, Dayton, Ohio 45435, USA. E-mail: kenneth.turnbull@wright.edu

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A. J. Weisner, T. M. Cooper, and K. Turnbull
species appeared to be via iterative Sonogashira coupling protocols from 3-(2-
iodophenyl)sydnone 4. While the latter could be prepared successfully from
o-iodo-aniline,[1] in our hands, the overall yield of 4 was low (typically
15%–20%) and its purity was poor without multiple recrystallizations.
Accordingly, since 4 was to be a pivotal molecule for the remaining
syntheses, we endeavored to develop a more efficient preparation. Ultimately,
our successful approach lay in a “one-pot” combination of two previous,
separate findings from our laboratory, viz., that 3-phenylsydnone 5 (readily
available in two high-yield steps from commercially available N-
phenylglycine)[2] could be diiodinated (to form 7) via a dilithio intermediate
6,[3] and removal of an iodine from the sydnone C-4 position in 7 could be
effected using sodium sulfite.[4] Thus, treatment of 5 with three equivalents
of n-butyllithium at 2408C, followed by addition of excess iodine and work-
up with aqueous sodium sulfite, gave the monoiodo sydnone 4. The yield of
homogeneous material, suitable for further transformation, was as high as
80% without chromatography. Further, we were able to conduct the lithia-
tion/iodination process at a concentration approximately four-fold higher
than that we had reported previously,[3] rendering it a facile process for the
preparation of 4 on a 5–10 g scale.
With a satisfactory avenue to 4 in hand, the stage was set for exploration
of subsequent Sonogashira coupling protocols (to, e.g., 8–11), especially
using trimethylsilylacetylene as a precursor to the terminal sydnone alkyne
1. Successful Sonogashira coupling reactions were reported previously in
the sydnone arena, all at the 4-position of the sydnone ring,[5] and, accord-
ingly, there was no reason to expect an inherent instability of the sydnone
ring to such conditions. We elected to use a modification of Krause’s
protocol[6] and, indeed, heating at 508C of a degassed THF solution of 3-(2-
iodophenyl)sydnone (4) and a terminal alkyne in the presence of triethyl-
amine, (Ph3P)2PdCl2 and CuI, gave 66%–86% yields of the corresponding
sydnone acetylenes 8–11 (Scheme 1). The identities of the latter were
apparent from their satisfactory elemental analyses, infrared (IR) and
nuclear magnetic resonance (NMR) spectra. Thus, in their IR spectra, the
most definitive peaks were the sydnone C–H stretch at ꢀ3150 cm21, the
C;C stretch at ꢀ2200 cm21 and the sydnone C55O stretch at ꢀ1740 cm21
and, in the 13C-NMR spectra, the most definitive peaks were those for the
.
1
The H-NMR spectra for 8–11 showed the sydnone ring proton at ꢀ6.9 d

Routes to Sydnone-Containing Oligomeric Areneynes
641
sydnone C–4 position, at ꢀ97 ppm, the sydnone C–5 position, at ꢀ169 ppm,
and the two alkynyl carbons at ꢀ98 and ꢀ82 ppm7.
Conversion of the tetramethylsilane (TMS) acetylene coupled product 11
to the terminal alkyne 1 could be effected in 71% yield using potassium
carbonate, or in 63% yield using tetrabutylammonium fluoride. The identity
of the latter was apparent from the characteristic signals for a terminal
alkyne (viz., alkyne CH stretch at 3242 cm21 in the IR spectrum, and a
1
singlet at 3.43 d in the H-NMR spectrum). With 1 in hand, it was elected
to test whether or not it would undergo Sonogashira coupling with an aryl
iodide. Accordingly, using the same Sonogashira coupling conditions as
mentioned previously, 1 was allowed to react with iodobenzene; 8 was
obtained in 76% yield after only 2 hours. It was found later that the conversion
to 8 occurred readily even at room temperature. While this model study had
established that the three-step protocol (4 to 11 to 1 to 8) could be used as a
preparative route to o-alkynylsydnones, there were some obvious
drawbacks. First, as mentioned earlier, in principle, one could excise two
steps by reaction of 4 directly with an appropriate terminal alkyne (to form
e.g., 8). However, the number of commercially available, reasonably priced
terminal alkynes is more limited than are the available aryl iodides and, if
recourse to synthesis of the terminal alkyne is necessitated, the three-step
protocol still may be the more efficient route. Second, a three-step avenue
to 8 (and congeners) involves purification at each juncture, with obvious
losses of yield. Accordingly, it was decided to attempt the second two steps
[11 to 1 to 8 (and congeners)] in one pot, using tetrabutylammonium
fluoride (TBAF) for desilylation of the TMS acetylenic sydnone 11 (to form
1 in situ). Thus, treatment of 11 with TBAF (1M in tetrahydrofuran) at
room temperature effected conversion to the terminal acetylene (thin layer
chromatography (TLC) evidence) within 15 minutes. Subsequent addition of
Scheme 1. i) K2CO3, MeOH, H2O, or Bu4NF; ii) trimethylsilylacetylene, Cul, NEt3,
(Ph3P)2PdCl2, 508C, 16 h; iii) Bu4NF.

642
A. J. Weisner, T. M. Cooper, and K. Turnbull
the appropriate aryl iodide under Sonogashira coupling conditions gave the
corresponding internal alkynes 8, 12–16 in 27%–72% yield in 1–4 hours
at room temperature. The identity of compound 8 was confirmed by compari-
son with a previously prepared sample, while the remaining sydnone alkynes,
viz., 12–16, were characterized as discussed earlier for 8–11.
The preparation of the para-bromophenylalkynyl sydnone 16 allowed the
pursuit of further coupling protocols en route to the bis- and tris-alkynes 2 and
3, respectively. Accordingly, treatment of 16 with trimethylsilylacetylene at
508C overnight, under typical Sonogashira coupling conditions, afforded the
silylated bis acetylene 17 in 84% yield (homogeneous, not recrystalized).
Removal of the TMS group with tetrabutylammonium fluoride gave the
desired terminal acetylene 2, albeit in low yield (38%), and subsequent
reaction with 1-bromo-4-iodobenzene under Sonogashira conditions afforded
the para-bromophenyl bis acetylene 18 in 42% yield. Further Sonogashira
coupling of 18 with trimethylsilylacetylene (508C, overnight, to give 19)
followed by treatment with potassium carbonate (room temperature, over-
night), afforded 3 in 81% yield (homogeneous, not recrystalized) (Scheme 2).
At this stage, the desired terminal acetylenes 2 and 3 were available using
these iterative Sonogashira coupling protocols; however, the cumulative
yields from doing so were unacceptably low. Accordingly, attention was
given to the possibility of utilizing multistep, one-pot processes [as
developed for 11 to 8 (and congeners)] for the precursors to these species.
The first such attempt (three reactions in one-pot) was made for the conversion
of 3-(2-iodophenyl)sydnone (4) to the key intermediate 16. Thus, Sonogashira
coupling of 4 with trimethylsilylacetylene (508C, overnight), treatment with
tetrabutylammonium fluoride (room temperature, 10 minutes) and subsequent
addition of 1-bromo-4-iodobenzene (room temperature, 4 hours) gave the
desired 3-(2-(4-bromophenylethynyl)phenylsydnone (16) in 76% yield
overall. A subsequent 2-in-1 process was utilized for conversion of 16 to 2
in 86% yield, a 3-in-1 protocol led to the next level key intermediate 18 in
51% yield (from 16), and a 2-in-1 procedure was employed for the preparation
of 3 (81% from 18).
Scheme 2. i) trimethylsilylacetylene, Cul, NEt3, (Ph3P)2PdCl2, 508C, 12h; ii) K2CO3,
rt, 12 h.

Routes to Sydnone-Containing Oligomeric Areneynes
643
It is instructive to examine the effect of these multistep syntheses upon the
overall yields of the terminal alkynes 1, 2, and 3. Thus, from N-phenylsydnone
(5), 3-(2-ethynylphenyl)sydnone (1) required four reactions (in three steps)
with an overall yield of 16% for analytically pure material, 3-(2-(4-(ethynyl)
phenylethynyl)phenyl)sydnone (2) required seven reactions (in three steps)
with an overall yield of 21% for analytically pure material, and
3-(2-(4-(4-ethynyl)phenylethynyl)phenylethynyl)phenyl)sydnone (3) required
10 reactions (in four steps) for an overall yield of 11% for analytically pure
material. These satisfactory overall yields can be attributed to the power of
the multireaction in one-pot protocols. It should be noted, however, that in
practice, the yields of the final products are higher than were reported
earlier since it proved possible to utilize homogeneous, but unrecrystalized
material for subsequent reaction steps. Further, all of the terminal acetylenes
(1–3) recrystalized poorly, cutting down sharply on the overall yields. For
many purposes, the quality of the products obtained by column chromato-
graphy would suffice. Accordingly, if the overall yields are calculated based
on material obtained directly from column chromatography (homogenous
by TLC), using the most direct, multireaction in one-pot protocols, the
yields improve markedly. Thus, 3-(2-ethynyl-phenyl)sydnone (1) is prepared
from N-phenylsydnone (5) in 33% yield, 3-(2-(4-(ethynyl)-phenylethynyl)
phenyl)sydnone (2) is afforded in 21% yield, and 3-(2-(4-(4-ethynyl)-
phenyl-ethynyl)phenylethynyl)phenyl)sydnone (3) results in 25% yield.
Accordingly, the power of this approach is manifest.
Overall, we have developed relatively concise avenues to the desired
alkynylsydnones 1–3. The conversion of these alkynyl species to platinum
acetylides, and the nonlinear optical properties of the latter, will be
published in due course.
EXPERIMENTAL
General Notes
All starting reagents and catalysts were purchased from commercial sources
and used without further purification. Dry tetrahydrofuran (THF) was
distilled from sodium metal/benzophenone ketyl. All glassware was flame-
dried under an atmosphere of nitrogen prior to the use of dry reagents.
Melting points were determined on a Mel-Temp melting point apparatus
and are uncorrected. Infrared spectra were acquired on a Mattson Genesis II
FTIR. NMR spectra were acquired on either a Jeol or Inova 300 MHz NMR.
All Sonogashira reaction solutions were degassed in the following way
prior to the addition of the palladium catalyst: The reaction solution was
frozen in liquid nitrogen, purged with nitrogen 25 times, and allowed to thaw.
This freezing, purging, and thawing process then was repeated twice more.

644
A. J. Weisner, T. M. Cooper, and K. Turnbull
3-(2-Iodophenyl)sydnone (4)
To a stirred solution of 3-phenylsydnone (5) (3.00 g, 18.5 mmol) in dry THF
(300 mL), under an atmosphere of nitrogen at 2408C, n-butyl lithium
(1.4 M cyclohexane, 39.6 mL, 55.5 mmol) was added. After 30 min, excess
iodine (14.550 g, 57.4 mmol) was added and, after 1 h more, the reaction
was quenched at low temperature with aqueous Na2SO3 [20.00 g, 0.16 mol
in H2O (600 mL)]. The solution was allowed to reduce in volume overnight
with gentle stirring and the title compound was isolated as an orange solid
(4.27 g, 80%) by vacuum-filtration, washing with distilled water (50 mL),
and drying on the funnel overnight. Recrystallization from dichloro-
methane/hexanes afforded the title compound as light-orange needles
(2.6 g, 50%), m.p. 81–828C, identical (IR, m.p.) to an authentic sample.[2]
General Procedure for the Coupling of 3-(2-Iodophenyl)sydnone (4)
with Alkynes
3-(2-Iodophenyl)sydnone (4), the appropriate alkyne (ꢀ1.5 eq.) and triethyl-
amine (5 eq.) were dissolved in dry THF and the solution was deoxygenated.
Bistriphenylphosphinepalladium dichloride (5 mol%) was added and the
reaction was stirred for 10 min, followed by the addition of copper (I)
iodide (10 mol%). After heating at 508C for 4–15 h under an atmosphere of
dry nitrogen, the reaction was allowed to cool and the solvents were
removed in vacuo. Column chromatography (silica gel, 10% dichloro-
methane/hexanes to 100% dichloromethane) of the resulting black
semisolid gave a gold-colored semi-solid which, upon recrystalization from
dichloromethane/hexanes provided the desired compounds 8–11 as
colorless to pale yellow crystals.
3-(2-(Phenylethynyl)phenyl)sydnone (8)
Using 4(3.20 g, 11 mmol), phenyl acetylene (1.70 g, 17 mmol), and THF (160 mL)
in the general procedure gave, after 4 h, the title compound as colorless plates
(2.31 g, 80%), m.p. 74–758C. (Found: C, 73.12; H, 4.00; N, 10.66. Calc. for
C16H10N2O2: C, 73.27; H, 3.84; N, 10.68); nmax (KBr): 3130, 3075, 2224, 1750,
1
1502, 1435, 939, 761, 687 cm21; H NMR (CDCl3): d 7.8–7.3 (m, 9H), 6.9
(s, 1H); 13C NMR (CDCl3): 169.0 (C55O), 135.1, 134.0, 132.0, 131.8, 129.7,
129.5, 128.7, 124.9, 121.3, 119.1, 97.6 (sydnone C-4), 97.2, 82.3 ppm.
3-(2-(4-Methylphenylethynyl)phenyl)sydnone (9)
Using 4 (1.50 g, 5.2 mmol), 4-ethynyltoluene (0.91 g, 8 mmol and THF
(75 mL) in the general procedure gave, after 5 h, the title compound as light

Routes to Sydnone-Containing Oligomeric Areneynes
645
yellow microcrystals (1.14 g, 79%), m.p. 100–1018C. (Found: C, 73.64; H,
4.37; N, 10.07. Calc. for C17H12N2O2: C, 73.90; H, 4.38; N, 10.14); nmax
(KBr): 3150, 3079, 2913, 2215, 1732, 1508, 1466, 1361, 1006, 937, 728,
1
670 cm21; H NMR (CDCl3): d 7.8–7.1 (m, 9H), 6.9 (s, 1H), 2.4 (s, 3H);
13C NMR (CDCl3): 169.1 (C55O), 140.3, 135.2, 134.1, 132.2, 131.9, 129.6,
129.5, 125.0, 119.5, 118.4, 98.3, 97.5 (sydnone C-4), 82.1, 21.9 (CH3) ppm.
3-(2-(4-Pentylphenylethynyl)phenyl)sydnone (10)
Using 4 (1.01 g, 3.5 mmol), 1-ethynyl-4-pentylbenzene (0.89 g, 5 mmol) and
THF (50 mL) in the general procedure gave, after 4 h, elution with 10%
dichloromethane/hexanes to 1% THF/dichloromethane and recrystalization
from diethyl ether/hexanes, the title compound as yellow flakes (1.01 g,
86%), m.p. 49–508C. (Found: C, 75.98; H, 6.36; N, 8.55. Calc. for
C21H20N2O2: C, 75.88; H, 6.06; N, 8.43); nmax (KBr): 3150, 2955, 2220,
1
1735, 1508, 1465, 1350, 1219, 1167, 1006, 934, 831, 728 cm21; H NMR
(CDCl3): d 7.8–7.2 (m, 8H), 6.9 (s, 1H), 2.63–2.58 (t, 2H), 1.63–1.29
(m, 9H); 13C NMR (CDCl3): 169.1 (C55O), 145.4, 135.2, 134.1, 132.2,
131.9, 129.5, 129.0, 125.0, 119.5, 118.6, 98.4, 97.5 (sydnone C-4), 82.1,
36.2, 31.6, 31.1, 22.7, 14.3 ppm.
3-(2-(Trimethylsilylethynyl)phenyl)sydnone (11)
Using 4 (3.20 g, 0.011 mol), trimethylsilyl acetylene (1.67 g, 0.017 mol) and
THF (160 mL) in the general procedure gave, after 15 h and a modified
work-up, involving pouring into water (100 mL), extraction with dichloro-
methane (3 Â 100 mL), drying the combined extracts over magnesium
sulfate and evaporation in vacuo, followed by column chromatography and
recrystalization, the title compound as tan needles (1.89 g, 66%), m.p. 79–
808C. (Found C, 60.40; H, 5.41; N, 10.76. Calc. for C13H14N2O2Si: C,
60.44; H, 5.46; N, 10.84); nmax (KBr): 3167, 3072, 2961, 2157, 1776, 1745,
1494, 1382, 1253, 1173, 1008, 946, 851, 645 cm21 1H NMR (CDCl3):
;
d 7.68–7.65 (d, 1H), 7.60–7.51 (m, 3H), 6.80 (s, 1H), 0.19 (s, 9H); 13C
NMR (CDCl3): 168.6 (C55O), 135.6, 134.2, 131.8, 129.7, 124.6, 118.8,
104.6 (sydnone C-4), 97.3, 97.2, 20.6 (Si(CH3)3) ppm.
3-(2-Ethynylphenyl)sydnone (1)
3-(2-(Trimethylsilylethynyl)phenyl)sydnone (11) (0.110 g, 0.426 mmol) and
potassium carbonate (0.160 g, 1.0 mmol) were suspended in a mixture of
methanol/dichloromethane (3:1, 15 mL). After 3 h, the reaction was poured
into water (15 mL), extracted with dichloromethane (2 Â 50 mL), dried over
anhydrous MgSO4, and the solvent removed in vacuo to yield a brown solid
(0.079 g, 99%). Column chromatography (silica gel, dichloromethane) gave

646
A. J. Weisner, T. M. Cooper, and K. Turnbull
a tan solid (0.057 g, 71%). Recrystalization from dichloromethane/hexanes
gave the title compound as fine, tan needles (0.039 g, 49%), m.p. 133–
1348C. (Found C, 64.14; H, 3.24; N, 14.76. Calc. for C10H6N2O2: C, 64.52;
H, 3.25; N, 15.05); nmax (KBr): 3242, 3113, 3068, 2105, 1751, 1602, 1499,
1
1357, 1292, 1122, 949, 769 cm21; H NMR (CDCl3): d 7.79–7.76 (m, 1H),
7.69–7.63 (m, 3H), 6.86 (s, 1H), 3.43 (s, 1 H); 13C NMR (CDCl3): 168.8
(C55O), 135.7, 134.9, 132.0, 130.3, 125.0, 117.8, 97.5 (sydnone C-4), 85.8,
76.8 ppm.
General Procedure for the One-Pot Desilylation of
3-(2-(Trimethylsilylethynyl)phenyl)-sydnone (11) and
Coupling with Substituted Aryl Iodides to Give 8, 12–16
Tetrabutylammonium fluoride (1.1 mL, 1.1 mmol, 1.0 M in THF) was added
dropwise to a solution of 3-(2-(trimethylsilylethynyl)phenyl)sydnone (11)
(0.258 g, 1.0 mmol) dissolved in dry THF (15 mL). Ten minutes after this
addition, triethylamine (0.506 g, 0.7 mL, 0.005 mol), and the aryl iodide
(0.0011 mol) were added. The reaction was deoxygenated, then bis triphenyl-
phosphine palladium dichloride (5 mol%) was added and the reaction allowed
to stir for 10 minutes, followed by the addition of copper (I) iodide (10 mol%).
The solution was stirred at room temperature for a further 1 to 4 h, whereupon
it was poured into water (20 mL), extracted with dichloromethane
(3 Â 50 mL), dried over anhydrous MgSO4, and the solvent removed in
vacuo. Column chromatography followed by recrystalization gave 8, 12–16.
3-(2-(Phenylethynyl)phenyl)sydnone (8)
Using iodobenzene in the general procedure, followed by column chromato-
graphy (dichloromethane) and recrystalization from dichloromethane/
hexanes, gave the title compound as white plates (0.171 g, 67%), m.p.
74–758C, identical (TLC, IR) to an authentic sample prepared as described
previously.
3-(2-(4-Aminophenylethynyl)phenyl)sydnone (12)
Using 4-iodoaniline in the general procedure, followed by column chromato-
graphy (silica gel, dichloromethane to 4% ethyl acetate/dichloromethane) and
recrystalization from methanol/water, gave the title compound as yellow
needles, (0.076 g, 27%), m.p. 126–1278C. (Found C, 69.13; H, 4.21; N,
14.95. Calc. for C16H11N3O2: C, 69.31; H, 4.00; N: 15.15); nmax (KBr):
3482, 3347, 3209, 3157, 3062, 3034, 2209, 1737, 1625, 1596, 1516, 1471,
1
1430, 1303, 1146, 943, 830, 761, 696, 524 cm21; H NMR (CDCl3): d 7.4–
7.8 (m, 4H), 7.1–7.3 (d, 2H), 6.9 (s, 1H), 6.5–6.7 (d, 2H), 3.95, (brd, s, 2H);

Routes to Sydnone-Containing Oligomeric Areneynes
647
13C NMR (CDCl3): 169.2 (C55O), 148.2, 134.9, 133.7, 132.1, 128.8, 124.9,
120.0, 114.9, 110.4, 97.6 (sydnone C-4), 99.4, 81.1 ppm.
3-(2-(4-Nitrophenylethynyl)phenyl)sydnone (13)
Using 4-nitro-1-iodobenzene in the general procedure, followed by column
chromatography (silica gel, 30% hexanes/dichloromethane to dichloro-
methane) and recrystalization from dichloromethane/hexanes, gave the title
compound as a colorless, amorphous solid (0.167 g, 54%), m.p. 158–1598C.
(Found C, 62.27; H, 3.09; N, 13.39. Calc. for C16H9N3O4: C, 62.54; H,
2.95; N, 13.68); nmax (KBr): 3168, 3105, 2926, 2437, 1787, 1753, 1591,
1
1516, 1499, 1426, 1340, 1290, 1162, 1068, 936, 867, 726, 669 cm21; H
NMR (CDCl3): d 8.2–8.4 (d, 2H), 7.7–7.9 (d, 1H), 7.4–7.7 (m, 5H), 6.8
(s, 1H); 13C NMR (CDCl3): 168.9 (C55O), 148.0, 135.6, 134.4, 132.8,
132.5, 130.9, 128.2, 125.3, 124.0, 118.3, 97.4 (sydnone C-4), 94.9, 87.0 ppm.
3-(2-(4-Acetylphenylethynyl)phenyl)sydnone (14)
Using 1-acetyl-4-iodobenzene in the general procedure, followed by
column chromatography (silica gel, dichloromethane to 4% ethyl acetate/
dichloromethane) and recrystalization from dichloromethane/hexanes, gave
the title compound as light tan plates (0.193g, 63%), m.p. 137–1398C.
(Found C, 70.89; H, 4.07; N, 9.11. Calc. for C18H12N2O3: C, 71.05; H, 3.97;
N, 9.21); nmax (KBr): 3169, 3135, 3118, 3074, 2976, 2218, 2108, 1875, 1787,
1765,1736, 1679, 1556, 1471, 1358, 1223, 1167, 1110, 959, 830, 726,
1
632 cm21; H NMR (CDCl3): d 7.96–7.90 (d of t, 2H), 7.82–7.78 (d, 1H),
7.71–7.57 (m, 3H), 7.55–7.49 (d of t, 2H), 6.8 (s, 1H), 2.6 (s, 3H); 13C NMR
(CDCl3): 197.3, 169.9 (sydnone C55O), 137.4, 135.5, 134.3, 132.3, 132.2,
130.3, 128.7, 126.2, 125.2, 118.8, 97.5 (sydnone C-4), 96.5, 85.3, 26.9ppm.
3-(2-(4-Methoxyphenylethynyl)phenyl)sydnone (15)
Using 4-iodoanisole in the general procedure, followed by column chromato-
graphy (silica gel, dichloromethane to 2% ethyl acetate/dichloromethane) and
recrystalization from dichloromethane/hexanes, gave the title compound as
light yellow plates (0.123 g, 42%), m.p. 146–1498C. (Found C, 69.51; H,
4.17; N, 9.51. Calc. for C17H12N2O3: C, 69.86; H, 4.14; N, 9.58); nmax
(KBr): 3152, 3068, 2986, 2215, 1780, 1752, 1596, 1467, 1360, 1288, 1169,
1
1025, 938, 827, 770, 673 cm21; H NMR (CDCl3): d 7.78–7.34 (m, 6H),
6.92–6.82 (m, 3H), 3.82 (s, 3H); 13C NMR (CDCl3): 169.1 (sydnone
C55O), 160.9, 135.1, 133.9, 133.6, 132.1, 129.3, 125.0, 119.7, 114.6, 113.5,
98.3, 97.5 (sydnone C-4), 81.6, 55.6 ppm.

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A. J. Weisner, T. M. Cooper, and K. Turnbull
3-(2-(4-Bromophenylethynyl)phenyl)sydnone (16)
Using 1-bromo-4-iodobenzene in the general procedure, followed by
column chromatography (silica gel, 10% hexanes/dichloromethane) and
recrystalization from dichloromethane/hexanes, gave the title compound as
tan needles (0.244 g, 72%), m.p. 110–1118C. (Found C, 56.17; H, 2.84; N,
8.17. Calc. for C16H9BrN2O2: C, 56.33; H, 2.66; N, 8.21); nmax (KBr):
3117, 3038, 2216, 1753, 1502, 1433, 1354, 1223, 1173, 1068, 943, 824,
765, 725 cm21 1H NMR (CDCl3): d 7.73–7.80 (d, 1H), 7.54–7.69
;
(m, 3H), 7.45–4.52 (d, 4H), 6.86 (s, 1H); 13C NMR (CDCl3): 169.0
(C55O), 135.4, 134.2, 133.4, 132.3, 132.2, 130.0, 125.2, 124.4, 120.1,
119.0, 97.4 (sydnone C-4), 96.6, 83.6 ppm.
3-(2-(4-(Trimethylsilylethynyl)phenylethynyl)phenyl)sydnone (17)
3-(2-(4-Bromophenylethynyl)phenyl)sydnone (16) (0.218 g, 0.638 mmol),
triethylamine (0.097 g, 0.957 mmol), and trimethylsilylacetylene (0.09 g,
0.957 mmol) were dissolved in THF (10 mL), and the solution was deoxyge-
nated. The reaction was heated to 508C. Bis triphenylphosphinepalladium
dichloride (0.020 g, 0.028 mmol) was added, the reaction was stirred for
10 min, and this was followed by the addition of copper(I) iodide (0.002 g,
0.011 mmol). After heating overnight, the solvent was removed in vacuo
to yield a dark oil. Column chromatography (silica gel, 10% hexanes/
dichloromethane to dichloromethane) gave a yellow solid (0.192 g, 84%).
Recrystalization from boiling dichloromethane gave the title compound as
fine white needles (0.101 g, 44%), m.p. 147–1498C. (Found C, 69.53; H,
.
5.19; N, 7.49. Calc. for C21H18N2O2Si 1/4 H2O: C, 69.48; H, 5.14; N:
7.72); nmax (KBr): 3155, 3040, 2899, 2220, 2160, 1765, 1750, 1598, 1432,
1
1247, 1163, 1077, 881, 757 cm21; H NMR (CDCl3): d 7.78–7.35 (m, 8H),
6.87 (s, 1H), 0.26 (s, 9H); 13C NMR (CDCl3): 169.0 (C55O), 135.3, 134.2,
132.3, 132.2, 131.7, 129.9, 125.1, 124.6, 121.4, 119.1, 104.4, 97.6, 97.4
(sydnone C-4), 97.3, 84.3, 0.11 ppm.
3-(2-(4-(Ethynyl)phenylethynyl)phenyl)sydnone (2)
Tetrabutylammonium fluoride (0.5 mL, 0.5.0 mmol, 1.0 M in THF) was added
dropwise to a solution of 3-(2-(4-(trimethylsilylethynyl)phenylethynyl)
phenyl)sydnone (17) (0.150 g, 0.418 mmol) in THF (15 mL). After 10 min,
the reaction was poured into water (15 mL), extracted with dichloromethane
(3 Â 50 mL), dried over anhydrous MgSO4, and the solvent removed in
vacuo to yield a brown solid. Column chromatography (silica gel, dichloro-
methane) gave a light brown solid (0.56 g, 47%). Recrystalization from
boiling dichloromethane gave the title compound as a tan amorphous solid
(0.045 g, 38%), m.p. 1768C (dec). (Found C, 74.05; H, 3.55; N: 9.50. Calc.

Routes to Sydnone-Containing Oligomeric Areneynes
649
.
for C18H10N2O2 1/4 H2O: C, 74.34; H, 3.64; N, 9.64); nmax (KBr): 3224,
3168, 3068, 3041, 2221, 1774, 1752, 1503, 1472, 1354, 1263, 1167, 1077,
939, 840 cm21 1H NMR (CDCl3): d 7.8–7.2 (m, 8H), 6.9 (s, 1H), 3.2
;
(s, 1H); 13C NMR (CDCl3): 169.0 (C55O), 135.4, 134.2, 132.5, 132.3,
131.9, 130.0, 125.1, 123.6, 121.8, 119.1, 97.4 (sydnone C-4), 97.0, 84.3,
83.2, 80.0 ppm.
3-(2-(4-(4-(Bromophenyl)ethynyl)phenylethynyl)phenyl)sydnone (18)
3-(2-(4-(Ethynyl)phenylethynyl)phenyl)sydnone (2) (0.287 g, 1.0 mmol),
1-bromo-4-iodobenzene (0.30 g, 1.05 mmol), and triethylamine (0.506 g,
0.7 mL, 5.0 mmol) were dissolved in THF (15 mL). The reaction solution
was deoxygenated, bistriphenylphosphinepalladium dichloride (0.040 g,
0.05 mmol) was added and the reaction allowed to stir for 10 minutes,
followed by the addition of copper(I) iodide (0.020 g, 0.1 mmol). The
reaction was stirred at room temperature for a further 4 h, whereupon it was
poured into water (20 mL), extracted with dichloromethane (3 Â 50 mL),
dried over anhydrous MgSO4, and the solvent removed in vacuo to give
a dark brown semi-solid. Column chromatography (silica gel, 30%
hexanes/dichloromethane) gave a yellow-orange solid (0.347 g, 79%).
Recrystalization from boiling dichloromethane gave the title compound as
yellow plates (0.187 g, 42%), m.p. 202–2048C. (Found C, 65.11; H, 3.05;
N, 6.25. Calc.for C24H13BrN2O2: C: 65.32, H: 2.97, N: 6.35); nmax (KBr):
3116, 2216, 2108, 1754, 1510, 1433, 1357, 1225, 1172, 1069, 824,
765 cm21 1H NMR (CDCl3): d 7.82–7.36 (m, 12H), 6.89 (s, 1H); 13C
;
NMR (CDCl3): 169.0 (C55O), 135.4, 134.2, 133.3 132.3, 132.0, 131.9,
130.0, 125.1, 124.5, 123.2, 122.0, 121.4, 119.1, 97.4 (sydnone C-4), 97.3,
91.2, 90.1, 84.3 ppm.
General Procedure For the Two Reaction, One-Pot Syntheses of the
Terminal Alkynes 2 and 3 from the Corresponding Bromophenyl
Precursors 16 and 18, Respectively
The bromo compound 16 or 18 (2.0 mmol), trimethylsilylacetylene
(0.59 g, 0.9 mL, 6.0 mmol), and triethylamine (1.01 g, 1.4 mL, 0.01 mol)
were dissolved in THF (60 mL) and the reaction solution was deoxygenated.
The reaction was heated to 508C. Bistriphenylphosphinepalladium dichloride
(5 mol%) was added, the reaction was allowed to stir for 10 min, and this
was followed by the addition of copper(I) iodide (10 mol%). After heating
overnight, the mixture was allowed to cool to room temperature and
potassium carbonate (1.27 g, 9.0 mmol) and methanol (30 mL) were added.
After stirring overnight, the reaction was poured into water (100 mL) and
extracted with dichloromethane (3 Â 100 mL). The combined extracts were

650
A. J. Weisner, T. M. Cooper, and K. Turnbull
dried over anhydrous MgSO4, and the solvent removed in vacuo to yield
a dark brown solid. Column chromatography (silica gel, 30% hexanes/
dichloromethane to 10% ethyl acetate/dichloromethane) and attempted
recrystalization from boiling dichloromethane provided the product as a
yellow powder.
3-(2-(4-(Ethynyl)phenylethynyl)phenyl)sydnone (2)
Using 3-(2-(4-Bromophenylethynyl)phenyl)sydnone (16) in the general
procedure gave the title compound (0.35 g, 61%) (0.49 g, 85.5% prior to
recrystalization), identical to a sample prepared as mentioned previously.
3-(2-(4-(4-Ethynyl)phenylethynyl)phenylethynyl)phenyl)sydnone (3)
Using 3-(2-(4-(4-(Bromophenyl)ethynyl)phenylethynyl)phenyl)sydnone (18)
in the general procedure gave the title compound (0.280 g, 36%) [0.630 g,
81% prior to recrystalization], m.p. 2208C (chars; does not melt up to
.
4008C). (Found C, 79.86; H, 3.80; N, 6.93. Calc. for C26H14N2O2 1/4
H2O: C, 79.88; H, 3.74; N, 7.16); nmax (KBr): 3293, 3115, 3038, 2218,
1
2106, 1756, 1600, 1515, 1433, 1357, 1224, 1171, 1006, 941, 838 cm21; H
NMR (CDCl3): d 7.9–7.3 (m, 11H), 6.9 (s, 1H), 3.2 (s, 1H); 13C NMR
(CDCl3): 169.0 (C55O), 135.4, 134.2, 132.4, 132.3, 132.0, 132.0, 131.8,
129.9, 125.1, 124.5, 123.5, 122.5, 121.4, 119.1, 97.5 (sydnone C-4), 97.3,
91.7, 90.9, 84.3, 83.4, 79.4 (terminal acetylene carbon) ppm.
Three Reaction, One-Pot Synthesis of 3-(2-(4-Bromophenylethynyl)
phenyl)sydnone (16) from 3-(2-Iodophenyl)sydnone (4)
3-(2-Iodophenyl)sydnone (4) (3.20 g, 11.0 mmol), trimethylsilylacetylene
(1.67 g, 2.4 mL, 17.0 mmol), and triethylamine (5.57 g, 7.6 mL, 0.055 mol)
were dissolved in dry THF (160 mL) and the solution was deoxygenated. Bis-
triphenylphosphinepalladium dichloride (0.40 g, 0.55 mmol) was added and
the reaction was allowed to stir for 10 minutes, followed by the addition of
copper(I) iodide (0.20 g, 1.1 mmol). The solution was heated at 508C
overnight, whereupon the reaction was allowed to cool. Tetrabutylammonium
fluoride (17 mL, 17 mmol, 1.0 M in THF) was added dropwise and the reaction
was allowed to stir for 10 minutes. 1-Bromo-4-iodobenzene (3.31 g,
12.0 mmol) was added, and the reaction allowed to stir at room temperature
for four hours, whereupon it was poured into water (100 mL), extracted
with dichloromethane (3 Â 100 mL), dried over anhydrous MgSO4, and the
solvent removed in vacuo to yield a black, semi-solid. Column chromato-
graphy (silica gel, 30% hexanes/dichloromethane to dichloromethane) gave

Routes to Sydnone-Containing Oligomeric Areneynes
651
the title compound as a golden-brown solid (2.86 g, 76%), identical (TLC, IR)
to an authentic sample prepared as described earlier.
Three Reaction, One Pot Synthesis of 3-(2-(4-(4-(Bromophenyl)
ethynyl)phenylethynyl)phenyl)sydnone (18) from 3-(2-(4-
Bromophenylethynyl)phenyl)sydnone (16)
3-(2-(4-Bromophenylethynyl)phenyl)sydnone (16) (2.62 g, 8.0 mmol), tri-
methylsilyl acetylene (2.26 g, 3.3 mL, 0.023 mol) and triethylamine (3.88 g,
5.3 mL, 0.038 mol), were dissolved in THF (120 mL), and the solution was
deoxygenated.
Bistriphenylphosphinepalladium
dichloride
(0.270 g,
0.38 mmol) was added, the reaction was allowed to stir for 10 minutes, and
this was followed by the addition of copper(I) iodide (0.150 g, 0.77 mmol).
The solution was heated at 508C overnight whereupon it was allowed to
cool to room temperature. Tetrabutylammonium fluoride (25 mL, 0.025
mol, 1.0 M in THF) was added dropwise and, after 1 h, 1-bromo-4-
iodobenzene (2.28 g, 80 mmol) was added. The reaction was allowed to stir
at room temperature overnight whereupon it was poured into water
(100 mL), extracted with dichloromethane (3 Â 100 mL), dried over
anhydrous MgSO4, and the solvent removed in vacuo to yield a black tar.
Column chromatography (silica gel, 30% hexanes/dichloromethane) gave
the title compound as a tan-yellow solid (1.81 g, 51%), identical (TLC, IR)
to an authentic sample, prepared as described earlier.
ACKNOWLEDGMENTS
The authors gratefully acknowledge the WSU Graduate Council for a scholar-
ship to AJW, Aaron Burke for the NMR spectra, the Air Force Research
Laboratory and the Petroleum Research Fund, administered by the
American Chemical Society, for partial support of this research.
REFERENCES
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