The preparation of 3- (2-phenylethenyl)-1H-pyrazoles from dilithiated (3E)-4-phenyl-3-buten-2-one hydrazones

Article abstract of DOI:10.1081/SCC-100000580

The phenyl-, carbomethoxy-, and carboethoxy-hydrazones of (3E)-4-phenyl-3-buten-2-one [benzalacetone] were treated with excess lithium diisopropylamide, and the resulting 1,4-dianions were condensed with several aromatic esters, followed by acid cyclizati

Full text of DOI:10.1081/SCC-100000580

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THE PREPARATION OF 3-(2-PHENYLETHENYL)-1H-
PYRAZOLES FROM DILITHIATED (3E)-4-PHENYL-3-
BUTEN-2-ONE HYDRAZONES
Stefan J. Pastine a , Wayne Kelley Jr. a , Jennifer J. Bear a , J. Nathan Templeton III a &
Charles F. Beam b
a Department of Chemistry and Biochemistry, College of Charleston, Charleston, South
Carolina, 29424, U.S.A.
b Department of Chemistry and Biochemistry, College of Charleston, Charleston, South
Carolina, 29424, U.S.A.
Version of record first published: 16 Aug 2006.
To cite this article: Stefan J. Pastine , Wayne Kelley Jr. , Jennifer J. Bear , J. Nathan Templeton III & Charles F. Beam
(2001): THE PREPARATION OF 3-(2-PHENYLETHENYL)-1H-PYRAZOLES FROM DILITHIATED (3E)-4-PHENYL-3-BUTEN-2-
ONE HYDRAZONES, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 31:4, 539-548
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SYNTHETIC COMMUNICATIONS, 31(4), 539–548 (2001)
THE PREPARATION OF
3-(2-PHENYLETHENYL)-1H-PYRAZOLES
FROM DILITHIATED
(3E)-4-PHENYL-3-BUTEN-2-ONE
HYDRAZONES
Stefan J. Pastine, Wayne Kelley, Jr., Jennifer J. Bear,
J. Nathan Templeton III, and Charles F. Beam∗
Department of Chemistry and Biochemistry, College of
Charleston, Charleston, South Carolina 29424
ABSTRACT
The phenyl-, carbomethoxy-, and carboethoxy-hydrazones
of (3E)-4-phenyl-3-buten-2-one [benzalacetone] were treated with
excess lithium diisopropylamide, and the resulting 1,4-dianions
were condensed with several aromatic esters, followed by acid
cyclization of C-acylated intermediates, to afford substituted
3-(2-phenylethenyl)-1H-pyrazoles [3-styryl-pyrazoles].
The preparation and uses of substituted 1H-pyrazoles and related materials
are well-documented with regard to their biological potential, their use in other
syntheses, and in numerous studies, including dye stuffs (1–7). A favored tra-
ditional preparation of these compounds involves the condensation/cyclization of
symmetricalorunsymmetricalβ-diketoneswithhydrazines. Thelatterβ-diketones
∗Corresponding author.
539
Copyright ꢀ 2001 by Marcel Dekker, Inc.
www.dekker.com
C

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PASTINE ET AL.
usually afford a mixture of isomeric pyrazoles that would require additional sep-
aration, normally by chromatographic techniques. Also, only a limited number
of unsymmetrical β-diketones are commercially available. Another well-known
synthesis is the regioselective preparation of unsymmetrical pyrazoles by the 1,3-
dipolar addition of nitrilimines to alkynes. This preparative method does not appear
to be readily adaptable to the preparation of 3-styryl-pyrazoles (1–7), which is the
focus of this report.
In a series of earlier investigations, we prepared unsymmetrical 3,5-disubsti-
tuted 1H-pyrazoles from a variety of C(α),N-hydrazones and aromatic esters
or anhydrides (8–19). For example, the C(α),N-phenylhydrazones or C(α),N-
carboalkoxy hydrazones of ketones, such as acetophenone, were dilithiated with
lithium diisopropylamide (LDA), and the resulting 1,4-dianion intermediates were
regioselectively condensed with a variety of substituted benzoate esters to af-
ford C-acylated intermediates that were not isolated, but cyclized immediately
with aqueous acid to give the targeted pyrazoles. In each instance, only one iso-
meric pyrazole resulted, because the atoms making up the five-membered pyrazole
ring were in place in the C-acylation intermediate prior to cyclization. While
many of these studies have involved the utilization of acetophenones and re-
lated carbonyl compounds for making hydrazones, fewer all aliphatic ketones,
and no examples of α,β-unsaturated ketones, such as benzalacetone, have been
used.
There are only a few reports concerning the preparations and uses of 3-styryl-
pyrazoles, and only 1,5-diphenyl-3-(2-phenylethenyl)-1H-pyrazole, 5, made in
this study, is known (20–24). It has been [a] prepared by the reaction of (β-
arylacryloyl)-oxiranes with phenylhydrazine, or [b] used in electric circuit boards
impregnated with a fluorescent brightener for optical examination, or [c] made
by oxidative dehydrogenation of 4,5-dihydro-1H-pyrazoles with cobalt(II) and
oxygen, or [d] used in electrochemical reduction reactions, or also [e] used in
effect of nonlinear photochemical transformations on light generation in allowed
transitions of complex organic molecules, and [f] made as a part of additional
oxidative studies using manganese dioxide.
During this investigation, several benzalacetone hydrazones 2a–c were de-
protonated with excess LDA, and the resulting dilithiated intermediates 3a–c were
condensed at the carbanion center with a variety of substituted benzoate esters,
such as methyl benzoate [for 5 and 9], methyl 4-tert-butylbenzoate [for 13], (lithi-
ated) methyl 4-hydroxybenzoate [for 8 and 11], methyl 4-methoxybenzoate [for 6,
10 and 12], or methyl 3,4,5-trimethoxybenzoate [for 7]. After acid cyclization of
4 with 3 N hydrochloric acid, the desired 3-styryl-pyrazoles 5–13 were isolated in
38–93% yield. Styryl-pyrazoles, 6–13, prepared in the current study, are new, and
the one that has been reported earlier (5), had excellent agreement when comparing
melting points [this study, mp 138◦–139◦C; lit. (24) mp 139◦C].

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3-(2-PHENYLETHENYL)-1H-PYRAZOLES PREPARATION
541
CH3
C
CH3
H
H2N-NH-Z
H
H
N
C
C
C
C
O
C
Z
N
C6H5
C6H5
H
H
1
2a, Z = C6H5
2b,
Z = COOCH3
LDA = Lithum Diisopropylamide
2c, Z = COOCH2CH3
O
C
xs LDA
R5
H
N
H2C
C
CH2Li
Li
R5COOCH3
H
H
N
C
C
C
C
N
Z
C
H
N
Z
C6H5
C6H5
H
4
3a-c
5. R5 = C6H5; Z = C6H5
H3O+, heat
6. R5 = 4-CH3OC6H4; Z = C6H5
7. R5 = 3, 4, 5-(CH3O)3C6H2; Z = C6H5
8. R5 = 4-HOC6H4; Z = C6H5
9. R5 = C6H5; Z = COOCH3
10. R5 = 4-CH3OC6H4; Z = COOCH3
11. R5 = 4-HOC6H4; Z = COOCH3
12. R5 = 4-CH3OC6H4; Z = COOCH2CH3
13. R5 = 4-(CH3)3CC6H4; Z = COOCH2CH3
R5
H
N
C
Z
C
H
N
C6H5
5-13
EXPERIMENTAL
Melting points were obtained with a Mel-Temp II melting point apparatus
in open capillary tubes and are uncorrected. Fourier Transform IR spectra were
obtained with a Nicolet Impact 410 FT-IR; paraffin oil mulls. Proton and 13C
NMR spectra were obtained with a Varian Associates Mercury Oxford 300 MHz
nuclear magnetic resonance spectrometer, and chemical shifts were recorded in
δ ppm downfield from an internal tetramethylsilane (TMS) standard. Combustion
analyses for C, H, and N were performed by Quantitative Technologies, Inc., P.O.
Box 470, Whitehouse, NJ 08888. The THF was distilled from sodium (benzophe-
none ketyl as an indicator of dryness) prior to use, and additional chemicals were
obtained from Aldrich Chemical Co.
Infrared spectra displayed alkene absorptions from 1639–1646 cm−1 in all
products 5–13 and a carboalkoxy carbonyl in products 9–13 from 1756–1763 cm−1

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PASTINE ET AL.
was noted. The phenolic OH absorptions in 8 and 11 were poorly defined and
1
recorded as shoulders in the region ca. 3200 cm−1. The H NMR spectra dis-
played pyrazole C4-H proton absorptions that were upfield and distinguishable
from aromatic protons, and recorded as singlets from δ 6.60–6.88 ppm. The con-
jugation of the styryl group with the heteroaromatic pyrazole ring placed the trans
styryl proton absorptions with the aromatic protons. By comparison, the styryl
protons in the new carboalkoxyhydrazone starting materials 2b–c, not having this
conjugation, were displayed as two well-defined doublets upfield from the phenyl
protons at δ 6.86 or 6.85 and 7.03 or 7.05 ppm. The phenolic protons were sharply
defined and noted at δ 9.77 ppm in 8 and δ 9.76 ppm in 11. Other routine proton
absorptions were recorded as expected. Carbon-13 NMR spectra for 5–13 gave the
expected number of carbon absorptions for each compound. The C-4 carbon ab-
sorptions of the pyrazole ring were assigned in an analogous fashion to the C4-H
of the proton resonance spectra, where the chemical shifts were noted between
δ 104.6–108.7 ppm, and they were upfield from the regular aromatic carbon and
vinyl carbon resonance absorptions.
This is a strong-base synthetic method, with a detailed experimental pro-
cedure, and it is a convenient method for the preparation of a particular 3-(2-
phenylethenyl)-1H-pyrazole. All of the spectral data are consistent with the struc-
tural assignments made for each compound 5–13. The yields of these products
may not be optimal, especially for a particular compound, but the current general
procedure readily affords multi-gram quantities of pure products resulting from
recrystallization from common solvents, which are in sufficient amounts for a
variety of uses. The experimental procedure is straightforward so that someone
not necessarily familiar with strong base procedures can be successful with the
reactions, and the experimental set-up is not elaborate.
General Procedure for Preparation of Benzalacetone
Hydrazones 2a–c
Benzalacetone phenylhydrazone 2a has been reported (25), and carbo-
methoxy- and carboethoxy-hydrazones 2b and 2c are new. These materials were
made by a 1:1 condensation of benzalacetone 1 with the substituted hydrazine fol-
lowing a minor modification of a documented procedure (26). In a typical reaction,
0.100 mole of 1 was mixed with 0.105 mole [5% excess] of methyl hydrazincar-
boxylate or ethyl hydrazincarboxylate, dissolved in 200 mL of methanol or ethanol.
Glacial acetic acid (1 mL) was added, and the solution was heated gently in a fume
hood using an open beaker or Erlenmeyer flask for approximately 45 min until the
volume was reduced to 100 mL. Upon cooling crystallization occurred, and the
mixture was filtered on a Buchner funnel. On occasion a few crystals of ice had
to be added to induce crystallization. Further reduction in volume of the original
filtrate usually afforded a second crop of product.

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543
[1-(2(E)-Phenylethenyl)ethylidene]-hydrazinecarboxylic Acid,
Methyl Ester or Benzalacetone Carbomethoxyhydrazone (2b)
This compound, 20.1 g (92% yield) mp 163◦–164◦C (methanol), was pre-
pared from the condensation of 1 and methyl hydrazincarboxylate. IR5: 3221,
1732, 1709, 1628 and 1587 cm−1; 1H NMR (CDCl3) δ 2.06 (s, 3H, CH3), 3.88 (s,
3H, OCH3), 6.86 (d, 1H, vinyl, J = 16.5 Hz), 7.03 (d, 1H, vinyl, J = 16.5 Hz),
and 7.24–7.47 ppm (m, 5 H, ArH); 13C NMR (CDCl3) δ 11.0, 53.4, 127.0, 128.5,
128.8, 128.9, 133.5, 136.2, and 149.8 ppm. Anal. calcd. for C12H14N2O2: C, 66.04;
H, 6.47; N, 12.82. Found: C, 65.99; H, 6.47; N, 12.87.
[1-(2(E)-Phenylethenyl)ethylidene]-hydrazinecarboxylic Acid,
Ethyl Ester or Benzalacetone Carboethoxyhydrazone (2c)
This compound, 15.1 g (65% yield) mp 154◦–155.5◦C (ethanol), was pre-
pared from the condensation of 1 and ethyl hydrazincarboxylate. IR: 3230, 1728,
1709, 1626 and 1579 cm−1; 1H NMR (CDCl3) δ 1.35 (t, 3H, CH3), 2.05 (s, 3H,
CH3), 4.33 (q, 2H, CH2), 6.85 (d, 1H, vinyl, J = 16.5 Hz), 7.05 (d, 1H, vinyl,
J = 16.5 Hz), and 7.23–7.47 ppm (m, 5 H, ArH); 13C NMR (CDCl3) δ 10.9, 14.8,
62.3, 126.9, 128.5, 128.8, 129.1, 133.0. Anal. calcd. for C13H16N2O2: C, 67.22;
H, 6.94: N, 12.06 Found: C, 67.11; H, 6.98; N, 12.03.
General Procedure for Preparation of
3-(2-Phenylethenyl)-1H-pyrazoles 5–13
[0.015 mol scale; hydrazone: LDA: ester- 1:3:1 for 5–7,9,10,12,13 and
1:4:1 (13) for 8 and 11]
In a typical reaction sequence, LDA [0.047 mol; 0.063 mol for 8 and 11] was
prepared by the addition of 30 mL [or 39 mL for 8 and 11] of 1.6 M n-butyllithium
[0.047 mol; 0.063 mol for 8 and 11] to a three-neck round-bottom flask (ca. 500
mL) equipped with a nitrogen inlet tube, a side-arm addition funnel (ca. 125 mL),
and a stir bar. The flask was cooled in an ice-water bath and 4.81 g (0.047 mol) [or
6.41 g (0.063 mol) for 8 and 11] of diisopropylamine, dissolved in 35–50 mL of
dry THF (0◦C, N2), was added from the addition funnel at a fast dropwise rate over
a period of 5 min. The solution was stirred for an additional 15–20 min and treated
via the addition funnel with 0.015 mol of benzalacetone, phenylhydrazone 2a, or
carbomethoxyhydrazone 2b, or carboethoxyhydrazone 2c dissoved in 50 mL of
THF. In order to speed up the solution process, the mixture of 2b was heated gently
before pouring it into the addition funnel. After 45–60 min (0◦C, N2), 0.0158 mol
of ester [5% excess] dissolved in 35–45 mL of THF, was added to the dilithiated
intermediate, and the solution was stirred for 45–60 min for 5 and 13, 1–1.5 h

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PASTINE ET AL.
for 6, 7, 10, and 12, and 2 h for 8 and 11 (0◦C, N2). Finally, 100 mL of 3 N HCl
was added, and the two-phase mixture was well-stirred and heated under reflux
for approximately 45–60 min. At the end of this period, the mixture was poured
into a large flask containing ice (ca. 100 g), followed by the addition of 100 mL
of solvent-grade ether. The mixture was then neutralized with solid sodium bicar-
bonate and the layers were separated. The aqueous layer was extracted with ether
or THF (2 × 75 mL), and the organic fractions were combined, evaporated, and
recrystallized.
1,5-Diphenyl-3-(2-phenylethenyl)-1H-pyrazole (5)
This compound, 3.90 g (81% yield) mp 138◦–139◦C (ethanol) [lit. (24) mp
139◦C], was prepared from 0.0150 mol of 3a and 0.0158 mol methyl benzoate. IR:
1646 cm−1; 1H NMR (CDCl3) δ 6.74 (s, 1H, C4-H), 7.16–7.39, and 7.52–7.55 ppm
(m, 17H, styryl and ArH); 13C NMR (CDCl3) δ 105.2, 120.7, 125.3, 126.7, 127.6,
127.9, 128.5, 128.7, 128.90, 128.92, 129.1, 130.6, 130.9, 137.3, 140.2, 144.4, and
151.4 ppm.
5-(4-Methoxyphenyl)-1-phenyl-3-(2-phenylethenyl)-1H-pyrazole 6
This compound, 4.15g (79% yield) mp 114◦–116◦C (ethanol), was prepared
from 0.0150 mol of 3a and 0.0158 mol methyl 4-methoxybenzoate. IR: 1645 cm−1
;
1H NMR (CDCl3) δ 3.77 (s, 3H, ArOCH3), 6.66 (s, 1H, C4-H), 6.79–6.84, and
7.11–7.53 ppm (m, 16H, styryl and ArH); 13C NMR (CDCl3) δ 55.4, 104.6, 114.1,
120.7, 122.9, 125.3, 126.6, 127.4, 127.9, 128.8, 129.0, 130.1, 130.7, 137.3, 140.2,
144.2, 151.2, and 159.7 ppm. Anal. calcd. for C24H20N2O: C, 81.79; H, 5.72; N,
7.95. Found: C, 81.71; H, 5.66; N, 7.86.
1-Phenyl-3-(2-phenylethenyl)-5-(3,4,5-trimethoxyphenyl)-1H-pyrazole (7)
This compound, 5.88 g (93% yield) mp 116◦–118◦C (ethanol), was prepared
from 0.0150 mol of 3a and 0.0158 mol methyl 3,4,5-trimethoxybenzoate. IR: 3628,
1
3546, 1646, and 1625 cm−1; H NMR (CDCl3) δ 3.67 (s, 6H, ArOCH3), 3.86
(s, 3H, ArOCH3), 6.43 (s, 2H, ArH), 6.74 (s, 1H, C4-H), 7.22–7.38, and 7.52–7.54
ppm (m, 12 H, styryl and ArH); 13C NMR (CDCl3) δ 56.2, 61.2, 104.6, 106.2,
120.6, 125.7, 125.8, 126.7, 127.8, 128.0, 128.9, 129.2, 131.0, 137.3, 138.3, 140.3,
144.4, 151.4, and 153.4 ppm. Anal. calcd. for C26H24N2O3·1/2H2O: C, 74.09; H,
5.97; N, 6.65. Found: C, 74.26; H, 6.30; N, 6.40.

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545
5-(4-Hydoxyphenyl)-1-phenyl-3-(2-phenylethenyl)-1H-pyrazole (8)
This compound, 3.88 g (77% yield) mp 250◦–252◦C (ethanol/toluene), was
preparedfrom0.0150molof3aand0.0158mollithiatedmethyl4-hydoxybenzoate.
IR: 3181 sh and 1646 cm−1; 1H NMR (DMSO-d6) δ 6.87 (s, 1H, C4-H), 6.73–6.77,
7.05–7.38, 7.58, and 7.59 ppm (m, 14H, styryl and ArH) and 9.77 (s, 1H, ArOH);
13C NMR (DMSO-d6) δ 104.6, 115.4, 120.5, 120.6, 124.9, 126.4, 127.4, 127.8,
128.8, 129.0, 129.9, 130.3, 136.8, 139.9, 144.0, 150.5, and 157.7 ppm. Anal. calcd.
for C23H18N2O: C, 81.63; H, 5.36; N, 8.28. Found: C, 81.27; H, 5.51; N, 8.21.
1-Carbomethoxy-5-phenyl-3-(2-phenylethenyl)-1H-pyrazole (9)
This compound, 2.22 g (49% yield) mp 120◦–121◦C (ethanol), was prepared
from 0.0150 mol of 3b and 0.0158 mol methyl benzoate. IR: 1762 and 1644 cm−1
;
1H NMR (CDCl3) δ 3.96 (s, 3H, OCH3). 6.65 (s, 1H, C4-H), and 7.14–7.53 ppm (m,
12H, styryl and ArH); 13C NMR (CDCl3) δ 54.9, 59.4, 108.8, 119.6, 127.0, 128.1,
128.7, 129.0, 129.2, 130.8, 134.4, 136.4, 148.4, 150.5, and 153.9 ppm. Anal. calcd.
for C13H16N2O2: C, 74.98; H, 5.30; N, 9.20. Found: C, 74.97; H, 5.22; N, 9.08.
1-Carbomethoxy-5-(4-methoxyphenyl-3-(2-phenylethenyl)-1H-pyrazole (10)
This compound, 2.96 g(59% yield) mp 165◦–167◦C (methanol), was pre-
pared from 0.0150 mol of 3b and 0.0158 mol methyl 4-methoxybenzoate. IR: 1758
and 1639 cm−1; 1H NMR (CDCl3) δ 3.84 (s, 3H, OCH3), 3.96 (s, 3H, OCH3), 6.60
(s, 1H, C4-H), 6.92–6.97, 7.13–7.40, and 7.48–7.52 ppm (m, 11H, styryl and ArH);
13C NMR (CDCl3) δ 54.9, 55.4, 108.4, 113.5, 119.7, 122.9, 126.9, 128.6, 128.9,
130.6, 134.2, 136.4, 148.3, 150.6, and 160.3 ppm. Anal. calcd. for C20H18N2O3:
C, 71.84; H, 5.43; N, 8.38. Found: C, 71.98; H, 5.41, 8.26.
1-Carbomethoxy-5-(4-hydoxyphenyl-3-(2-phenylethenyl)-1H-pyrazole (11)
This compound, 2.46 g (51% yield) mp 192◦–194◦C (ethanol), was prepared
from 0.0150 mol of 3b and 0.0158 mol lithiated methyl 4-hydroxybenzoate. IR:
3202 sh., 1756 and 1646 cm−1; 1H NMR (DMSO-d6) δ 3.83 (s, 3H, OCH3), 6.88
(s, 1H, C4-H), 6.79–6.81, 7.15–7.39, 7.53–7.62 (m, 11H, styryl and ArH) and 9.76
ppm (s, 1H, ArOH); 13C NMR (DMSO-d6) δ 54.3, 108.1, 114.7, 119.4, 120.9,
126.8, 128.4, 128.8, 130.4, 133.7, 136.2, 147.7, 150.1, 152.9, and 158.0 ppm.
Anal. calcd. for C19H16N2O3: C, 71.24; H, 5.03; N, 8.74. Found: C, 70.93; H,
5.21; N, 8.58.

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1-Carboethoxy-5-(4-methoxyphenyl-3-(2-phenylethenyl)-1H-pyrazole (12)
This compound, 2.55 g (49% yield) mp 162◦–163◦C (ethanol), was prepared
from 0.0150 mol of 3c and 0.0158 mol methyl 4-methoxybenzoate. IR: 1763 and
1639 cm−1; 1H NMR (CDCl3) δ 1.35 (t, 3H, CH3), 3.85 (s, 3H, OCH3), 4.42 (q,
2H, OCH2), 6.60 (s, 1H, C4-H), 6.92–6.97, 7.13–7.40, and 7.48–7.52 ppm (m,
11H, styryl and ArH); 13C NMR (CDCl3) δ 55.5, 64.5, 108.4, 113.5, 119.9, 123.3,
126.9, 128.6, 129.0, 130.6, 134.1, 136.5, 148.2, 150.1, 153.7, and 160.3 ppm. Anal.
calcd. for C21H20N2O3: C, 72.40; H, 5.79; N, 8.04. Found: C, 72.32; H, 5.80; N,
7.99.
1-Carboethoxy-5-(4-(1,1-dimethylethyl)-phenyl)-3-(2-phenylethenyl)-
1H-pyrazole (13)
This compound, 2.13 g (38% yield) mp 128◦–129◦C (ethanol), was prepared
from 0.0150 mol of 3c and 0.0158 mol methyl 4-tert-butylbenzoate. IR: 1763 and
1646 cm−1; 1H NMR (CDCl3) δ 1.32 (t, 3H, CH3), 1.36 (s, 9H, C(CH3)3), 4.41
(q, 2H, OCH2), 6.63 (s, 1H, C4-H), and 7.13–7.53 ppm (m, 11H, styryl and ArH);
13C NMR (CDCl3) δ 14.3, 31.5, 35.0, 64.5, 108.7, 120.0, 125.0, 127.0, 128.1,
128.7, 129.0, 134.12, 136.6, 148.4, 150.1, 152.3, and 153.8 ppm. Anal. calcd. for
C24H26N2O2: C, 76.98; H, 7.00; N, 7.48. Found: C, 76.79; H 7.10; N, 7.44.
ACKNOWLEDGMENTS
We thank the National Science Foundation’s Research in Undergraduate
Institutions through grant # 9708014, along with the Donors of the Petroleum
Research Fund, administered by the American Chemical Society, for support. The
acquisition of the 300 MHz NMR spectrometer was made possible through the
National Science Foundation’s Division of Undergraduate Education grant DUE
# 9750721.
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2. Kashima, C.; Harada, H.; Kita, I.; Fukuchi, I.; Hosomi, A. Synthesis 1994,
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Received in the USA May 10, 2000

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