New one-pot synthesis of 2-ylidenehydrazono-thiazoles

Article abstract of DOI:10.1080/17415993.2019.1635132

A new one pot reaction of substituted thiosemicarbazides with 2-bromoacetophenone and carbonyl compounds gave 2-hydrazonothiazoles in good yields. The structures of the isolated compounds were corroborated by NMR, IR, mass spectra and elemental analyses i

Full text of DOI:10.1080/17415993.2019.1635132

Journal of Sulfur Chemistry
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New one-pot synthesis of 2-ylidenehydrazono-
thiazoles
Ashraf A. Aly, Essmat M. El-Sheref, Alan B. Brown, Stefan Bräse, Martin
Nieger & El-Shimaa M. N. Abdelhafez
To cite this article: Ashraf A. Aly, Essmat M. El-Sheref, Alan B. Brown, Stefan Bräse, Martin
Nieger & El-Shimaa M. N. Abdelhafez (2019): New one-pot synthesis of 2-ylidenehydrazono-
thiazoles, Journal of Sulfur Chemistry, DOI: 10.1080/17415993.2019.1635132
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JOURNAL OF SULFUR CHEMISTRY
https://doi.org/10.1080/17415993.2019.1635132
New one-pot synthesis of 2-ylidenehydrazono-thiazoles
Ashraf A. Alya, Essmat M. El-Sherefa, Alan B. Brownb, Stefan Bräsec, Martin Niegerd and
El-Shimaa M. N. Abdelhafeze
aChemistry Department, Faculty of Science, Minia University El-Minia, Egypt; bChemistry Department, Florida
Institute of Technology, Melbourne, FL, USA; cInstitute of Organic Chemistry, Karlsruhe Institute of
Technology Karlsruhe, Germany; dDepartment of Chemistry, University of Helsinki Helsinki, Finland;
eMedicinal Chemistry Department, Faculty of Pharmacy, Minia University El-Minia, Egypt
ABSTRACT
ARTICLE HISTORY
Received 31 March 2019
Accepted 14 June 2019
A new one pot reaction of substituted thiosemicarbazides with 2-
bromoacetophenone and carbonyl compounds gave 2-hydrazono
thiazoles in good yields. The structures of the isolated compounds
were corroborated by NMR, IR, mass spectra and elemental analyses
in addition to X-ray structure determination.
KEYWORDS
Substituted
thiosemicarbazides;
2-bromoacetophenone;
carbonyl compounds;
2-ylidine-hydrazinothiazoles;
NMR; X-ray
Introduction
The 1,3-thiazole moiety is one of the most important scaffolds in heterocyclic chemistry
and drug design and discovery [1]. It is widely found in diverse pharmacologically active
substances and in some naturally-occurring compounds [1]. In recent years, many thia-
zole derivatives have been synthesized and subjected to various biological activity studies.
Thiazoles and their analogues serve as precursors for the synthesis of biologically active
compounds [2]. They were reported to possess antimicrobial [3–6], analgesic [7], anti-
inflammatory [8], anticonvulsant [9], cardiotonic [10], anticancer [11–13], antitubercular
[14] and anthelmintic [15] effects.
It was reported that substituted 2-hydrazino-1,3-thiazoles show an inhibitory activ-
ity (MIC of 16 l μg/mL) against a resistant strain of Candida krusei [16]. Only a few
other 2-hydrazino-1,3-thiazole analogues that exhibit significant antimicrobial activity
have recently been reported in the literature [17]. Thiazoles bearing a bicyclic or hetero-
cyclic ring on a hydrazone functionality and a phenyl at the C-4 position of the thiazole
CONTACT Ashraf A. Aly
ashrafaly63@yahoo.com
Chemistry Department, Faculty of Science, Minia University,
61519 El-Minia, Egypt
© 2019 Informa UK Limited, trading as Taylor & Francis Group

2
A. A. ALY ET AL.
nucleus are particularly active and present micromolar or submicromolar MIC activity
against several Candida spp. Strains (repeated) [1]. Thus, such scaffolds are an interesting
starting point for further optimization of novel antifungal agents.
Several methods for the synthesis of thiazole derivatives have been developed [18–20],
the most widely used is the Hantzsch synthesis, which uses thioamides and α-halocarbonyl
(or α-halo ester) compounds as starting materials [21]. It was previously shown that yli-
denes of hydrazinothiazoles could be synthesized by two different methods: a) reaction
of hydrazinothiazoles with the appropriate ketones or aldehydes or b) reaction between
thiosemicarbazides and 2-bromoacetophenones. The yields of the methods described suf-
fer from long reaction times. In this manuscript, we have designed a new facile method
in order to prepare ylidenes of hydrazonothiazoles in a one pot reaction starting from
substituted thiosemicarbazides, 2-bromoacetophenones and ketones.
Results and Discussion
The compounds 3a-c [22,23] were previously prepared by reaction of substituted thiosemi-
carbazides 1a-c with 2-bromoacetophenone (2) (Scheme 1, method A). On the other hand,
reaction of 1a-c with appropriate ketones 4a,b, gave the corresponding thiosemihydra-
zones 5a-e [24–28] and upon subjecting compounds 5a-e to bromide 2, the corresponding
2-ylidenes of hydrazinothiazoles 6a-e were obtained in moderate yields (Scheme 1, method
B). The yields of the products 6a-e (i.e. preparation of compounds 6a-d according to the
literature [29–31]) using the two aforesaid procedures were not optimal (Scheme 1).
We herein reported a new one-pot method using a mixture of 1a-c, 2 and 4a,b (Scheme
1, method C). The yields of this one-pot method are far superior to those obtained by
methods A and C. The X-ray structure confirmed the identity of 6a as shown in Figure 1. It
further established the stereochemistry of the CNN moiety as Z, s-trans (transoid) conclu-
sively establishing its structure as (Z,s-trans)-3,4-diphenyl-propan-2-ylidenehydrazono-
2,3-dihydrothiazole.
The yields of compounds 6a-e using the Method C are shown in Table 1. In comparison,
as examples, the yields of compound 6a,c with those reported by Method B, we can find
Scheme 1. Synthesis of 2-ylidenes of hydrazonothiazoles 6a-e.

JOURNAL OF SULFUR CHEMISTRY
3
Figure 1. Molecular structure of 6a (displacement parameters are drawn at 50% probability level).
Table 1. Yields of compounds 6a-e using methods C and those reported by
B.
Compound
Yield (%) from Method C
Yield (%) from Method B
88 [24]
6a
6b
6c
6d
6e
92
95
93
78
94
70 [25]
out the advantages of our procedure. In addition time and chemicals were conserved by
our new method.
Conclusion
In this paper, we have illustrated a new method of synthesizing hydrazonothiazoles by
a one-pot reaction consisting of substituted thiosemicarbazides, 2-bromoacetophenones
and ketones. The advantages of our new method are; a) high yields of the products, b)
facile one pot method and c) the absence of any additives.
Experimental
General
Melting points were determined using an APP Digital ST 15 melting point apparatus
and uncorrected. TLC analyses were performed using analytical Merck 9385 silica alu-
minum sheets (Kieselgel 60) with PF254 indicator. The IR spectra were recorded as KBr
disks on Shimadzu-408 infrared spectrophotometer, Faculty of Science, Minia University.

4
A. A. ALY ET AL.
The NMR spectra were measured using a Bruker AV-400 spectrometer at Florida Insti-
tute of Technology, Melbourne, FL, USA. Chemical shifts were expressed as δ (ppm) with
tetramethylsilane as internal reference. The samples were dissolved in CDCl3 and DMSO-
d6, s = singlet, d = doublet, dd = doublet of doublet and t = triplet. Mass spectrometry
were recorded on a Varian MAT 312 instrument in EI mode (70 eV), at the Karlsruhe Insti-
tut für Technologie (KIT), Institute of Organic Chemistry, Karlsruhe, Germany. Elemental
analyses were carried out using Varian Elementary device in National Research Center,
Giza, Egypt.
Crystal structure determination of 6a
The single-crystal X-ray diffraction study was carried out on a Bruker D8 Venture diffrac-
tometer with Photon100 detector at 123(2) K using Cu-Kα radiation (λ = 1.54178 Å).
Dual space methods (SHELXT) [32] were used for structure solution and refinement
was carried out using SHELXL-2014 (full-matrix least-squares on F2) [33]. Hydrogen
atoms were refined using a riding model. A semi-empirical absorption correction and an
extinction correction were applied.
6a: Yellow crystals, C18H17N3S, Mr = 307.40, crystal size 0.20 × 0.08 × 0.04 mm, mon-
oclinic, space group P21/c (No. 14), a = 5.8645(2) Å, b = 14.0488(5) Å, c = 18.7533(7)
Å, β = 97.003(2)°, V = 1533.11(10) Å3, Z = 4, ρ = 1.332 Mg/m−3, µ(Cu-Kα) = 1.857
mm−1, F(000) = 648, 2θ
= 144.4°, 16566 reflections, of which 3015 were independent
max
(Rint = 0.025), 202 parameters, R1 = 0.029 (for 2856 I > 2σ(I)), wR2 = 0.072 (all data),
S = 1.04, largest diff. peak / hole = 0.255 / −0.240 e Å−3
.
CCDC 1896104 (6a) contains the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Starting materials
Compounds 3a-c and 5a-e were prepared according to literature [22] and [23], respectively
(see their corresponding references). Compounds 6a-d were prepared for comparison
according to the literature [24]. The NMR assignments were made with a combination
of COSY, HSQC, and HMBC experiments.
General procedure describes preparation of compounds 6a-e
A mixture of 1a-c, 2 and 4a,b (1 mmol) in absolute ethanol (EtOH, 150 mL), was refluxed
with stirred at room temperature for 6–10 h (the reaction was monitored by TLC). The
reaction mixture was allowed to stand overnight. The formed products were recrystallized
from the stated solvents.
(Z)-3,4-Diphenyl-2-(propan-2-ylidenehydrazono)-2,3-dihydrothiazole (6a). Pale yellow
crystals (EtOH), yield: 0.283 g (92%), Rf = 0.6 (Toluene: AcOEt; 10:1), m.p. 165–167°C
(m.p. [24] 165°C). 1H NMR (400 MHz, DMSO-d6): δ = 7.33 (t, 2H, J = 7.5 Hz, Ar-H-m),
7.25–7.22 (m, 6H, Ar-H-o, m’, p, p’), 7.17–7.15 (m, 2H, Ar-H-o’), 6.51 (s, 1H, H-5), 1.91 (s,
3H, CH3), 1.79 (s, 3H, CH3); 13C NMR (400 MHz, DMSO-d6): δ = 165.9 (C-2), 158.9,

JOURNAL OF SULFUR CHEMISTRY
5
139.1, 138.1, 131.1 (Ar-C), 128.5 (Ar-2CH-m), 128.3, 128.2 (Ar-2CH-o,m’), 128.1 (Ar-
CH-p,p’), 127.9 (Ar-2CH-o’), 127.2 (Ar-CH-p, p’), 101.0 (thiazole-C-5), 24.3, 18.7 (CH3).
15N (NMR, DMSO-d6): δ = 344.5 (azomethine-N), 138.5 (thiazole-N). Anal. Calcd. For
C18H17N3S (307.42): C, 70.33; H, 5.57; N, 13.67. Found: C, 70.22; H, 5.45; N, 13.55.
(Z)-3,4-Diphenyl-2-((E)-1-phenylethylidene)hydrazono)-2,3-dihydrothiazole (6b). Pale
yellow crystals (EtOH), yield: 0.350 g (95%), Rf = 0.4 (Toluene: AcOEt; 10:1), m.p.
1
310–312°C (m.p. [25] 310–312°C). H NMR (400 MHz, DMSO-d6): δ = 7.81 (dd, 2H,
J = 8.0, 1.50 Hz, Ar-H-o), 7.38–7.36 (m, 5H, Ar-H-m, m’’,p’’), 7.32–7.29 (m, 3H, Ar-H-
o,p/p’), 7.27–7.25 (m, 3H, Ar-H- H-m’, p’/p), 7.21–7.20 (m, 2H, Ar-H- H-o’), 6.66 (s, 1H,
H-5), 2.20 (s, 3H, CH3), 13C NMR (400 MHz, DMSO-d6): δ = 168.9 (C-2), 155.8, 139.6,
138.3, 137.7, 130.8 (Ar-C), 128.9 (Ar-CH-p’’), 128.7, 128.4 (Ar-2CH-o’), 128.3 (Ar-CH-
p,p’), 128.2 (Ar-2CH-m’), 128.1 (Ar-2CH-m’’), 128.0 (Ar-2CH-o’), 127.6 (Ar-CH-p,p’),
125.9 (Ar-2CH-o’), 102.0 (thiazole-C-5), 14.4 (CH3). 15N (NMR, DMSO-d6): δ = 354.1
(azomethine-N), 142.6 (thiazole-N). Anal. calcd. for C23H19N3S (369.49): C, 74.77; H,
5.18; N, 11.37. Found: C, 74.62; H, 5.00; N, 11.25.
(Z)-3-Allyl-4-phenyl-2-(E)-1-phenylethylidene)hydrazono)-2,3-dihydrothiazole (6c).
Pale yellow crystals (CH3CN), yield: 0.310 g (93%), Rf = 0.45 (Toluene: AcOEt; 10:1),
m.p. 247–249°C (m.p. [25] 246–248°C). 1 H NMR (400 MHz, DMSO-d6): δ = 7.54–7.44
(m, 4H, Ar-CH), 7.34–7.21 (m, 6H, Ar-CH), 7.12 (s, 1H, H-5), 5.65–5.63 (m, 1H, allyl-
CH), 5.28–5.24 (m, 2H, allyl-CH2-), 4.49 (br, 2H, allyl-CH2N), 2.31 (s, 3H, CH3); 13C
NMR (100 MHz, DMSO-d6): δ = 163.0 (thiazole-C), 158.9, 142.2, 137.9, 141.5 (Ar-C),
135.7 (Allyl-CH), 130.2, 129.2, 128.9, 128.2, 127.8, 126.7 (Ar-CH), 116.7 (Ally-CH2), 106.2
(thiazole-CH-5), 45.8 (Allyl-CH2N), 14.44 (CH3); Anal. calcd. for C20H19N3S (333.45): C,
72.04; H, 5.74; N, 12.60. Found: C, 72.16; H, 5.80; N, 12.46.
(Z)-3-Ethyl-4-phenyl-2-propan-2-ylidene)hydrazono)-2,3-dihydrothiazole (6d). Pale
yellow crystals (CH3OH), yield: 0.202 g (78%), m.p. =97–98°C (lit [25] 96°C). 1H NMR
(400 MHz, CDCl3): δ = 7.78–7.76 (m, 2H, Ph-H), 7.50-.46 (m, 3H, Ph-H), 7.10 (s, 1H,
thiazole-5), 4.00 (q, 2H, J = 7.0 Hz, CH2-ethyl), 2.40 (s, 3H, CH3), 1.98 (s, 3H, CH3), 1.20
(t, 3H, J = 7.0 Hz, CH3-ethyl). 13C NMR (400 MHz, CDCl3): δ = 168.0, 158.0 (C = N),
139.4 (C-4-thiazole), 136.5 (Ph-C), 128.6, 127.0 (Ph-2CH), 126.0 (Ph-CH), 103.0 (thiazole-
CH-5), 39.4 (CH2-ethyl), 22.4, 21.0 (CH3), 13.0 (CH3-ethyl). Anal. calcd. for C14H17N3S
(259.37): C, 64.83; H, 6.61; N, 16.20. Found: C, 64.70; H, 6.81; N, 16.36.
(Z)-3-Ethyl-4-phenyl-2-(E)-1-phenylethylidene)hydrazono)-2,3-dihydrothiazole (6e).
Pale yellow crystals (CH3OH), yield: 0.302 g (94%), Rf = 0.3 (Toluene: AcOEt; 10:1),
m.p. = 212–214 °C. 1H NMR (400 MHz, CDCl3): δ = 7.80–7.78 (m, 2H, Ph-H), 7.60–7.40
(m, 4H, Ph-H), 6.92 (s, 1H, thiazole-5), 6.86–6.82 (m, 4H, Ph-H), 4.00 (q, 2H, J = 7.0 Hz,
CH2-ethyl), 2.40 (s, 3H, CH3), 1.20 (t, 3H, J = 7.0 Hz, CH3-ethyl). 13C NMR (400 MHz,
CDCl3): δ = 164.0, 155.0 (C = N), 139.0 (C-4-thiazole), 137.0 (Ph-2C), 132.0, 131.0,
130.6, 130.0 (Ph-2CH), 127.0, 126.2 (Ph-CH), 102.0 (Thiazole-CH-5), 38.9 (CH2-ethyl),
21.0, 13.0 (CH3). Anal. calcd. for C19H19N3S (321.44): C, 71,00; H, 5.96; N, 13.07. Found:
C, 71.10; H, 6.00; N, 13.12.
Acknowledgements
The NMR spectrometer at Florida Institute of Technology was purchased with assistance from the
U.S. National Science Foundation (CHE 03-42251).

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A. A. ALY ET AL.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
The NMR spectrometer at Florida Institute of Technology was purchased with assistance from the
U.S. National Science Foundation (CHE 03-42251).
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