Synthesis and Properties of Alkyl 2-[2-(Diarylmethylidene)hydrazinyl]-5,5-dimethyl-4-oxohex-2-enoates

Article abstract of DOI:10.1134/S1070428020040132

Abstract: Ring opening of 3-[(diarylmethylidene)hydrazinylidene]-5-tert-butylfuran-2(3H)-ones by the action of alcohols afforded previously unknownalkyl 2-[2-(diarylmethylidene)hydrazinyl]-5,5-dimethyl-4-oxohex-2-enoates whichwere found to exist in soluti

Full text of DOI:10.1134/S1070428020040132

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2020, Vol. 56, No. 4, pp. 649–653. © Pleiades Publishing, Ltd., 2020.
Russian Text © The Author(s), 2020, published in Zhurnal Organicheskoi Khimii, 2020, Vol. 56, No. 4, pp. 613–618.
Synthesis and Properties
of Alkyl 2-[2-(Diarylmethylidene)hydrazinyl]-
5,5-dimethyl-4-oxohex-2-enoates
A. I. Siutkinaa,*, N. M. Igidova, and I. A. Kizimovaa
a Perm State Pharmaceutical Academy, Ministry of Health of the Russian Federation, Perm, 614990 Russia
*e-mail: syutkina.alyona@yandex.ru
Received September 2, 2019; revised February 19, 2020; accepted February 19, 2020
Abstract—Ring opening of 3-[(diarylmethylidene)hydrazinylidene]-5-tert-butylfuran-2(3H)-ones by the action
of alcohols afforded previously unknown alkyl 2-[2-(diarylmethylidene)hydrazinyl]-5,5-dimethyl-4-oxohex-2-
enoates which were found to exist in solution as mixtures of tautomers.
Keywords: 2,4-dioxobutanoic acid esters, ring opening of 3-hydrazinylidenefuran-2(3H)-ones, primary and
secondary alcohols, tautomers
DOI: 10.1134/S1070428020040132
3-Hydrazinylidene(imino)furan-2(3H)-ones consti-
tute a promising class of furan derivatives due to their
synthetic accessibility [1–5] and high reactivity [6–16].
We recently reported the reaction of 5-tert-butyl-3-
[(9H-fluoren-9-ylidene)hydrazinylidene]furan-2(3H)-
one with NH nucleophiles, which afforded [2-(9H-fluo-
ren-9-ylidene)hydrazinyl]-5,5-dimethyl-4-oxo-2-hex-
2-enamides [17]. Furthermore, previous studies have
shown that 3-imino(hydrazinylidene)furan-2(3H)-ones
undergo ring opening in reactions with OH nucleo-
philes to give alkyl aroylpyruvates [10, 18]. There are
no published data on chemical transformations of
structurally related 3-[(arylmethylidene)hydrazinyli-
dene]-5-tert-butyl-3H-furan-2-ones in reactions with
alcohols. Then, the present work was aimed at studying
this reaction and the properties of the products.
dene)hydrazinylidene]furan-2(3H)-one (1d). Instead,
the corresponding ketone azines 3a and 3b were
isolated (Scheme 2). Similar rearrangement of the
target product into azine was described in [19]. We also
found that compounds 1a–1d did not react with
sterically hindered 2-methylpropan-2-ol, and only un-
changed initial compounds were isolated.
The IR spectra of 2a–2i in mineral oil showed
absorption bands in the region 1735–1740 cm–1 due to
stretching vibrations of the ester carbonyl group and at
1553–1621 cm–1 due to ketone carbonyl involved in
intramolecular hydrogen bond N–H···O=C, as well as
C=C and C=N bonds.
1
According to the H NMR data, compounds 2a–2d
in DMSO-d6 solution exist as equilibrium mixtures of
enehydrazine (A, B) and hydrazone tautomers (C, D).
Enehydrazino ketone structures A and B characteris-
tically displayed a singlet from the C3H=C proton at
δ 5.47–5.52 and 5.52–5.58 ppm and a broadened
singlet of the NH proton at δ 12.01–12.02 and 12.10–
12.12 ppm, respectively. The downfield position of the
NH singlet is rationalized by intramolecular hydrogen
bonding with the C4=O carbonyl group. The overall
concentration of tautomers A and B ranges from 55 to
60%, and the equilibrium is shifted toward structure A
(30–35%), which does not contradict published data
[5, 19]. Ketohydrazones C (E) and D (Z) are charac-
terized by a two-proton singlet for methylene protons
on C3 at δ 4.02–4.04 and 4.01–4.02 ppm, respectively.
Reactions of 3-[(arylmethylidene)hydrazinylidene]-
5-tert-butyl-3H-furan-2-ones 1a and 1b with alcohols
in the absence of a catalyst gave alkyl 2-[2-(diaryl-
methylidene)hydrazinyl]-5,5-dimethyl-4-oxohex-2-
enoates 2a–2i in low yields. The yield was considerably
improved when a catalytic amount of triethylamine
was added to the reaction mixture (Scheme 1). Com-
pounds 2a–2i are pale yellow crystalline solids soluble
in toluene, diethyl ether, and acetonitrile and insoluble
in propan-2-ol, ethanol, and water.
We failed to obtain esters 2 from 5-tert-butyl-3-
[(1,2-diphenyl-2-oxoethylidene)hydrazinylidene]furan-
2(3H)-one (1c) or 5-tert-butyl-3-[(9H-fluoren-9-yli-
649

SIUTKINA et al.
650
Scheme 1.
R1
R2
R2
N
R1
R1
N
R2
R3OH, Et3N
H
N
O
H
N
O
N
O
N
O
OR3
OR3
t-Bu
t-Bu
t-Bu
O
O
1a, 1b
A
B
R1
N
R2
R2
N
R1
N
O
N
O
O
O
OR3
OR3
t-Bu
t-Bu
C
2a–2i
D
1, R1 = Ph, R2 = 4-MeOC6H4 (a); R1 = R2 = Ph (b); 2, R1 = Ph, R2 = 4-MeOC6H4, R3 = Me (a), Et (b), Bu (c),
MeCH2C(Me)2CH2 (d); R1 = R2 = Ph, R3 = Me (e), Et (f), i-Pr (g), Bu (h), MeCH2C(Me)2CH2 (i).
Structure C predominates over D, presumably due to
EXPERIMENTAL
steric and energy factors.
The progress of reactions was monitored, and the
purity of the isolated compounds was checked, by TLC
on Silufol plates using diethyl ether–benzene–acetone
(10:9:1) as eluent; spots were visualized by treatment
with iodine vapor. The IR spectra were recorded on
an FSM-1202 spectrometer with Fourier transform
The 1H NMR spectra of 2e–2i in DMSO-d6 differed
from the spectra of 2a–2d, since they contained signals
from only two tautomers, enehydrazine A and hydra-
zone C. In particular, tautomer A gave rise to olefinic
proton signal at δ 5.54–5.60 ppm and NH signal at
δ 12.04–12.10 ppm, and structure C was characterized
by a two-proton singlet at δ 4.01–4.05 ppm for C3H2
methylene group. The fraction of tautomer A was es-
1
from samples dispersed in mineral oil. The H NMR
spectra were recorded on a Bruker Avance III HD
spectrometer at 400 MHz using DMSO-d6 as solvent.
The mass spectra (electron impact, 70 eV) were
obtained with a Finnigan MAT INCOS 50 instrument.
Elemental analysis was performed on a Leco CHNS-
932 analyzer. The melting (decomposition) points were
measured with a PTP-2 melting point apparatus.
Compounds 1a–1d were synthesized according to the
procedures described in [17, 20–21].
1
timated at 65–98% on the basis of the H NMR signal
intensities, presumably due to additional stabilization
of that structure by intramolecular hydrogen bond
C4=O···H–N.
The assigned structures were also confirmed by the
mass spectra of 2a and 2e, which showed the corre-
sponding molecular and fragment ion peaks.
Scheme 2.
R1
N
R2
H
N
R1
N
O
OR3
R2
t-Bu
N
R3OH, Et3N
O
R1
t-Bu
O
O
R1
N
1c, 1d
N
R2
R2
3a, 3b
1c, 3a, R1 = Ph, R2 = COPh; 1d, 3b, R1R2 = 1,1′-biphenyl-2,2′-diyl.
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SYNTHESIS AND PROPERTIES OF ALKYL 2-[2-(DIARYLMETHYLIDENE)...
651
General procedure for the synthesis of com-
pounds 2a–2i. A mixture of 0.001 mol of compound
1a or 1b, 20 mL of ethanol, and 0.2 mmol (20 mol %)
of triethylamine was refluxed for 5 min until a yellow
solution was formed. The mixture was cooled, and the
precipitate was filtered off and purified by recrystal-
lization from an appropriate solvent.
spectrum, δ, ppm: A (30%): 0.81–0.91 m (3H,
CH2CH3), 0.99 s (9H, t-Bu), 1.20–1.74 m (4H,
CH2CH2), 3.76 s (3H, OCH3), 4.33 t (2H, OCH2),
5.47 s (1H, CH), 6.91–7.68 m (9H, Harom), 12.01 br.s
(1H, NH); B (25%): 0.81–0.91 m (3H, CH2CH3),
1.08 s (9H, t-Bu), 1.20–1.74 m (4H, CH2CH2), 3.80 s
(3H, OCH3), 4.09 t (2H, OCH2), 5.53 s (1H, CH),
6.91–7.68 m (9H, Harom), 12.10 br.s (1H, NH);
C (24%): 0.81–0.91 m (3H, CH2CH3), 1.01 s (9H,
t-Bu), 1.20–1.74 m (4H, CH2CH2), 3.88 s (3H, OCH3),
4.02 s (2H, CH2), 4.14 t (2H, OCH2), 6.91–7.68 m (9H,
Harom); D (21%): 0.81–0.91 m (3H, CH2CH3), 1.05 s
(9H, t-Bu), 1.20–1.74 m (4H, CH2CH2), 3.81 s (3H,
OCH3), 4.01 s (2H, CH2), 4.33 t (2H, OCH2), 6.91–
7.68 m (9H, Harom). Found, %: C 71.52; H 7.35;
N 6.45. C26H32N2O4. Calculated, %: C 71.53; H 7.39;
N 6.42. M 436.55.
Methyl 2-{2-[(4-methoxyphenyl)(phenyl)methyli-
dene]hydrazinyl}-5,5-dimethyl-4-oxohex-2-enoate
(2a). Yield 0.33 g (85%), pale yellow crystals, mp 145–
147°C (from EtOH). IR spectrum, ν, cm–1: 1740
(C=O), 1613, 1553 (C=C, C=N). 1H NMR spectrum, δ,
ppm: A (35%): 0.98 s (9H, t-Bu), 3.76 s (3H, OCH3),
3.90 s (3H, OCH3), 5.52 s (1H, CH), 6.93–7.66 m (9H,
Harom), 12.02 br.s (1H, NH); B (25%): 1.01 s (9H,
t-Bu), 3.79 s (3H, OCH3), 3.87 s (3H, OCH3), 5.58 s
(1H, CH), 6.93–7.66 m (9H, Harom), 12.12 br.s (1H,
NH); C (22%): 1.07 s (9H, t-Bu), 3.67 s (3H, OCH3),
3.83 s (3H, OCH3), 4.04 s (2H, CH2), 6.93–7.66 m
(9H, Harom); D (18%): 1.04 s (9H, t-Bu), 3.71 s (3H,
OCH3), 3.90 s (3H, OCH3), 4.02 s (2H, CH2), 6.93–
7.66 m (9H, Harom). Mass spectrum, m/z (Irel, %): 394
(24) [M]+, 337 (100) [M – t-Bu]+, 335 (11) [M –
COOCH3]+, 309 (33) [M – t-BuCO]+, 210 (78)
[Ph2C=N]+, 77 (25) [Ph]+, 57 (31) [t-Bu]+. Found, %:
C 70.05; H 6.63; N 7.09. C23H26N2O4. Calculated, %:
C 70.03; H 6.64; N 7.10. M 394.47.
2,2-Dimethylbutyl 2-{2-[(4-methoxyphenyl)-
(phenyl)methylidene]hydrazinyl}-5,5-dimethyl-4-
oxohex-2-enoate (2d). Yield 0.39 g (83%), pale yellow
crystals, mp 88–90°C (from EtOH). IR spectrum, ν,
cm–1: 1739 (C=O), 1617, 1561 (C=C, C=N, C=Ochel).
1H NMR spectrum, δ, ppm: A (31%): 0.78–0.86 m
(3H, CH3), 0.99 s (9H, t-Bu), 1.14–1.40 m (6H, CH3),
1.48–1.77 m (2H, CH2CH3), 3.76 s (3H, OCH3), 4.32 t
(2H, OCH2), 5.47 s (1H, CH), 6.91–7.68 m (9H, Harom),
12.01 br.s (1H, NH); B (25%): 0.78–0.86 m (3H, CH3),
1.07 s (9H, t-Bu), 1.14–1.40 m (6H, CH3), 1.48–1.77 m
(2H, CH2CH3), 3.88 s (3H, OCH3), 4.09 t (2H, OCH2),
5.52 s (1H, CH), 6.91–7.68 m (9H, Harom), 12.10 br.s
(1H, NH); C (23%): 0.78–0.86 m (3H, CH3), 1.01 s
(9H, t-Bu), 1.14–1.40 m (6H, CH3), 1.48–1.77 m (2H,
CH2CH3), 3.80 s (3H, OCH3), 4.02 s (2H, CH2), 4.32 t
(2H, OCH2), 6.91–7.68 m (9H, Harom); D (21%): 0.78–
0.86 m (3H, CH3), 1.05 s (9H, t-Bu), 1.14–1.40 m (6H,
CH3), 1.48–1.77 m (2H, CH2CH3), 3.81 s (3H, OCH3),
4.01 s (2H, CH2), 4.13 t (2H, OCH2), 6.91–7.68 m
(9H, Harom). Found, %: C 71.52; H 7.35; N 6.45.
C28H38N2O4. Calculated, %: C 72.39; H 7.81; N 6.03.
M 436.55.
Ethyl 2-{2-[(4-methoxyphenyl)(phenyl)methyli-
dene]hydrazinyl}-5,5-dimethyl-4-oxohex-2-enoate
(2b). Yield 0.38 g (94%), pale yellow crystals,
mp 127–129°C (from EtOH). IR spectrum, ν, cm–1:
1737 (C=O), 1621, 1558 (C=C, C=H, C=Ochel).
1H NMR spectrum, δ, ppm: A (32%): 0.99 s (9H, t-Bu),
1.36 t (3H, CH2CH3), 3.76 s (3H, OCH3), 4.38 q (2H,
CH2CH3), 5.48 s (1H, CH), 6.92–7.65 m (9H, Harom),
12.02 br.s (1H, NH); B (25%): 1.01 s (9H, t-Bu), 1.15 t
(3H, CH2CH3), 3.80 s (3H, OCH3), 4.14 q (2H,
CH2CH3), 5.53 s (1H, CH), 6.92–7.65 m (9H, Harom),
12.12 br.s (1H, NH); C (23%): 1.08 s (9H, t-Bu), 1.33 t
(3H, CH2CH3), 3.88 s (3H, OCH3), 4.03 s (2H, CH2),
4.38 q (2H, CH2CH3), 6.92–7.65 m (9H, Harom);
D (20%): 1.05 s (9H, t-Bu), 1.19 t (3H, CH2CH3),
3.82 s (3H, OCH3), 4.01 s (2H, CH2), 4.18 q (2H,
CH2CH3), 6.92–7.65 m (9H, Harom). Found, %:
C 70.59; H 6.90; N 6.84. C24H28N2O4. Calculated, %:
C 70.57; H 6.91; N 6.86. M 408.50.
Methyl 2-[2-(diphenylmethylidene)hydrazinyl]-
5,5-dimethyl-4-oxohex-2-enoate (2e). Yield 0.35 g
(96%), pale yellow crystals, mp 152–154°C (from
EtOH). IR spectrum, ν, cm–1: 1739 (C=O), 1619, 1560
1
(C=C, C=N, C=Ochel). H NMR spectrum, δ, ppm:
A (88%): 1.01 s (9H, t-Bu), 3.93 s (3H, OCH3), 5.60 s
(1H, CH), 7.29–7.68 m (10H, Harom), 12.05 s (1H,
NH); C (12%): 1.08 s (9H, t-Bu), 3.70 s (3H, OCH3),
4.05 s (2H, CH2), 7.29–7.68 m (10H, Harom). Mass
spectrum, m/z (Irel, %): 364 (12) [M]+, 307 (100)
[M – t-Bu]+, 305 (6) [M – COOCH3]+, 279 (16)
Butyl 2-{2-[(4-methoxyphenyl)(phenyl)methyli-
dene]hydrazinyl}-5,5-dimethyl-4-oxohex-2-enoate
(2c). Yield 0.38 g (87%), pale yellow crystals, mp 107–
109°C (from EtOH). IR spectrum, ν, cm–1: 1738
1
(C=O), 1618, 1561 (C=C, C=N, C=Ochel). H NMR
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SIUTKINA et al.
652
[M – t-BuCO]+, 181 (9) [Ph2C=N]+, 77 (33) [Ph]+, 57
(23) [t-Bu]+. Found, %: C 72.52; H 6.60; N 7.68;
O 13.15. C22H24N2O3. Calculated, %: C 72.51; H 6.64;
N 7.69; O 13.17. M 364.44.
1.01 s (9H, t-Bu), 1.26–1.40 m (6H, CH3), 1.70–1.77 m
(2H, CH2CH3), 4.35 t (2H, OCH2), 5.56 s (1H, CH),
7.28–7.70 m (10H, Harom), 12.06 s (1H, NH); C (10%):
0.80–0.87 m (3H, CH3), 1.08 s (9H, t-Bu), 1.26–1.40 m
(6H, CH3), 1.51–1.58 m (2H, CH2CH3), 4.04 s (2H,
CH2), 4.12 t (2H, OCH2), 7.28–7.70 m (10H, Harom).
Found, %: C 74.65; H 7.88; N 6.42; O 11.03.
C27H34N2O3. Calculated, %: C 74.62; H 7.89; N 6.45;
O 11.04. M 434.58.
Ethyl 2-[2-(diphenylmethylidene)hydrazinyl]-
5,5-dimethyl-4-oxohex-2-enoate (2f). Yield 0.37 g
(98%), pale yellow crystals, mp 142–144°C (from
EtOH). IR spectrum, ν, cm–1: 1739 (C=O), 1615, 1554
1
(C=C, C=N, C=Ochel). H NMR spectrum, δ, ppm:
A (65%): 1.00 s (9H, t-Bu), 1.35 t (3H, CH2CH3),
4.39 q (2H, CH2CH3), 5.54 s (1H, CH), 7.27–7.69 m
(10H, Harom), 12.04 br.s (1H, NH); C (35%): 1.07 s
(9H, t-Bu), 1.16 t (3H, CH2CH3), 4.01 s (2H, CH2),
4.15 q (2H, CH2CH3), 7.27–7.69 m (10H, Harom).
Found, %: C 72.95; H 6.90; N 7.43; O 12.69.
C23H26N2O3. Calculated, %: C 72.99; H 6.92; N 7.40;
O 12.68. M 378.47.
CONFLICT OF INTEREST
The authors declare the absence of conflict of interest.
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CH(CH3)2], 5.17–5.27 m [1H, CH(CH3)2], 5.55 s (1H,
CH), 7.28–7.69 m (10H, Harom), 12.10 s (1H, NH);
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1
(C=C, C=N, C=Ochel). H NMR spectrum, δ, ppm:
A (98%): 0.90 t (3H, CH3), 1.01 s (9H, t-Bu), 1.36–
1 . 4 5 m ( 2 H , C H 2 C H 3 ) , 1 . 6 9 – 1 . 7 5 m ( 2 H ,
CH2CH2CH3), 4.36 t (2H, OCH2), 5.56 s (1H, CH),
7.28–7.70 m (10H, Harom), 12.06 s (1H, NH); C (2%):
0.84 t (3H, CH3), 1.08 s (9H, t-Bu), 1.21–1.29 m (2H,
CH2CH3), 1.49–1.57 m (2H, CH2CH2CH3), 4.04 s (2H,
CH2), 4.12 t (2H, OCH2), 7.28–7.70 m (10H, Harom).
Found, %: C 73.82; H 7.46; N 6.91; O 11.82.
C25H30N2O3. Calculated, %: C 73.86; H 7.44; N 6.89;
O 11.81. M 406.53.
2,2-Dimethylbutyl 2-[2-(diphenylmethylidene)-
hydrazinyl]-5,5-dimethyl-4-oxohex-2-enoate (2i).
Yield 0.33 g (77%), pale yellow crystals, mp 119–
120°C (from EtOH). IR spectrum, ν, cm–1: 1738
1
(C=O), 1619, 1559 (C=C, C=N, C=Ochel). H NMR
spectrum, δ, ppm: A (90%): 0.80–0.87 m (3H, CH3),
https://doi.org/10.1134/S1070428013090170
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