Reaction of hydrazones derived from active methylene compounds with Vilsmeier-Haack reagent

Article abstract of DOI:10.1007/s00706-014-1293-7

Reaction of hydrazones derived from active methylene compounds with the Vilsmeier-Haack reagent was studied. Compounds with sulfone, ester, nitrile, triphenylphosphonium, and phthalimide moieties were evaluated. It was found that electron-withdrawing and

Full text of DOI:10.1007/s00706-014-1293-7

Monatsh Chem
DOI 10.1007/s00706-014-1293-7
ORIGINAL PAPER
Reaction of hydrazones derived from active methylene compounds
with Vilsmeier–Haack reagent
•
Sergey P. Ivonin Bohdan B. Kurpil’
•
•
Oleksandr O. Grygorenko Dmitry M. Volochnyuk
Received: 19 June 2014 / Accepted: 5 August 2014
Ó Springer-Verlag Wien 2014
Abstract Reaction of hydrazones derived from active
methylene compounds with the Vilsmeier–Haack reagent
was studied. Compounds with sulfone, ester, nitrile, tri-
phenylphosphonium, and phthalimide moieties were
evaluated. It was found that electron-withdrawing and
steric effects provided by the substituent at a position
strongly influenced the regioselectivity of the reaction.
Increasing mesomeric electron-withdrawing effect of this
group favors the formation of functionalized 1,3,4-trisub-
stituted pyrazoles as compared to 1,3-disubstituted
pyrazole-4-carbaldehydes. On the contrary, enhanced steric
hindrance and lowered electron-withdrawing effect shift
the balance toward 1,3-disubstituted pyrazole-4-carbalde-
hydes. Other factors such as substituent at the nitrogen
atom of the hydrazone, as well as reagent ratio, can affect
the outcome of the reaction dramatically, so that in certain
cases acyclic products are obtained.
importance for drug discovery and many other areas. The
classical [3 ? 2] approach to the pyrazole synthesis relying
on the use of CCC bis-electrophile and NN binucleophile as
the starting building blocks (Scheme 1) [1–3] is widely
used, but often leads to mixtures of regioisomers in the
case of non-symmetric polysubstituted pyrazoles. A pos-
sible alternative approach to the pyrazoles relies on [4 ? 1]
disconnection, which corresponds to the reaction of CCNN
binucleophile (e.g., hydrazone of an enolizable ketone 1)
with C-1 electrophilic building block (e.g., under Vilsme-
ier–Haack conditions (DMF–POCl3)). Reaction of
hydrazones with Vilsmeier–Haack reagent was widely used
for the preparation of 1,3,4-trisubstituted pyrazoles 2 or 3
starting from N-aryl hydrazones [4–12]; recently, we have
extended it to the corresponding N-alkyl derivatives
(Scheme 2) [13, 14]. Since in many cases the procedure led
to the formation of pyrazoles lacking any functional group
for further possible modification, in the current work we
have turned our attention to the reaction of Vilsmeier–
Haack reagent with hydrazones 4 bearing an additional
functional moiety at a position, i.e., those derived from
active methylene compounds. It should be noted that to
date, only N-arylhydrazones 5 and 6 were studied in the
reaction with DMF–POCl3; at these conditions, trisubsti-
tuted pyrazoles of type 3 were formed [15–20].
Keywords Heterocycles ꢀ Pyrazoles ꢀ Regioselectivity ꢀ
Electrophilic substitutions ꢀ Tautomerism
Introduction
Regioselective synthesis of non-symmetric polysubstituted
pyrazoles with aliphatic substituents is an important and
challenging task in heterocyclic chemistry, in view of their
In this work, we have studied the reaction of Vilsmeier–
Haack reagent with hydrazones 4a–4i bearing electron-
withdrawing group at the a position (Fig. 1) as a potential
method for the preparation of functionalized pyrazoles.
O. O. Grygorenko (&)
National Taras Shevchenko University of Kyiv, Volodymyrska
Street, 64, Kiev 01601, Ukraine
e-mail: gregor@univ.kiev.ua
Results and discussion
S. P. Ivonin ꢀ B. B. Kurpil’ ꢀ D. M. Volochnyuk
The main feature of the compounds of general formula 4
(as compared to their simple alkyl- or aryl-substituted
Institute of Organic Chemistry, National Academy of Sciences
of Ukraine, Murmanska Street 5, Kiev 02660, Ukraine
123

S. P. Ivonin et al.
Table 1 Reactions of hydrazones 4a–4e with Vilsmeier–Haack
reagent
Scheme 1
Scheme 2
No.
Hydrazone
R2
EWG
Products (yield/%)
1
2
3
4
5
4a
4b
4c
4d
4e
Me
Ph
Ts
9a (20), 10a (45)
9b (62), 10b (14)
9c (64)
Ts
Ph
COOEt
N-phtalimidyl
N-phtalimidyl
Me
Ph
10d (92)
10e (95)
Based on the thermodynamic stabilization of the tau-
tomers 7 over 8, one might expect preferential attack of the
Vilsmeier–Haack reagent at the a-CH2 unit of the sub-
strates 4a–4i, leading to the selective formation of
pyrazoles 9. On the contrary, the tautomers 8 are more
reactive toward electrophilic attack as compared to 8,
which can lead to the predominant formation of aldehydes
10 under kinetically controlled conditions. It was found
that sulfone-containing hydrazone 4a gave ca. 1:2 mixture
of pyrazoles 9a (20 %) and 10a (45 %) in the reaction with
an excess of Vilsmeier–Haack reagent (Table 1). Under
analogous conditions, hydrazone 4b gave pyrazoles 9b
(major, 62 %) and 10a (minor, 14 %). It should be noted
that we could not observe the corresponding aldehydes 10a
and 10b when the formylating agent was used at a 1:1 ratio;
only pyrazoles 9a and 9b were formed in low yields in this
case. These results show that tautomers of type 8, although
less stable as compared to 7, are still important in the case
of sulfone-substituted hydrazones 4a and 4b. On the other
hand, decreasing electron density at the NHR2 atom of the
hydrazone moiety due to conjugation suppresses formation
Fig. 1 Hydrazones 4a–4i studied in this work
counterparts) is stabilization of the enhydrazine tautomers
7. In the case of hydrazones derived from the aliphatic
ketones, this leads to preferential formation of 7 over an
alternative tautomer 8 (Table 1) [21]. These features
should strongly influence regioselectivity in the reaction of
4 with electrophilic reagents.
123

Reaction of hydrazones derived from active methylene compounds
Scheme 3
of the tautomers 8, which diminishes the yield of the
product of the formal attack of the electrophile at the a0-
CH3 group.
hydrolysis of 14h led to the formation of N-formylhyd-
razone 15 (72 %).
The reaction of hydrazone 4i with the Vilsmeier–Haack
reagent at a 1:1 ratio followed by a workup resulted in the
formation of pyrazole 9i (64 %) (Scheme 5). When 2.2-fold
excess of the reagent was used, acyclic product 14i was
obtained in 62 % yield. Notably, neither 4h nor 4i gave the
products of formal electrophilic attack at a0-CH3 moiety, which
can be explained by a too low content of tautomers, 8h and 8i.
Reaction of hydrazone 4c with the Vilsmeier–Haack
reagent led to the formation of pyrazole 9c (64 %). This
result is in accordance with the literature data for hydrazones
6 [17–20]. The observed decrease in the tendency of elec-
trophilic attack at the a0-CH3 group in the case of hydrazone
4c as compared to 4a and 4b can be explained by larger
electron-withdrawing effect of COOEt group as compared to
SO2Ph, which further shifts the equilibria 7c ¡ 8c toward 7c.
In the case of hydrazones 4d and 4e having a phthali-
mide moiety, aldehydes 10d (92 %) and 10e (95 %) were
the only products isolated. This result can be explained by
either lowered electron-withdrawing or increased steric
effect of the phthalimide fragment, which prevents the
attack at the a-CH2 unit.
Reaction of phosphorus-containing hydrazones 4f and
4g with the Vilsmeier–Haack reagent presumably resulted
in an initial attack at the N-2 atom of the hydrazone moiety.
After working up of the reaction mixture obtained from 4g,
the corresponding product 11g, as well as the product of its
further hydrolysis, 12, were isolated in 34 and 36 % yields,
respectively (Scheme 3); no traces of pyrazoles 9 or 10
were detected. In the case of 4f, only the product 12 was
isolated as the perchlorate (96 % yield). These results show
that positive charge at PPh?3 group prevents attack at both
a-and a0-carbon atoms of the starting material.
Conclusions
The regioselectivity in the reactions of hydrazones derived
from active methylene compounds having an a0-CH3 sub-
stituent (4a–4i) with the Vilsmeier–Haack reagent is
governed by a subtle balance between thermodynamic and
kinetic factors. The reaction can be discussed in relation with
hydrazone–enhydrazine tautomerism of the starting mate-
rial. In particular, both enhydrazine forms obtained by
prototropic migration from either a-CH2 or a0-CH3 moiety of
the hydrazone (7 and 9, respectively) can react with the
Vilsmeier–Haack reagent. Whereas tautomers of the type 7
are thermodynamically more stable and are formed pre-
dominantly, electrophilic attack at 8 is kinetically favorable
due to higher C-nucleophilicity. As a result, increasing
electon-withdrawing effect of the substituent at a position
diminishes the yield of the products resulting from formal
electrophilic attack at the a0-CH3 group, so that trisubstituted
functionalized pyrazoles 9 are obtained predominantly.1
Decreasing electron density at the NHR2 atom of the
Reaction of the cyano-substituted hydrazone 4h (which
exists as enhydrazine tautomer 7h) with Vilsmeier–Haack
reagent at 1:1 ratio followed by workup led to the forma-
tion of enamino nitrile 13h in 68 % yield (Scheme 4).
Surprisingly, compound 13h was not transformed to 9h and
remained intact even at prolonged heating in acidic media
(conc. HCl). The enhanced stability of 13h toward hydro-
lysis can be explained by effective conjugation. When 2.2-
fold excess of the reagent was used, the product of double
formylation 14h was isolated in 75 % yield. Alkaline
1
In addition to compounds 8a–8i, we have also attempted to study
hydrazones of general formula 8 with R2 = Ph, EWG = C(O)Me
(8j), CONMe2 (8k), and NO2 (8l). We could not obtain hydrazone 8j
due to its fast cyclization into the pyrazole derivative. Although
hydrazone 8k was formed, its purification failed in our hands.
Compound 8l was obtained, but it gave a complex mixture of
unidentified products upon reaction with Vilsmeier–Haack reagent.
123

S. P. Ivonin et al.
Scheme 4
Scheme 5
hydrazone moiety due to conjugation (i.e., when going from
R2 = Me to Ph) seems to give a similar effect. If a positively
charged electon-withdrawing group is present at the a
position, the initial attack of the electrophile occurs at the
NHR2 moiety of the hydrazone. Other factors such as reagent
ratio also have a strong impact on the reaction outcome, so
that in certain cases acyclic products are isolated.
prepared using the reported procedures. All other starting
materials were purchased from commercial sources. Ana-
lytical TLC was performed using Polychrom SI F254
plates. Column chromatography was performed using
Kieselgel Merck 60 (230–400 mesh) as the stationary
phase. 1H and 13C NMR spectra were recorded on a Bruker
Avance spectrometer (at 300 MHz for protons and 75 MHz
for carbon). Chemical shifts are reported in ppm downfield
from TMS (1H, 13C) as an internal standard. Elemental
analyses (C, H, N, S) were conducted at the Laboratory of
Organic Analysis, Institute of Organic Chemistry, National
Academy of Sciences of Ukraine; their results were found
to be in good agreement ( 0.3 %) with the calculated
values. Mass spectra were recorded on an Agilent 1100
LCMSD SL instrument (chemical ionization (APCI)).
Experimental
The solvents were purified according to the standard pro-
cedures. 1-Tosylpropan-2-one [22], 2-(2-oxopropyl)-2,3-
dihydro-1H-isoindole-1,3-dione [23], and hydrazones 4b
[24], 4c [25], 4e [26, 27], 4f [28], 4g [29], and 4i [30] were
123

Reaction of hydrazones derived from active methylene compounds
General procedure for the preparation of hydrazones
1-Methyl-3-[(toluene-4-sulfonyl)methyl]-1H-pyrazole-4-
carbaldehyde (10a, C13H14N2O3S)
4a, 4d, and 7h
Yield 45 %; pale yellow crystals; m.p.: 74–75 °C; MS
(CI): m/z = 279 (MH?); 1H NMR (300 MHz, CDCl3):
d = 9.68 (s, 1H), 7.84 (s, 1H), 7.68 (d, J = 8.4 Hz, 2H),
7.29 (d, J = 8.4 Hz, 2H), 4.71 (s, 2H), 3.92 (s, 3H), 2.43 (s,
3H) ppm; 13C NMR (75 MHz, DMSO-d6): d = 183.2,
144.9, 141.2, 135.6, 135.4, 129.6, 128.5, 122.7, 54.5, 39.7,
21.6 ppm.
A mixture of the corresponding ketone (0.1 mol) and
methylhydrazine (0.1 mol) in 100 cm3 MeOH was stirred
at 50 °C for 1 h. Then the mixture was cooled, the
precipitate was filtered, and dried on air to give the
product 4d or 7h. In the case of 4a, the mixture was
evaporated and used in the next step without analysis and
purification.
3-Methyl-1-phenyl-4-(toluene-4-sulfonyl)-1H-pyrazol
(9b, C17H16N2O2S)
2-[2-(2-Methylhydrazono)propyl]isoindoline-1,3-dione
(4d, C12H13N3O2)
Yield 62 %; pale yellow crystals; m.p.: 105–106 °C; MS
(CI): m/z = 313 (MH?); 1H NMR (300 MHz, CDCl3):
d = 8.37 (s, 1H), 7.86 (d, J = 8.4 Hz, 2H), 7.63 (d,
J = 8.4 Hz, 2H), 7.46 (t, J = 8.4 Hz, 2H), 7.34 (m, 3H),
2.42 (s, 3H), 2.41 (s, 3H) ppm; 13C NMR (75 MHz,
CDCl3): d = 149.0, 144.1, 139.3, 138.8, 130.5, 129.8,
129.6, 127.7, 127.1, 123.8, 119.4, 21.5, 12.4 ppm.
Compound 4d was prepared from 2-(2-oxopropyl)-2,3-
dihydro-1H-isoindole-1,3-dione. Yield 82 %; white crys-
1
tals; m.p.: 138–139 °C; MS (CI): m/z = 232 (MH?); H
NMR (300 MHz, CDCl3): d = 7.87–7.84 (m, 2H),
7.73–7.70 (m, 2H), 4.37 (s, 2H), 2.85 (s, 3H), 1.72 (s,
3H) ppm; 13C NMR (75 MHz, DMSO-d6): d = 168.1,
138.9, 134.9, 132.1, 123.5, 43.5, 38.0, 13.4 ppm.
1-Phenyl-3-[(toluene-4-sulfonyl)methyl]-1H-pyrazole-4-
carbaldehyde (10b, C18H16N2O3S)
3-(2-Methylhydrazinyl)but-2-enenitrile (7h, C5H9N3)
Compound 7h was prepared from a-cyanoacetone. Yield
78 %; yellowish crystals; m.p.: 82–83 °C; MS (CI):
m/z = 112 (MH?); 1H NMR (300 MHz, DMSO-d6):
d = 12.47 (br s, 1H), 6.18 (s, 1H), 2.39 (s, 3H), 2.21 (s,
3H) ppm; 13C NMR (75 MHz, DMSO-d6): d = 147.7,
145.4, 88.3, 34.1, 14.2 ppm.
Yield 14 %; yellowish crystals; m.p.: 127–129 °C; MS
1
(CI): m/z = 343 (MH?); H NMR (300 MHz, DMSO-d6):
d = 9.83 (s, 1H), 9.15 (s, 1H), 7.73 (d, J = 7.8 Hz, 2H),
7.65 (d, J = 8.4 Hz, 2H), 7.52 (t, J = 7.8 Hz, 2H), 7.41
(m, 3H), 5.06 (s, 2H), 2.39 (s, 3H) ppm; 13C NMR
(75 MHz, DMSO-d6): d = 185.6, 145.1, 143.4, 138.8,
135.9, 133.0, 130.1, 128.7, 128.3, 124.1, 119.6, 93.0, 53.9,
21.5 ppm.
General procedure for the reaction of hydrazones 4
with Vilsmeier–Haack reagent
3-Methyl-1-phenyl-1H-pyrazole-4-carboxylic acid ethyl
ester (9c, C13H14N2O2)
POCl3 (0.1 mol) was added dropwise to 20 cm3 DMF at
0 °C. After 1 h, a solution of hydrazone (0.05 mol) in
10 cm3 DMF was added dropwise at 0 °C. The mixture
was stirred at 0 °C for 1 h and at 80 °C for 1 h, then cooled
to ambient temperature and poured onto 100 g ice. The
precipitate formed was filtered to give the product 9a–9c,
9i, 10d, or 10e. The filtrate was made alkaline with 30 %
Yield 64 %; white crystals; m.p.: 55–56 °C; MS (CI):
m/z = 231 (MH?); 1H NMR (300 MHz, CDCl3): d = 8.33
(s, 1H), 7.66 (d, J = 8.0 Hz, 2H), 7.44 (t, J = 8.0 Hz, 2H),
7.30 (t, J = 7.6 Hz, 1H), 4.31 (q, J = 7.2 Hz, 2H), 2.55 (s,
3H), 1.36 (t, J = 7.2 Hz, 3H) ppm; 13C NMR (75 MHz,
DMSO-d6): d = 163.1, 151.5, 139.2, 132.3, 129.9, 127.3,
119.1, 114.0, 60.1, 14.7, 13.8 ppm.
aq. NaOH to pH
8 and extracted with CHCl3
3-(1,3-Dioxo-1,3-dihydroisoindol-2-ylmethyl)-1-methyl-
1H-pyrazole-4-carbaldehyde (10d, C14H11N3O3)
Yield 92 %; white crystals; m.p.: 230–231 °C; MS (CI):
m/z = 270 (MH?); 1H NMR (300 MHz, DMSO-d6):
d = 9.88 (s, 1H), 8.41 (s, 1H), 7.93–7.85 (m, 4H), 4.97
(s, 2H), 3.76 (s, 3H) ppm; 13C NMR (75 MHz, DMSO-d6):
d = 185.3, 167.8, 148.1, 138.5, 135.0, 132.1, 123.7, 120.5,
93.1, 35.2 ppm.
(3 9 200 cm3). The combined organic extracts were sep-
arated and dried over Na2SO4. The solvent was removed
under reduced pressure to give the product 10a, 10b, 11g,
14h, or 14i.
1,3-Dimethyl-4-(toluene-4-sulfonyl)-1H-pyrazole
(9a, C12H14N2O2S)
Yield 20 %; orange crystals; m.p.: 133–134 °C; MS (CI):
m/z = 251 (MH?); 1H NMR (300 MHz, CDCl3): d = 7.82
(s, 1H), 7.79 (d, J = 8.4 Hz, 2H), 7.29 (d, J = 8.4 Hz,
2H), 3.82 (s, 3H), 2.40 (s, 3H), 2.30 (s, 3H) ppm; 13C NMR
(75 MHz, CDCl3): d = 148.0, 143.8, 139.7, 133.8, 129.7,
126.9, 121.6, 39.2, 21.5, 12.2 ppm.
3-(1,3-Dioxo-1,3-dihydroisoindol-2-ylmethyl)-1-phenyl-
1H-pyrazole-4-carbaldehyde (10e, C19H13N3O3)
Yield 95 %; gray crystals; m.p.: 179–181 °C; MS (CI):
m/z = 332 (MH?); 1H NMR (300 MHz, DMSO-d6):
d = 10.00 (s, 1H), 9.23 (s, 1H), 7.92-7.89 (m, 4H), 7.72
123

S. P. Ivonin et al.
(d, J = 7.5 Hz, 2H), 7.48 (t, J = 7.5 Hz, 2H), 7.35 (t,
J = 8.1 Hz, 1H), 5.09 (s, 2H) ppm; 13C NMR (75 MHz,
DMSO-d6): d = 185.5, 167.9, 149.6, 138.9, 135.4, 135.1,
132.0, 130.1, 128.0, 123.8, 122.3, 119.5, 35.3 ppm.
DMSO-d6): d = 153.0, 138.9, 134.8, 130.1, 128.0, 119.4,
114.2, 93.5, 12.6 ppm.
2-[(Dimethylamino)methylene]-3-(methylhydrazono)
butyronitrile (13h, C8H14N4)
(2-Oxopropyl)triphenylphosphonium perchlorate
POCl3 (0.05 mol) was added dropwise to 10 cm3 DMF at
0 °C. After 1 h, a solution of hydrazone (0.05 mol) in
10 cm3 DMF was added dropwise at 0 °C. The mixture
was stirred at 0 °C for 0.5 h, and the precipitate formed
was filtered off. The filtrate was diluted with 100 cm3
water and made alkaline with 30 % aq. NaOH to pH 9. The
product was extracted with CHCl3 (3 9 100 cm3). The
combined organic extracts were separated and dried over
Na2SO4. The solvent was removed under reduced pressure
to give 13h. Yield 68 %; orange oil; MS (CI): m/z = 167
(12ꢀClO4, C21H20ClO5P)
POCl3 (0.1 mol) was added dropwise to 20 cm3 DMF at
0 °C. After 1 h a solution of hydrazone (0.05 mol) in
10 cm3 DMF was added dropwise at 0 °C. The mixture
was stirred at 0 °C for 1 h and at 80 °C for 1 h, then cooled
to ambient temperature, and HClO4 (0.05 mol) was added.
The precipitate was obtained and separated from reaction
mixture by filtration. Yield 96 %; white crystals; m.p.: ca.
1
70 °C; MS (CI): m/z = 321 (MH?); H NMR (300 MHz,
1
DMSO-d6): d = 7.78–7.73 (m, 15H), 7.75–7.72 (m, 6H),
5.53 (d, J = 11.7 Hz, 2H), 2.34 (s, 3H) ppm.
(MH?); H NMR (300 MHz, CDCl3): d = 7.65 (s, 1H),
5.47 (s, 1H), 3.65 (s, 3H), 2.99 (s, 6H), 2.17 (s, 3H) ppm;
13C NMR (75 MHz, DMSO-d6): d = 155.1, 151.6, 145.5,
88.6, 39.9, 34.1, 33.6, 14.4 ppm.
[2-(2-Formyl-2-phenylhydrazono)propyl]-
triphenylphosphonium chloride (11g, C28H26ClN2OP)
Yield 34 %; pale yellow crystals; m.p.: 165–166 °C; MS
N0-(1-Cyanoprop-2-ylidene)-N-methylformohydrazide
(15, C6H9N3O)
1
(CI): m/z = 438 (MH?); H NMR (300 MHz, DMSO-d6):
To a solution of 14h (10 mmol) in 50 cm3 MeOH, KOH
(30 mmol) was added. The resulting solution was refluxed
for 3 h, then cooled to room temperature and evaporated.
The residue was triturated with H2O to give the solid
product. Yield 72 %; pale yellow crystals; m.p.: 92–93 °C;
MS (CI): m/z = 140 (MH?); 1H NMR (300 MHz, DMSO-
d6): d = 9.52 (s, 1H), 6.70 (s, 2H), 3.45 (s, 3H), 2.18 (s,
3H) ppm; 13C NMR (75 MHz, DMSO-d6): d = 182.6,
148.4, 104.9, 33.8, 12.2 ppm.
d = 9.20 (s, 1H), 7.87–7.80 (m, 9H), 7.75–7.72 (m, 6H),
6.91 (t, J = 7.5 Hz, 2H), 6.59 (t, J = 7.2 Hz, 1H), 6.32 (d,
J = 7.8 Hz, 2H), 5.03 (d, J = 14.4 Hz, 2H), 1.99 (s, 3H)
ppm.
N0-[3-Cyano-4-(dimethylamino)but-3-en-2-ylidene]-N-
methylformohydrazide (14h, C9H14N4O)
Yield 75 %; orange crystals; m.p.: 55–57 °C; MS (CI):
m/z = 195 (MH?); 1H NMR (300 MHz, CDCl3): d = 9.56
(s, 1H), 8.74 (s, 1H), 3.61 (s, 3H), 3.10 (s, 3H), 3.04 (s,
3H), 2.36 (s, 3H) ppm; 13C NMR (75 MHz, DMSO-d6):
d = 183.2, 158.3, 154.7, 149.5, 93.1, 40.5, 34.3, 33.9,
13.7 ppm.
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Yield 62 %; yellow crystals; m.p.: 76–77 °C; MS (CI):
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3-Methyl-1-phenyl-1H-pyrazole-4-carbonitrile
(9i, C11H9N3)
Compound 9i was obtained from 4i when Vilsmeier–Haack
reagent was used at a 1:1 ratio. Yield 64 %; pale yellow
1
crystals; m.p.: 92–93 °C; MS (CI): m/z = 184 (MH?); H
NMR (300 MHz, DMSO-d6): d = 9.22 (s, 1H), 7.82 (d,
J = 8.1 Hz, 2H), 7.54 (t, J = 7.5 Hz, 2H), 7.40 (t,
J = 7.5 Hz, 1H), 2.40 (s, 3H) ppm; 13C NMR (75 MHz,
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Reaction of hydrazones derived from active methylene compounds
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