Synthesis of new diethynylbenzene derivatives

Article abstract of DOI:10.1081/SCC-200025604

The preparation of new monomeric diacetylenic aromatic compounds is described.

Full text of DOI:10.1081/SCC-200025604

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Synthesis of New
Diethynylbenzene Derivatives
F. Chimenti a , A. Bolasco a , D. Secci a , P.
Chimenti a & A. Granese a
a Dipartimento di Studi di Chimica e Tecnologia
delle Sostanze Biologicamente Attive , Università
degli Studi di Roma “La Sapienza” , P. le A. Moro
5, 00185, Roma, Italy
Published online: 10 Jan 2011.
To cite this article: F. Chimenti , A. Bolasco , D. Secci , P. Chimenti & A. Granese
(2004) Synthesis of New Diethynylbenzene Derivatives, Synthetic Communications:
An International Journal for Rapid Communication of Synthetic Organic Chemistry,
34:14, 2549-2555, DOI: 10.1081/SCC-200025604
To link to this article: http://dx.doi.org/10.1081/SCC-200025604
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 14, pp. 2549–2555, 2004
Synthesis of New Diethynylbenzene
Derivatives
*
F. Chimenti, A. Bolasco, D. Secci, P. Chimenti,
and A. Granese
Dipartimento di Studi di Chimica e Tecnologia delle Sostanze
`
Biologicamente Attive, Universita degli Studi di
Roma “La Sapienza”, Roma, Italy
ABSTRACT
The preparation of new monomeric diacetylenic aromatic compounds is
described.
INTRODUCTION
Diacetylenes have been the object of great interest and extended research,
because upon polymerization they can give rise to extended conjugated
p-systems. A number of different polymers can be obtained from the poly-
merization of diacetylene monomers, depending on the relative position of
*
Correspondence: A. Bolasco, Dipartimento di Studi di Chimica e Tecnologia delle
`
Sostanze Biologicamente Attive, Universita degli Studi di Roma “La Sapienza”, P. le
A. Moro 5, 00185 Roma, Italy; E-mail: adriana.bolasco@uniroma1.it.
2549
DOI: 10.1080/SCC-200025604
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

2550
Chimenti et al.
the two triple bonds in the monomer. The resulting polyacetylenes have
physical and chemical properties[1] that make them interesting materials for
use in electronics, optics, biophysics,[2] biochemistry, and time-temperature
devices.[3]
Diethynylbenzene derivatives could be considered important monomers
in the synthesis of potentially conducting polymers. Knowing that the electric
conductivity of polymers depends on the nature of the substituents of the
benzene ring, it is interesting to synthesize diethynylbenzene derivatives in
order to study the substituent effect on the characteristics of the polymer.
For these reasons, following our interest in the preparation and charac-
terization of potentially conducting polymers related to polydiethynyl
benzenes,[4–7] we report, here, the preparation of the new monomeric diace-
tylenic aromatic compounds, 3a–d, bearing different substituents, which
can be used as precursors of polymers and which are, moreover, of interest
in their own right as unusual ethynylated compounds.
The diethynylbenzene derivatives (3a–d) were synthesized as depicted in
Sch. 1 using Pd/Cu-catalyzed coupling of a silylating agent with an aryl
iodide according to a similar procedure by Horn et al.[8] We have chosen
the (trimethylsilyl)acetylene as silylating agent, because it can be quantita-
tively removed by treatment with dilute alkali.
The trimethylsilyl-protected ethynyl aromatics (2a–d) are very stable
intermediates, and it has been possible to isolate and characterize them in
this work. The mass fragmentation pattern of intermediates, 2a–d, whose
analytical data are reported in Table 1, together with those of compounds
1c and 3a–d, supports the assigned structures: they generally exhibit an
intense molecular ion (100%) and a characteristic fragmentation ion at
M-15 corresponding to a methyl group loss. Compounds 2a and 3a have
been reported previously,[9] but no data have been published.
A mild basic hydrolysis of intermediates 2a–d is sufficient to remove the
TMS group affording diethynyl derivatives 3a–d, whose mass spectra show
an intense molecular ion (100%).
Scheme 1.

New Diethynylbenzene Derivatives
2551

2552
Chimenti et al.
EXPERIMENTAL
Melting points were obtained on a Bu¨chi 510 Melting Point Apparatus
and are uncorrected. Analytical TLCs were run on commercial Merck plates
1
coated with silica gel G/UV 254 nm (0.20-mm thick).The H-NMR spectra
were recorded on a Bruker AM-400 (400 MHz) FT spectrometer and the
chemical shifts were reported in ppm referring to the solvent peak. The IR
spectra were performed on a Perkin–Elmer 1605 FT spectrophotometer on
potassium bromide mulls. The electron impact mass spectral data were
obtained with a Saturn 2000 GC/MS using a CP-SIL5 CB Low Bleed/MS
30 m, 0.25 ID column and EI at 70 eV. Elemental analyses for C, H, and N
were performed on a Carlo Erba model 1106 elemental analyzer, and the
analytical results were within +0.4% of the theoretical values.
Unless otherwise specified, all reagents and solvents were obtained from
Aldrich Chemical, and were used without any further purification.
The 3,5-diiodonitrobenzene 1a, which is not commercially available,
was prepared according to the literature.[10] The 3,5-diiodoaniline 1c was
obtained by catalytic hydrogenation of 1a in EtOH at 158C using Raney-
Nickel as catalyst.[11] Commercial 2,6-diiodo-4-nitrophenol 1b and 2,6-
diiodo-4-nitroaniline 1d were purified with acetone, acetic acid, and diethyl-
ether, and then filtered as yellow crystals m.p. 251–2538C and
155–1578C, respectively. Bis(Triphenylphosphine)palladium(II)chloride was
purified by crystallization from chloroform. Diisopropylamine was freshly
distilled.
General Procedure for the Synthesis of bis(Trimethylsilyl)-
Ethynyl Derivatives 2a–d
bis(Triphenylphosphine)palladium(II)dichloride (BTPP/PdCl2) (0.35 g,
0.49 mmol) and copper(II)acetate (0.1 g, 0.50 mmol) were added to a solution
of 1a–d (0.020 mmol) in 50 mL of diisopropylamine. The solution was
degassed by flowing nitrogen through it, and then 3.1 mL (21.93 mmol) of
(trimethylsilyl)acetylene (TMSA) was added. The solution was kept under
stirring at room temperature for 1 hr. The solution was then filtered to
remove the precipitate of diisopropylamine hydroiodide salts, and the
solvent was removed under reduced pressure. The crude residue was dis-
solved in dichloromethane, extracted first with 5% HCl solution, then with
water, and dried to give the Bis(trimethylsilyl)-ethynyl derivatives 2a–d
after distillation of the solvent. Compounds 2a–d were purified by column
chromatography (silica gel, hexanes : diethylether 20 : 1 as eluent) and
crystallized from ethanol.

New Diethynylbenzene Derivatives
2553
2a. 1H-NMR (CD3COCD3): d ¼ 8.54 (s, 2H, Ar-H), 8.30 (s, 1H, Ar-H),
0.26 (s, 18H, 6CH3). 13C-NMR: d ¼ 147.6 (C-1), 141.8 (C-4), 126.9 (C-2 and
;;
;;
C-6), 122.8 (C-3 and C-5), 85.0 (C ), 78.0 ( C–Si), 21.0 (CH3).
2b. 1H-NMR (CD2Cl2): d ¼ 8.16 (s, 2H, Ar-H), 4.30 (s, broad, 1H, OH,
D2O exch.), 0.26 (s, 18H, 6CH3). 13C-NMR: d ¼ 170.2 (C-1), 140.2 (C-4),
;;
;;
128.3 (C-3 and C-5), 110.0 (C-2 and C-6), 85.0 (C ), 78.0 ( C–Si),
21.0 (CH3).
2c. 1H-NMR (CD3COCD3): d ¼ 7.15 (s, 2H, Ar-H), 6.56 (s, 1H, Ar-H),
3.60 (s, broad, 2H, NH2, D2O exch.), 0.26 (s, 18H, 6CH3). 13C-NMR:
d ¼ 153.9 (C-1), 132.6 (C-3 and C-5), 117.7 (C-4), 108.5 (C-2 and C-6),
;;
;;
85.0 (C ), 78.0 ( C–Si), 21.0 (CH3).
2d. 1H-NMR (CD3COCD3): d ¼ 8.12 (s, 2H, Ar-H), 5.50 (s, broad, 2H,
NH2, D2O exch.), 0.26 (s, 18H, 6CH3). 13C-NMR: d ¼ 160.0 (C-1), 137.6 (C-
;;
4), 127.7 (C-3 and C-5), 109.4 (C-2 and C-6), 85.0 (C ), 78.0 ( C–Si),
;;
21.0 (CH3).
General Procedure for the Synthesis of Diethynylbenzene
Derivatives 3a–d
An excess of 1% KOH solution was added to a solution of bis(trimethyl-
silyl)-ethynyl derivatives 2a–d (mmol) in 80 mL of methanol to remove the
trimethylsilyl groups. After 20 min, the volume of the resulting solution was
reduced, diluted with water, extracted with chloroform, and dried over
sodium sulfate. After distillation of the solvent, the crude solid was column
chromatographed (silica gel, diisopropylether : hexanes 2 : 1 as eluent) and
crystallized from benzene to give the pure diethynyl derivatives 3a–d.
3a. 1H-NMR (CD3COCD3): d ¼ 8.33 (s, 2H, Ar-H), 7.97 (s, 1H, Ar-H),
4.23 (s, 2H, 2CH). 13C-NMR: d ¼ 147.6 (C-1), 141.8 (C-4), 126.9 (C-2 and
;;
;;
C-6), 122.8 (C-3 and C-5), 84.6 (C ), 78.3 ( CH); GC-MS: m/z ¼ 171
[Mþ]; 155 [Mþ 2 O]; 141 [Mþ 2 NO]; 125 [Mþ 2 NO2].
3b. 1H-NMR (CD2Cl2): d ¼ 8.52 (s, 2H, Ar-H), 6.30 (s, broad, 1H, OH,
D2O exch.), 3.06 (s, 2H, 2CH). 13C-NMR: d ¼ 170.6 (C-1), 140.2 (C-4), 128.3
;;
;;
(C-3 and C-5), 110.0 (C-2 and C-6), 84.6 (C ), 78.3 ( CH). GC-MS:
m/z ¼ 187 [Mþ]; 171 [Mþ 2 O]; 157 [Mþ 2 NO]; 141 [Mþ 2 NO2].
3c. 1H-NMR (CD3COCD3): d ¼ 7.15 (s, 2H, Ar-H), 6.56 (s, 1H, Ar-H),
4.70 (s, broad, 2H, NH2, D2O exch.), 4.23 (s, 2H, 2CH). 13C-NMR: d ¼ 153.9
;;
(C-1), 132.6 (C-3 and C-5), 117.7 (C-4), 108.5 (þC-2 and C-6), 84.6 (C ),
þ
;;
78.3 ( CH). GC-MS: m/z ¼ 141 [M ]; 114 [M 2 HCN].
3d. 1H-NMR (CD3COCD3): d ¼ 8.08 (s, 2H, Ar-H), 6.78 (s, broad, 2H,
NH2, D2O exch.), 4.67 (s, 2H, 2CH). 13C-NMR: d ¼ 160.0 (C-1), 137.6 (C-4),

2554
Chimenti et al.
;;
127.7 (C-3 and C-5), 109.4 (C-2 and C-6), 84.6 (C ), 78.3 ( CH). GC-MS:
;;
m/z ¼ 186 [Mþ]; 170 [Mþ 2 O]; 156 [Mþ 2 NO]; 140 [Mþ 2 NO2].
ACKNOWLEDGMENT
This work was in part supported by grants from MURST.
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Received in Poland March 2, 2004