Oligo(1,4-phenylenepyrazole-3,5-diyl)s

Article abstract of DOI:10.1002/ejoc.200300221

The bifunctional nucleophile methylhydrazine reacts in an alkaline medium in a regioselective mode with chalcones to yield 2-pyrazolines, which can be oxidized by DDQ to the corresponding 1H-pyrazoles. From oligo(chalcone)s this reaction yields cross-conjugated compounds with an alternating sequence of 1,4-disubstituted benzene rings and 3,5-disubstituted 1H-pyrazole rings. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejoc.200300221

FULL PAPER
Oligo(1,4-phenylenepyrazole-3,5-diyl)s
Herbert Meier*[a] and Angelina Hormaza[a]
Keywords: Conjugation / Heterocycles / Oligomers / Regioselectivity / Ring closure
The bifunctional nucleophile methylhydrazine reacts in an
alkaline medium in a regioselective mode with chalcones to
yield 2-pyrazolines, which can be oxidized by DDQ to the
ing sequence of 1,4-disubstituted benzene rings and 3,5-di-
substituted 1H-pyrazole rings.
corresponding 1H-pyrazoles. From oligo(chalcone)s this re- ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
action yields cross-conjugated compounds with an alternat- Germany, 2003)
Introduction
further to 1H-pyrazoles.[7Ϫ19] Very recently, Silva, Elguero
and co-workers reported on a route that is based on di-
bromo adducts of the enones.[20] Since α,β-unsaturated ke-
tones are bifunctional electrophiles and monosubstituted
hydrazines are unsymmetric bifunctional nucleophiles, there
are altogether four possibilities for the initial attack, for-
ming two isomeric 1H-pyrazoles as a result (Scheme 1). The
selectivity of the process depends on the steric and elec-
tronic effects of the two components and on the reaction
conditions[8,10,11,13,15], the latter influencing particularly the
reversion of the regioselectivity.[8] The often discussed
alternative between 1,2- and 1,4-addition[10,13,15] is some-
what misleading; we suggest in Scheme 2 that in an alkaline
medium N-1 of methylhydrazine (2) attacks C-3 of the en-
one. Thus, a stabilized anion 3 is generated which cyclizes
to the 2-pyrazoline 4. In the protic solvent methanol the
process is more complicated. Apart from the Michael-type
addition 1Ј ϩ 2 Ǟ 3Ј, the intermediate formation of an N-
methylhydrazone 3ЈЈ can take place. Cyclization then again
leads to 4 which is oxidized by DDQ to the 1H-pyrazole 6.
Monitoring the reaction by 1H NMR spectroscopy in
CD3OD revealed that after the addition of 1 and 2 a new
Conjugated or cross-conjugated oligomers, which consist
of arylene or hetarylene building blocks, represent an area
of wide current interest in organic synthesis and materials
science.[1] Some time ago we reported on oligo-
(chalcone)s[2Ϫ4] and their transformation to oligo(p-phenyl-
ene-m-pyridinediyl)s.[5] The enone substructure is suitable
for the generation of heterocycles with five-, six- and seven-
membered rings.[6] We have now studied the formation of
1,4-phenylene-3,5Ϫ1H-pyrazolediyl units B from 1,4-phen-
ylene-1,3-propenoylene units A in oligomers. Scheme 1 il-
lustrates that the reaction with hydrazine derivatives and
subsequent oxidation with 2,3-dichloro-5,6-dicyano-p-
benzoquinone can principally lead to regioisomers B and
BЈ. Only for R ϭ H, does a fast tautomeric equilibrium B
ǟ
Ǟ
BЈ exist.
3
olefinic AB system is formed with a Jtrans coupling con-
stant of 16.3 Hz, which we attribute to 3ЈЈ. Since at least
three NCH3 singlet signals can be observed, which do not
belong to 2 or 4, we assume, that the reaction route 1Ј ϩ 2
Ǟ 3Ј Ǟ 4 competes with the reaction route 1Ј ϩ 2 Ǟ 3ЈЈ
Ǟ 4.
The same procedures, applied to enone 7, gave the 1H-
pyrazole 9 via the 2-pyrazoline 8 (Scheme 3). The yields are
generally somewhat higher for alkaline catalysis than for the
reaction in methanol.
Scheme 1. Formation of phenylene-1H-pyrazolediyl repeat units
from chalcone building blocks
Results and Discussion
There are several methods in the literature for the trans-
formation of enones with hydrazines to pyrazolines and
After these primary experiments, we were surprised by
the reactivity of the bis(chalcone) 10. The variant in meth-
anol yielded, after oxidation, compounds 11 and 12 in a
ratio of 46:54. In contrast to the chalcones 1 and 7, one
enone unit of 10 can react with the opposite regioselectivity.
Moreover, the structure of the major product 12 differs
[a]
Institut für Organische Chemie der Johannes Gutenberg-
Universität Mainz,
Duesbergweg 10Ϫ14, 55099 Mainz, Germany
Fax: (internat.) ϩ49-(0)6131/3925396
E-mail: hmeier@mail.uni-mainz.de
3372
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejoc.200300221
Eur. J. Org. Chem. 2003, 3372Ϫ3377

Oligo(1,4-phenylenepyrazole-3,5-diyl)s
FULL PAPER
Scheme 2. Reaction of the unsymmetric chalcone 1 with methylhydrazine (2) and subsequent oxidation to the 1H-pyrazole 6
1
Table 1. H NMR spectroscopic data of the compounds 9, 11, 12 and 15, δ values in CDCl3/C6D6 (1:1), TMS as internal standard (the
numbering corresponds to the nomenclature)
Compd.
3,5-Pyrazolylene
1,4-Phenylene
3-H (s)
Phenyl[a]
4-H
(dd)
Propoxy
CH2
(m)
1-CH3
4-H
(s)
3-H
(d)
6-H
(d)
OCH2
(t)
CH3
(t)
(s)
6-H (s)
9
3.63
6.96
6.67
6.64
6.72
6.76
7.81
6.82
3.54
3.62
3.67
3.75
3.57
3.71
3.77
1.43
1.60
1.60
1.62
1.41Ϫ
1.50
(4 H)
1.58Ϫ
1.67
0.70
0.85
0.83
0.85
0.71
0.85
0.87
11
3.69
7.05
6.84
6.68
6.75
7.87
(8 H)
1.45Ϫ
1.53
(4 H)
1.60Ϫ
1.70
(8 H)
1.50
1.50
12
15
3.72
3.73
7.04
7.06
6.86
7.91
6.69
6.71
6.78
6.81
7.86
6.87
3.60
3.67
3.73
3.78
3.80
3.80
3.62
3.62
3.74
3.80
3.98
0.73
0.75
0.75
0.89
0.89
0.90
0.90
0.90
0.89
0.77
0.75
3.74
3.76
7.06
7.15
6.89
6.91
7.96
6.74
6.78
7.86
1.66
1.66
1.71
[a] The upper δ values in this column belong to the phenyl group on C-3, the lower δ values to the phenyl group on C-5 of the pyrazole ring.
from the structure which was obtained for the reaction formed pyrazoline ring changes the regioselectivity for the
products of monosubstituted hydrazines and 1,4-bis(2- formation of the second pyrazoline ring. Alkaline catalysis
benzoylethenyl)benzene.[11] The propoxy groups in the en- of the reaction 10 ϩ 2 yielded pure 11. Therefore, we sub-
ones were originally introduced to enhance the solubility jected the higher oligomers 13 and 14 only to the alkaline
and for the reduction of the HOMOϪLUMO gap;[2,3] they variant. Oligochalcone 13 with four enone substructures
may have weak steric and/or electronic effects, but they can- furnishes 15 with four 1H-pyrazole units; however, the yield
not change the reactivity towards hydrazines, as examples 1 decreases to 12%, so it was not unexpected that oligochal-
and 7 demonstrate. We assume that the first regularly cone 14, with six enone units, gave only very small amounts
Eur. J. Org. Chem. 2003, 3372Ϫ3377
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H. Meier, A. Hormaza
FULL PAPER
Structure elucidation of 2-pyrazolines 4 and 8 and 1H-
pyrazoles 6, 9, 11, 12 and 15 is mainly based on 1H and 13
C
NMR measurements including two-dimensional techniques
such as TOCSY, ROESY, COSY, HMQC and HMBC.[21]
The 1H NMR spectra of 4 and 8 are characterized by AMX
spin patterns for the protons on the 2-pyrazoline ring. The
geminal coupling constant 2J (4-H, 4-H) amounts to (Ϫ16.7
3
Ϯ 0.1) Hz, the vicinal trans coupling constant Jtrans (4-H,
5-H) to (14.7 Ϯ 0.2) Hz and the vicinal cis coupling con-
3
stant Jcis (4-H, 5-H) to 9.8 Hz. The chemical shift values
are listed in the Exp. Sect.; the data prove unambiguously
that the dipropoxyphenyl group in the unsymmetrical com-
pound 4 is attached to C-3 of the 2-pyrazoline ring. The 1H
and 13C NMR spectroscopic data of the 1H-pyrazoles 6, 9,
11, 12 and 15 are summarized in Tables 1 and 2. In order to
demonstrate the possibilities given by the two-dimensional
measurements mentioned above, the complete correlation
of the 1H and 13C NMR signals with certain nuclei of com-
pound 9 is given in Figure 1; not only the two different
benzene rings but even the four slightly different propoxy
groups could be clearly discriminated.
Table 1. 13C NMR spectroscopic data of the compounds 9, 11, 12
and 15, δ values in CDCl3/C6D6 (1:1), TMS as internal standard
Compd.
Pyrazole rings
Benzene rings
Propoxy groups
1-CH3 C-3 HC-4 C-5 CH Cq
CqO OCH2 CH2 CH3
9
37.5
37.4
147.4 108.6 141.2 113.8 122.0 150.9 70.2
114.5 124.0 151.0 70.2
22.9 10.7
22.9 10.7
23.1 10.8
23.1 11.0
114.8
115.4
116.4
117.7
153.5 71.0
153.8 71.3
11
12
147.2 108.4 140.5 113.5 122.0 150.4 69.8
114.1 123.3 150.6 70.5
22.5 10.3
22.7 10.4
22.8 10.6
115.2
116.4
153.5 70.8
37.6
37.7
146.9 108.6 141.2 113.2 120.3 150.6 70.2
113.8 121.8 150.9 70.2
147.4 108.8 141.4 114.5 123.8 151.0 70.2
114.7 124.2 151.1 71.1
23.0 10.6
23.0 10.6
23.1 10.8
23.1 10.8
23.1 11.0
23.1 11.0
115.1
116.4
116.5
117.8
153.5 71.2
153.8 71.2
15
37.8
37.8
147.6 109.1 140.9 112.7 122.3 150.7 70.5
147.6 109.4 141.1 113.8 122.3 150.7 71.3
114.4 123.7 150.9 71.3
23.2 11.0
23.2 11.0
23.4 11.1
23.5 11.3
23.5 11.4
115.5 123.7 151.1 71.5
116.4
116.8
153.8 71.5
The UV spectra of the series 9, 11 and 15 with one, two
and four 1H-pyrazole rings, which are linked by 1,4-phenyl-
ene units, are shown in Figure 2. There is a small bathoch-
romic shift (dotted line) of the long-wavelength absorption
in the cross-conjugated oligomer series. A comparable result
was found for the oligochalcone series 7, 10 and 13.[4] The
conjugation in compounds 9, 11 and 15 is additionally di-
minished by the torsion of the ring planes. The convergence
Scheme 3. Transformation of chalcones 7, 10, 13 and 14 to the 1H-
pyrazoles 9, 11, 12, 15 and 16
of 16, which represents a chain of 13 rings in an alternate of the λmax values to a limiting value λϱ for increasing
sequence of benzene rings and 1H-pyrazole rings. length of the cross-conjugated array of ring systems seems
3374
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Eur. J. Org. Chem. 2003, 3372Ϫ3377

Oligo(1,4-phenylenepyrazole-3,5-diyl)s
FULL PAPER
kaline catalysis. The target compounds were characterized
by their 1H NMR, 13C NMR, mass and UV spectra. Cross-
conjugation in the ‘‘chain of rings’’ leads to a slight ba-
thochromic shift of the long-wavelength absorption with in-
creasing number of (hetero)aromatic rings.
Experimental Section
General: Melting points were determined with an SMP/3 apparatus
from Stuart Scientifique and are uncorrected. The 1H and 13C
NMR spectra were recorded with Bruker AC-200, AC-300, AMX-
400 and Avance 600 spectrometers; in order to obtain spectra with-
out many superimposed signals, a 1:1 mixture of CDCl3 and C6D6
was used as solvent, with TMS as internal standard. Mass spectra
were obtained with a Finnigan MAT-95 instrument with the field
desorption technique (FD) or with a Varian MAT-CH7A instru-
ment with the electron impact method (EI, 70 eV). UV/Vis spectra
were measured with a Zeiss MCS-320/340 spectrometer. Combus-
tion analyses were performed with the Elementar Vario EL3 appar-
atus in the Chemistry Department of the University of Mainz.
1
Figure 1. Correlation of the H chemical shifts (upper values) and
the 13C chemical shifts (lower values) of 9 with certain protons
and carbon atoms, respectively [measurement in C6D6/CDCl3 (1:1),
TMS as internal standard]
Starting Compounds
(E)-1-(2,5-Dipropoxyphenyl)-3-phenyl-2-propen-1-one (1): A solu-
tion of 2,5-dipropoxyacetophenone[2] (1.0 g, 4.2 mmol) and benzal-
dehyde (0.56 mL, 0.588 g, 5.5 mmol) in ethanol (6 mL) was treated
for 5 h with 1.5  KOH (2.0 mL). Stirring was continued at ambi-
ent temperature for 30 h. Column chromatography (44 ϫ 3 cm
SiO2, toluene/ethyl acetate, 40:1) yielded 820 mg (60%) of 1 as an
almost colorless oil. 1H NMR (CDCl3/C6D6, 1:1): δ ϭ 0.80 (t, 3
H, CH3), 0.88 (t, 3 H, CH3), 1.55 (m, 2 H, CH2), 1.62 (m, 2 H,
CH2), 3.64 (t, 2 H, OCH2), 3.68 (t, 2 H, OCH2), 6.63 (d, 1 H,
aromat. H, dipropoxyphenyl), 6.89 (dd, 1 H, aromat. H, dipropoxy-
phenyl), 7.13 (m, 3 H, aromat. H, phenyl), 7.28 (d, 1 H, aromat.
H, dipropoxyphenyl), 7.38 (m, 2 H, aromat. H, phenyl), 7.48 (d,
3J ϭ 15.6 Hz, 1 H, 2-H), 7.68 (3J ϭ 15.6 Hz, 1 H, 3-H) ppm. 13C
NMR (CDCl3/C6D6, 1:1): δ ϭ 10.3, 10.4 (CH3), 22.5, 22.6 (CH2),
69.9, 70.8 (OCH2), 114.3, 115.0, 120.0 (aromat. CH, dipropoxy-
phenyl), 127.2, 135.3 (aromat. Cq), 128.3, 128.9 (aromat. CH, phe-
nyl, partly superimposed), 129.9 (C-2), 142.2 (C-3), 152.1, 153.2
(aromat. CqO), 191.8 (C-1) ppm. FD MS: m/z (%) ϭ 324 (100)
[Mϩ]. C21H24O3 (324.4): calcd. C 77.75, H 7.46; found C 77.78,
H 7.28.
Figure 2. UV spectra of 9, 11 and 15 (from bottom to top) meas-
ured in chloroform and the bathochromic shift of the long-wave-
length absorption
The enones 7, 10, 13 and 14 were prepared according to literature
methods.[2,3]
to be slow; however, we did not attempt the calculation of
[4]
Preparation of 1H-Pyrazoles 6 and 9 via 2-Pyrazolines 4 and 8 in
the Protic Solvent Methanol: Methylhydrazine (2) (0.22 mL, 0.19 g,
4.13 mmol) in methanol (1.0 mL) was slowly added dropwise at
0 °C under argon to a solution of enone 1 (0.325 g, 1.0 mmol) in
dry methanol (20 mL). After about 15 min of stirring, 4 started to
precipitate from the light-yellow solution. TLC (SiO2, toluene/ethyl
acetate, 15:1) showed that the reaction had ended after about 1 h.
The precipitate of 4 was washed with n-hexane (10 mL) and recrys-
tallized from ethanol (yield 202 mg, 57%, m.p. 89 °C).
λϱ and the effective conjugation length nECL
,
because the
accuracy of the available spectrometer was Ϯ1 nm and the
increase of the λmax values in the series 9, 11, 15 is relatively
small (14 nm).
Conclusion
Cross-conjugated oligomers of alternating benzene and
1H-pyrazole rings can be obtained by reaction of the corre-
sponding chalcones with methylhydrazine and subsequent
oxidation with DDQ. Since monosubstituted hydrazines are
bifunctional nucleophiles and enones are bifunctional elec-
trophiles, four different primary steps are possible; never-
The analogous reaction of enone 7 and 2 is somewhat slower, so
the mixture was refluxed for 45 min. Column chromatography (35
ϫ 1.5 cm SiO2, toluene/ethyl acetate, 10:1) of the residue yielded
66% of 8, an oil which already contained some autoxidation prod-
uct 9. The regular oxidation of 4 and 8 was achieved in situ with
DDQ (5) (96 mg, 0.42 mmol) in boiling benzene (3.0 mL). After
theless, a regioselective cyclization reaction is feasible by al- 1 h, the raw products were purified by column chromatography (35
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H. Meier, A. Hormaza
FULL PAPER
ϫ 1.5 cm SiO2, toluene/ethyl acetate, 15:1); 6 could be obtained
from 1 in a yield of 74% and 9 in a yield of 78% (from 7).
The analogous reaction of 10 and 2 and the subsequent oxidation
with 5 led to a mixture of the bis(pyrazols) 11 and 12, which could
not be separated. According to the 1H NMR spectrum of the mix-
ture the ratio 11:12 amounts to 44:56.
rac-3-(2,5-Dipropoxyphenyl)-1-methyl-5-phenyl-4,5-dihydro-1H-
pyrazole (4) and 3-(2,5-Dipropoxyphenyl)-1-methyl-5-phenyl-1H-
pyrazole (6): The intermediate 2-pyrazoline rac-4 was characterized
by NMR spectroscopy and mass spectrometry; the raw product is
sufficiently pure for the subsequent oxidation with DDQ (5). 4: 1H
NMR (CDCl3/C6D6, 1:1): δ ϭ 0.79 (t, 3 H, CH3), 0.88 (t, 3 H,
CH3), 1.50 (m, 2 H, CH2), 1.63 (m, 2 H, CH2), 2.74 (s, 3 H, NCH3),
3.07 (dd, 2J ϭ Ϫ16.8, 3J ϭ 14.9 Hz, 1 H, 4-H), 3.57 (m, 2 H,
Preparation of 1H-Pyrazoles 6, 9, 11 and 15 in the Presence of
Alkali: Methylhydrazine (2) (4.0 mmol, 0.185 g per enone unit) was
slowly added to 1, 7, 10 or 13 (1.0 mmol) and KOH (1.5 g,
27 mmol) in ethanol (150 mL), under argon at room temperature.
After refluxing for 1.5 h, the reaction mixture was filtered and con-
centrated to dryness. The residue was dissolved in chloroform
(80 mL), washed with water (40 mL) and dried with Na2SO4. The
crude pyrazolines were oxidized in benzene (15 mL) with DDQ (5)
(0.3 g, 1.3 equiv. per pyrazoline ring). After refluxing for 1 h, the
mixture was filtered and the residue washed with toluene (10 mL).
The concentrated filtrate was subjected to column chromatography
(3 ϫ 44 cm SiO2, toluene/ethyl acetate, 5:1). The target compounds
6, 9, 11 and 15 could be obtained in yields of 68, 78, 38 and
12%, respectively.
3
OCH2), 3.61 (dd, 2J ϭ Ϫ16.8, J ϭ 9.8 Hz, 1 H, 4-H), 3.72 (t, 3
3
H, OCH2), 3.91 (dd, 3J ϭ 14.9, J ϭ 9.8 Hz, 1 H, 5-H), 6.58 (d,
3
3J ϭ 9.0 Hz, 1 H, 3-H, dipropoxyphenyl), 6.76 (dd, J ϭ 9.0, 4J ϭ
3.1 Hz, 4-H, dipropoxyphenyl), 7.12 (m, 1 H, 4-H, phenyl), 7.20
(m, 2 H, 3-H, 5-H, phenyl), 7.38 (m, 2 H, 2-H, 6-H, phenyl), 7.57
(d, 4J ϭ 3.1 Hz, 1 H, 6-H, dipropoxyphenyl) ppm. 13C NMR
(CDCl3/C6D6, 1:1): δ ϭ 10.7, 10.8 (CH3), 22.9, 23.0 (CH2), 41.8
(NCH3), 46.9 (C-4), 70.1, 70.7 (OCH2), 74.6 (C-5), 113.8, 114.1,
117.1 (C-3, C-4, C-6, dipropoxyphenyl), 123.4 (C-1, dipropoxy-
phenyl), 127.8, 128.8, 128.8 (C-2, C-3, C-4, C-5, C-6, phenyl), 141.2
(C-1, phenyl), 149.7 (C-3), 151.5, 153.5 (C-2, C-5, dipropoxy-
phenyl) ppm. EI MS (70 eV): m/z (%) ϭ 352 (100) [Mϩ], 309 (24),
275 (14). On standing in solution, the compound shows a dehydro-
genation to pyrazole 6, which is formed by oxidation of the raw
product 4 with DDQ (5); see above. Pyrazole 6 is a colorless solid
5,5-(2,5-Dipropoxy-1,4-phenylene)bis[3-(2,5-dipropoxyphenyl)-1-
methyl-1H-pyrazole] (11): Yield 38%, almost colorless solid, m.p.
153 °C.[22] UV (CHCl3): λmax ϭ 259 nm (ε ϭ 50520 cm2·mmolϪ1),
317 nm (ε ϭ 40220 cm2·mmolϪ1). FD MS: m/z (%) ϭ 739 (100)
[Mϩ]. C44H58N4O6 (738.9): calcd. C 71.52, H 7.91, N 7.58; found
C 71.53, H 8.02, N 7.41.
1
3-(2,5-Dipropoxyphenyl)-5-{4-[5-(2,5-dipropoxyphenyl)-1-methyl-
1H-pyrazol-3-yl]2,5-dipropoxyphenyl}-1-methyl-1H-pyrazole (12):
As discussed above, the reaction mixture 11/12 could not be sepa-
rated. Since 11 could be selectively formed by applying base cataly-
sis, the 1H and 13C NMR signals of 12, listed in Tables 1 and 2,
were obtained from the spectra of the mixture.
which melts at 75 °C. H NMR (CDCl3/C6D6, 1:1): δ ϭ 0.90 (t, 3
H, CH3), 0.91 (t, 3 H, CH3), 1.66 (m, 4 H, CH2), 3.64 (s, 3 H,
3
NCH3), 3.72 (t, 2 H, OCH2), 3.80 (t, 2 H, OCH2), 6.70 (d, J ϭ
9.3 Hz, 1 H, 3-H, dipropoxyphenyl), 6.77 (dd, 3J ϭ 9.3, 4J ϭ
2.6 Hz, 1 H, 4-H, dipropoxyphenyl), 7.01 (s, 1 H, 4-H), 7.18 (m, 3
H, m-H, p-H, phenyl), 7.28 (m, 2 H, o-H, phenyl), 7.81 (d, 4J ϭ
2.6 Hz, 1 H, 6-H, dipropoxyphenyl) ppm. 13C NMR (CDCl3/C6D6,
1:1): δ ϭ 10.4, 10.6 (CH3), 22.7, 22.8 (CH2), 37.1 (NCH3), 69.9,
70.6 (OCH2), 107.6 (C-4), 113.7, 114.1, 115.2 (aromat. CH, dipro-
poxyphenyl), 123.4, 150.6, 153.5 (aromat. Cq, dipropoxyphenyl),
128.0, 128.5, 128.6 (aromat. CH, phenyl), 131.2 (aromat. Cq, phe-
nyl), 143.8 (C-5), 147.4 (C-3) ppm. FD MS: m/z (%) ϭ 351 (100)
[M ϩ Hϩ]. C22H26N2O2 (350.48): calcd. C 75.40, H 7.48, N 7.99;
found C 75.39, H 7.51, N 7.99.
3,3Ј-(2,5-Dipropoxy-1,4-phenylene)bis(5-{4-[3-(2,5-dipropoxy-
phenyl)-1-methyl-1H-pyrazol-5-yl]-2,5-dipropoxyphenyl}-1-methyl-
1H-pyrazole) (15): Yield 12%, m.p. 192 °C.[22] UV (CHCl3): λmax ϭ
262 nm (ε
ϭ ϭ 65830
70460 cm2·mmolϪ1), 324 nm (ε
cm2·mmolϪ1). FD MS: m/z (%) ϭ 1282 (100 [Mϩ]. C76H98N8O10
(1282.7): calcd. C 71.11, H 7.70, N 8.73; found C 71.08, H 7.68,
N 8.75.
5,5Ј-(2,5-Dipropoxy-1,4-phenylene)bis{3-[4-(5-{4-[3-(2,5-dipropoxyl-
phenyl)-1-methyl-1H-pyrazol-5-yl]-2,5-dipropoxyphenyl}-1-methyl-
1H-pyrazol-3-yl)-2,5-dipropoxy-phenyl]-1-methyl-1H-pyrazole} (16):
The yield of the compound is so low that we did not attempt an
isolation and purification. The FD MS spectrum showed unam-
biguously the expected molecular ions at m/z (%) ϭ 1228 (100).
3,5-Bis(2,5-dipropoxyphenyl)-1-methyl-4,5-dihydro-1H-pyrazole (8)
and 3,5-Bis(2,5-dipropoxyphenyl)-1-methyl-1H-pyrazole (9): The in-
termediate 2-pyrazoline 8 was obtained in a yield of 66%; it is a
colorless oil. The compound, which is not stable in air, was charac-
terized by its 1H NMR, 13C NMR and mass spectra. 1H NMR
(CDCl3): δ ϭ 0.97 (t, 3 H, CH3), 1.00 (t, 6 H, CH3), 1.02 (t, 3 H,
CH3), 1.67Ϫ1.82 (m, 8 H, CH2), 2.81 (dd, 2J ϭ Ϫ16.6, 3J ϭ
14.6 Hz, 1 H, 4-H), 2.83 (s, 3 H, NCH3), 3.75Ϫ3.93 (m, 9 H, OCH2 Acknowledgments
3
3
and 4-H), 4.44 (dd, J ϭ 14.6, J ϭ 9.8 Hz, 1 H, 5-H), 6.70Ϫ6.85
(m, 4 H, aromat. H), 7.23 (m, 1 H, aromat. H), 7.35 (m, 1 H, aro-
mat. H) ppm. 13C NMR (CDCl3): δ ϭ 10.5, 10.5, 10.8, 10.8 (CH3),
22.7, 22.7, 22.7, 22.8 (CH2), 42.2 (NCH3), 44.7 (C-4), 67.5 (C-5),
70.2, 70.2, 70.3, 70.8 (OCH2), 112.5, 113.4, 113.8, 113.8, 113.9,
116.9 (aromat. CH), 130.6 (aromat. Cq), 149.1 (C-3), 151.1, 151.4,
153.1, 153.4 (aromat. CqO) ppm. FD MS: m/z (%) ϭ 468 (100)
[Mϩ]. On standing in solution, 8 shows a slow dehydrogenation to
pyrazole 9, which is formed by oxidation of the raw product 8 with
We are grateful to the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen Industrie for financial support. A. H.
thanks the DAAD for a stipend.
[1]
[1a]
See for example:
K. Müllen, G. Wegner, Electronic Materi-
[1b]
als: The Oligomer Approach; Wiley-VCH, Weinheim, 1998.
R. E. Martin, F. Diederich, Angew. Chem. 1999, 111,
[1c]
1440Ϫ1469; Angew. Chem. Int. Ed. 1999, 38, 1350Ϫ1377.
A. Kraft, A. C. Grimsdale, A. B. Holmes, Angew. Chem. 1998,
DDQ (5). Pyrazole 9 is a yellowish oil.[22] UV (CHCl3): λmax
ϭ
[1d]
110, 416Ϫ443; Angew. Chem. Int. Ed. 1998, 37, 403Ϫ428.
256 nm (ε
ϭ ϭ 13850
16420 cm2·mmolϪ1), 310 nm (ε
J. M. Tour, Adv. Mater. 1994, 6, 190Ϫ198.
H. Meier, H. Aust, J. Prakt. Chem. 1999, 341, 466Ϫ471.
H. Aust, D. Ickenroth, H. Meier, J. Prakt. Chem. 1999, 341,
523Ϫ528.
cm2·mmolϪ1). FD MS: m/z (%) ϭ 467 (100) [Mϩ]. C28H38N2O4
(466.6): calcd. C 72.07, H 8.21, N 6.00; found C 72.11, H 8.11,
N 6.00.
[2]
[3]
3376
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2003, 3372Ϫ3377

Oligo(1,4-phenylenepyrazole-3,5-diyl)s
FULL PAPER
H. Oleinek, I. Zugra˘vescu, Maromol. Chem. 1972, 157,
179Ϫ185.
G. Coispeau, J. Elguero, Bull. Soc. Chim. Fr. 1970, 2717Ϫ2736.
J. L. Aubagnac, J. Elguero, R. Jacquier, Bull. Soc. Chim. Fr.
1969, 3292Ϫ3299.
J. Elguero, R. Jacquier, C. Muratelle, Bull. Soc. Chim. Fr.
1968, 2506Ϫ2513.
A. Wagner, C.-W. Schellhammer, S. Petersen, Angew. Chem.
1966, 78, 769Ϫ774.
K. Morimoto, Y. Hayashi, A. Inami, Bull. Chem. Soc., Jpn.
1963, 36, 1651Ϫ1654.
C. G. A. Pinto, A. M. S. Silva, J. A. S. Cavaleiro, J. Elguero,
Eur. J. Org. Chem. 2003, 747Ϫ755.
[4]
[14]
H. Meier, H. Aust, D. Ickenroth, H. Kolshorn, J. Prakt. Chem.
1999, 341, 529Ϫ535.
[5]
[15]
[16]
H. Meier, A. Hormaza, J. Prakt. Chem. 2000, 342, 637Ϫ641.
[6]
A. R. Katritzky, C. W. Rees, E. F. Scriven, Comprehensive Het-
erocyclic Chemistry II, Pergamon, Oxford, 1996, vol. 2, 3, 5, 6
[17]
[18]
[19]
[20]
[21]
and 9.
[7]
See for example: J. Elguero, in Comprehensive Heterocyclic
Chemistry II (Eds.: A. R. Katritzky, C. W. Rees, E. F. Scriven),
Pergamon, Oxford, 1996, vol. 3, p. 1Ϫ75, and refs.[8Ϫ19]
N. Yoshihara, T. Hasegawa, S. Hasegawa, Bull. Chem. Soc. Jpn.
[8]
1991, 64, 719Ϫ720.
[9]
H. S. Patel, Eur. Polym. J. 1986, 22, 443Ϫ446.
[10]
D. Simon, O. Lafont, C. C. Farnoux, M. Miocque, J. Hetero-
cycl. Chem. 1985, 22, 1551Ϫ1557.
H. Meier in M. Hesse, H. Meier, B. Zeeh, Spektroskopische
Methoden in der organischen Chemie, 6th ed., Thieme,
Stuttgart, 2002, p. 72 ff.
[11]
N. El-Rayyes, A.-J. A. Al-Johary, J. Chem. Eng. Data 1985,
30, 500Ϫ502.
[12]
[22]
1
N. R. El-Rayyes, G. H. Hovakeemian, H. S. Hmoud, J. Chem.
The H and 13C NMR spectroscopic data are summarized in
Eng. Data 1984, 29, 225Ϫ229.
N. R. El-Rayyes, G. H. Hovakeemian, H. Hammoud, Org.
Tables 1 and 2. TMS as internal standard; the numbering
corresponds to the nomenclature.
[13]
Magn. Res. 1983, 21, 243Ϫ245.
Received April 8, 2003
Eur. J. Org. Chem. 2003, 3372Ϫ3377
www.eurjoc.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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