Chemistry of polyhalogenated nitrobutadienes, 14: Efficient synthesis of functionalized (Z)-2-allylidenethiazolidin-4-ones

Article abstract of DOI:10.3762/bjoc.10.170

The reaction of mercaptoacetic acid esters with pentachloro-2-nitro-1,3- butadiene (1) provides an appropriate precursor for the synthesis of special thiazolidin-4-ones. Applying different anilines as the second constituent for the requisite cyclization step, a series of (Z)-2-allylidenethiazolidin-4-ones was obtained in yields up to 81%. Some subsequent reactions have been examined too, such as the formation of perfunctionalized 1H-pyrazoles upon treatment with hydrazine. Thiazolidinones are as well known for their physiological activities as for their application in optoelectronics.

Full text of DOI:10.3762/bjoc.10.170

Chemistry of polyhalogenated nitrobutadienes, 14:
Efficient synthesis of functionalized
(Z)-2-allylidenethiazolidin-4-ones
Viktor A. Zapol’skii1, Jan C. Namyslo1, Mimoza Gjikaj2 and Dieter E. Kaufmann*1
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2014, 10, 1638–1644.
1Institute of Organic Chemistry, Clausthal University of Technology,
Leibnizstr. 6, 38678 Clausthal-Zellerfeld, Germany and 2Institute of
Inorganic and Analytical Chemistry, Clausthal University of
Technology, Paul-Ernst-Str. 4, 38678 Clausthal-Zellerfeld, Germany
doi:10.3762/bjoc.10.170
Received: 14 March 2014
Accepted: 26 June 2014
Published: 17 July 2014
Email:
Dieter E. Kaufmann* - dieter.kaufmann@tu-clausthal.de
Associate Editor: D. O'Hagan
* Corresponding author
© 2014 Zapol’skii et al; licensee Beilstein-Institut.
License and terms: see end of document.
Keywords:
atropisomers; cyclization; 2-nitroperchlorobutadiene; 1H-pyrazoles;
thiazolidin-4-ones
Abstract
The reaction of mercaptoacetic acid esters with pentachloro-2-nitro-1,3-butadiene (1) provides an appropriate precursor for the syn-
thesis of special thiazolidin-4-ones. Applying different anilines as the second constituent for the requisite cyclization step, a series
of (Z)-2-allylidenethiazolidin-4-ones was obtained in yields up to 81%. Some subsequent reactions have been examined too, such as
the formation of perfunctionalized 1H-pyrazoles upon treatment with hydrazine. Thiazolidinones are as well known for their physi-
ological activities as for their application in optoelectronics.
Introduction
Preliminary studies in the field of polyhalogenated nitrobutadi- accessible [2,5,16,17]. In this paper, we describe the formation
enes have already shown the enormous potential of pentachloro- of uniquely substituted thiazolidin-4-ones, a class of com-
2-nitro-1,3-butadiene (1) as a precursor for the “click synthesis” pounds which has proven to exhibit distinctive bioactivity, e.g.,
of highly functionalized (hetero)cyclic as well as acyclic com- antifungal, antibacterial, antitubercular, and anticonvulsant
pounds [1-15]. The corresponding syntheses that we have properties [18-28].
developed up to now [2-13], always start with the attack of an
appropriate nucleophile at the activated terminal carbon atom of Additionally, more recent studies often focus on their anti-
the nitrodichlorovinyl group within 1 to undergo a vinylic cancer [29-31] and anti-HIV potential [30,32]. Several 4-thiazo-
substitution. Thus, in case of, e.g., sulfur nucleophiles, the lidinone derivatives such as ralitoline (anticonvulsant), etozo-
corresponding thioperchlorobutadiene derivatives are easily line (antihypertensive), pioglitazone (hypoglycemic) and thia-
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zolidomycin (activity against streptomyces species) are already isomer in 80% yield (for further details see Supporting Informa-
in the market [33]. Beyond that, among industrial applications tion File 1). In contrast, the conversion of 1 (neat) with
thiazolidinones serve as electron donors, e.g., as ligands in 2.1 equivalents of methyl 2-mercaptoacetate (4) results in a
coordination compounds or as vulcanizing agents [31]. Further- mixture of methyl 2-((1,3,4,4-tetrachloro-2-nitrobuta-1,3-dien-
more, it is well known that these heterocycles play a major role 1-yl)thio)acetate (5) and 1,1-bis(methoxycarbonylmethylthio)-
in corresponding organic electronics, e.g., they lead to high 2-nitro-3,4,4-trichlorobuta-1,3-diene (6) after 10 days at room
quantum efficiency as donor compound in solar cells [34]. Very temperature with 67% and 29% yields, respectively. These
recently, thiazolidinones became a target in the field of nitrodienes 5 and 6 were separated by flash column chromatog-
photonics and optoelectronics, potentially applicable for revers- raphy and then characterized. Interestingly, the dithio com-
ible optical data storage, photo switching of optical elements, pound 6 was also accessible by treatment of the aforemen-
photochromic polymers, and similar applications [35].
tioned monothio derivative 5 with one equivalent of mercap-
toacetate 4. Following this pathway, the disubstituted diene 6
The background of thiazolidinone chemistry including classical was obtained in 80% yield (Scheme 1).
synthetic strategies has been reviewed comprehensively [18-
28,36-39]. Even though among possible synthetic pathways the The subsequent reaction of the mercaptoacetates 3 and 5 with
use of mercaptoacetic acid and its derivatives is well-estab- 2.1 equivalents of various arylamines is the key step of our thia-
lished [40-44], our approach, starting from a mercaptoacetic zolidin-4-one synthesis, that led to the corresponding (Z)-3-aryl-
acid derivative of perchloro-2-nitro-1,3-butadiene and an 2-(2,3,3-trichloro-1-nitroallylidene)thiazolidin-4-ones 7–18
aniline, is unprecedented up to now. In this context, it is very with up to 81% yield. As an example for the sequential reactiv-
interesting that the reaction of a 2-nitro-1-thioperchlorobuta- ity of the persubstituted allylidene side chain, the thiazolidin-4-
1,3-diene with N-nucleophiles usually yields a 1-amino-2-nitro- one 15 was reacted with p-tolylthiolate. Thereby, the C(2)–Cl
1-thioperchlorobuta-1,3-diene [16,45]. However, our novel ring position of the allylidene group was selectively substituted
closing reaction incorporates an arylamine as source for the by the reactive thiolate nucleophile, again in a SNVin-type
nitrogen of the thiazolidin-4-one heterocycle.
process, to give (Z)-3-(4-tolyl)-2-(3,3-dichloro-1-nitro-2-[4-
tolylthio]allylidene)thiazolidin-4-one (19) in 70% yield
(Scheme 2).
Results and Discussion
The reaction of pentachloro-2-nitro-1,3-butadiene (1) with
1.1 equivalents of ethyl 2-mercaptoacetate (2) at room tempera- According to proton NMR, the ring-closing step with the parent
ture without a solvent for 10 days furnished ethyl 2-((1,3,4,4- aniline or with one of its para-substituted derivatives in each
tetrachloro-2-nitrobuta-1,3-dien-1-yl)thio)acetate (3) as a single case led to a single N-arylthiazolidin-4-one isomer 7–15. In the
Scheme 1: SNVin reactions of pentachloro-2-nitro-1,3-butadiene (1).
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Scheme 2: Formation of thiazolidin-4-ones 7–19.
case of the ortho- or meta-substituted anilines 16–18 two atrop- bears the sulfur atom of the hetero ring as well as the nitro
isomers were generated. This phenomenon is due to a less group. The structural plot also gives an idea of the abovemen-
hindered rotation of the C–N bond of the former anilines tioned bulkiness, even in the case of the depicted para-substitu-
(Figure 1).
tion (Figure 2).
Figure 1: Hindered rotation in the case of ortho- or meta-substituted
aniline precursors.
The steric hindrance is additionally forcing by the s-cis con-
formation of the nitrobutadiene moiety (cf. Figure 2). A DFT
calculation of the energy barrier for rotation of the aromatic
substituent resulted in extraordinary high values of 169 and
191 kJ/mol for the ortho-methyl compound 18 and the larger,
but less rigid ortho-methoxy derivative 16, respectively. As
expected, the meta-anisyl derivative 17 showed a lower barrier
of 73 kJ/mol (see Supporting Information File 1). For compari-
son, the well-known atropisomer 1,1’-binaphthalene-2,2’-diol
Figure 2: X-ray analysis of thiazolidin-4-one 11.
(BINOL) shows a rotational barrier of 158 kJ/mol with calcu- The formation of the thiazolidin-4-ones 7–18 is assumed to
lated data in good accordance with the experimental value [46]. consist of three individual steps. In a SNVin type reaction with
the aniline derivative intermediate A (Scheme 3) is formed.
In addition to substantial NMR, IR, and mass spectral character- Subsequently, the thus introduced amino group attacks the car-
ization of the thiazolidinones 7–18, as an example the bonyl carbon of the mercaptoacetate moiety. This ring closure
4-iodophenyl substituted thiazolidinone 11 was subjected to affords the temporary imide hemiacetal B which is then stabi-
X-ray analysis (see Supporting Information File 1). This lized upon elimination of the corresponding alcohol to give the
confirmed the Z-configuration of the inner double bond which desired thiazolidin-4-ones 7–18 (Scheme 3).
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Beilstein J. Org. Chem. 2014, 10, 1638–1644.
Scheme 3: Assumed mechanism for the formation of thiazolidin-4-ones 7–18.
Furthermore, in addition to the anilines described above figuration according to the literature for similar compounds
(Scheme 2), we applied 1-naphthylamine as a bulkier aromatic [47,48]. Interestingly, close analogues of these structures, i.e.,
representative and morpholine as a secondary, more basic ali- the 5-arylmethylidene rhodanines, possess photosynthesis-
phatic amine. Conversion of 3 and 5 with morpholine and inhibiting and antialgal properties [49], show anticancer activity
1-naphthylamine afforded the open chain products 20 and 21 in [50,51], and are inhibitors of bacterial enzyme synthetase MurD
93% and 80% yield, respectively (Scheme 4), without a subse- with E. coli [52].
quent cyclization under one-pot conditions. Unexpectedly, even
under forcing conditions cyclization of isolated 21 did not take Additional treatment of thiazolidin-4-one 8 with a fivefold
place. Compound 21 was exclusively obtained as E-isomer. excess of hydrazine hydrate resulted in the formation of a
This was indicated by a proton NMR signal shifted downfield to 1H-pyrazole: A total of two hydrazine molecules were incorpo-
about 12 ppm due to a strong hydrogen bond between the amino rated into the final product, whereas two additional equivalents
hydrogen and the nitro group. In contrast, lacking the opportu- were consumed capturing hydrochloric acid. In this way, the
nity to build such a hydrogen bridge, the regiochemistry of 1H-pyrazole 27 with an exceptional substitution pattern was
compound 20 (also formed as one single isomer) remained obtained in 64% yield. The same reaction was applied to 5-aryl-
unclear.
methylidene-thiazolidin-4-one 25 which furnished the corres-
ponding 1H-pyrazole 28 in 52% yield (Scheme 5).
With the thiazolidinones in hand, in the case of 7, 8, 10, and 12
we carried out a Knoevenagel-type condensation with benzalde- A plausible multistep mechanism of this conversion is shown in
hyde and 3,4-dichlorobenzaldehyde in acetic acid at 118 °C in Scheme 6: Initially, a first molecule of the strong nucleophile
the presence of triethylamine. Thus, the 5-arylmethylidenethia- hydrazine is assumed to substitute the single C–Cl group within
zolidin-4-ones 22–26 were obtained in 68–94% yield. The pres- the trichlorovinyl subunit of 8 to give the intermediate I (SNVin
ence of only one signal for the benzylidene proton at reaction). Thereby, a second equivalent of hydrazine captures
7.83–7.98 ppm in the 1H NMR spectra of 22–26 suggested the hydrochloric acid. The amino group of the hydrazone then
formation of a single isomer, which was assigned to the Z-con- attacks the electrophilic C-2 position of the thiazolidinone. This
Scheme 4: Substitution reactions of the precursors 3 and 5 with additional amines.
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Beilstein J. Org. Chem. 2014, 10, 1638–1644.
Scheme 5: Synthesis of 5-arylmethylidenethiazolidin-4-ones 22–26 and 1H-pyrazoles 27, 28.
Scheme 6: Assumed mechanism for the formation of 1H-pyrazole 27.
way a threefold substituted 1H-pyrazole is formed (intermedi- from intermediate II, in the latter case 3-(3,4-dichlorophenyl)-
ate II) under ring opening of the thiazolidinone. In the course of 2-mercaptoacrylic acid is released.
the reaction, probably at this stage, the N-aryl amide is hydrazi-
nolysed to give the intermediate III, which is converted into the Moreover, nitrodiene 1 was subjected to a vinylic substitution
monohydrazino compound IV upon consumption of two further with ethyl 2-mercaptopropanoate to give ethyl 2-[(1,3,4,4-tetra-
equivalents of hydrazine. Finally, 27 is obtained upon elimina- chloro-2-nitrobuta-1,3-dien-1-yl)thio]propanoate (29) as an
tion of hydrochloric acid, caught by a fifth equivalent of inseparable mixture of Z- and E-isomers in a 4:1 ratio with 78%
hydrazine (Scheme 6). An analogous mechanism is also plau- total yield. Treatment of dienes (Z,E)-29 with different anilines
sible for the formation of pyrazole 28 from thiazolidinone 25. in ethanol at 0 °C to rt furnished (Z,E)-3-aryl-5-methylthiazo-
However, instead of the elimination of 2-mercaptoacetic acid lidinones 30–32. As an example, thiazolidinone 32 was reacted
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Beilstein J. Org. Chem. 2014, 10, 1638–1644.
Scheme 7: Formation of ethyl propanoate 29 and subsequent reactions.
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