A convenient one-pot synthesis of novel functionalized thiophene, thieno[2,3-b] thiophene, thiopyran, and thiopyrano[2,3-b]thiopyran bearing phosphonate groups

Article abstract of DOI:10.1080/17415993.2021.1909027

Design of some novel functionalized thiophene, thieno[2,3-b]thiophene, thiopyran and thiopyrano[2,3-b]thiopyran bearing phosphonate groups was described in one-pot through simple two steps. The methodology depended on the reaction of three-component of chloroacetyl chloride with triethyl phosphite in the presence of sodium 2,2-dicyanoethene-1,1-bis(thiolate) or sodium (2,2-dicyano-1-methylthioethen-1-yl)thiolate in a certain sequence.

Full text of DOI:10.1080/17415993.2021.1909027

Journal of Sulfur Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gsrp20
A convenient one-pot synthesis of novel
functionalized thiophene, thieno[2,3-b] thiophene,
thiopyran, and thiopyrano[2,3-b]thiopyran bearing
phosphonate groups
Tarik E. Ali & Mohammed A. Assiri
To cite this article: Tarik E. Ali & Mohammed A. Assiri (2021): A convenient one-pot synthesis of
novel functionalized thiophene, thieno[2,3-b] thiophene, thiopyran, and thiopyrano[2,3-b]thiopyran
bearing phosphonate groups, Journal of Sulfur Chemistry, DOI: 10.1080/17415993.2021.1909027
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JOURNAL OF SULFUR CHEMISTRY
https://doi.org/10.1080/17415993.2021.1909027
A convenient one-pot synthesis of novel functionalized
thiophene, thieno[2,3-b] thiophene, thiopyran, and
thiopyrano[2,3-b]thiopyran bearing phosphonate groups
Tarik E. Alia,b and Mohammed A. Assiria
aDepartment of Chemistry, Faculty of Science, King Khalid University, Abha, Saudi Arabia; bDepartment of
Chemistry, Faculty of Education, Ain Shams University, Cairo, Egypt
ABSTRACT
ARTICLE HISTORY
Received 1 February 2021
Accepted 19 March 2021
Design of some novel functionalized thiophene, thieno[2,3-b]
thiophene, thiopyran and thiopyrano[2,3-b]thiopyran bearing phos-
phonate groups was described in one-pot through simple two steps.
The methodology depended on the reaction of three-component
of chloroacetyl chloride with triethyl phosphite in the presence of
sodium 2,2-dicyanoethene-1,1-bis(thiolate) or sodium (2,2-dicyano-
1-methylthioethen-1-yl)thiolate in a certain sequence.
KEYWORDS
Synthesis; one-pot;
thiophene; thiopyran;
phosphonate
1. Introduction
Sulfur-containing heterocyclic compounds have a broad range of biological and pharmaco-
logical activities [1]. Thiophene and thiopyran compounds as classes of sulfur-containing
heterocycles are rapidly becoming important classes of therapeutic agents and are likely
to replace many existing pharmaceuticals in the near future [2]. They are reported to pos-
sess variable pharmaceutical applications such as anti-inflammatory [3], antifungal [4,5],
anticancer [6,7] and antimicrobial [8,9] agents. Substituted thiophenes and thiopyrans
and their derivatives are known since the 1950s. One of the most recent synthetic path-
ways for their preparation is based on the cyclisation of ketene dithioacetals, obtained
from carbon disulfide in basic media [10–13]. The intermediates of ketene dithioacetal
disodium salt are reacted generally with the methylene active halides in order to obtain
CONTACT Tarik E. Ali
tarik_elsayed1975@yahoo.com; tismail@kku.edu.sa
© 2021 Informa UK Limited, trading as Taylor & Francis Group

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T. E. ALI AND M. A. ASSIRI
thiophenes and thiopyrans [14–16]. On the other hand, Acyl phosphonate is a useful mem-
ber of the class of organophosphorus compounds that can be used as a reagent to access
P-atom containing organic structures. Having a phosphonate group in the structure may
enhance the biological activity of a parent structure [17,18]. Acyl phosphonates are used
in many reactions and they act as electrophiles and easily react with electron-rich reagents
[19]. In continuation of our work in the development of expected bioactive phosphorus
compounds [20–24], we herein describe the synthesis of novel and expected biologically
active phosphonate-containing thiophenes and thiopyrans. To the best of our knowledge,
there has been no report available on the synthesis of thiophenes and thiopyrans bearing
phosphonate groups, which were synthesized in the present study.
2. Results and discussion
2.1. Chemistry
In this paper, and as a consequence of our previous work, on the simple synthesis of
heterocyclic compounds bearing phosphonate groups of biological interest [25,26], we
investigated a novel efficient protocol that was developed for the construction of function-
alized thiophene, thieno[2,3-b]thiophene, thiopyran and thiopyrano[2,3-b]thiopyran via
three-component reaction in different sequences in refluxing tetrahydrofuran. The starting
materials sodium 2,2-dicyanoethene-1,1-bis(thiolate) (1) [27] and sodium (2,2-dicyano-
1-methylthioethen-1-yl)thiolate (2) [28] were prepared according to the reported methods
in the literature (Figure 1).
Firstly, one-pot three-component condensation of sodium 1-cyano-2-methyl-
thioethylene-2-thiolate (2), chloroacetyl chloride and triethyl phosphite in a cer-
tain sequence afforded diethyl[(3-amino-4-cyano-5-methylthio)thiophene-2-carbonyl]
phosphonate (3) (Figure 1). Thus, heating of triethyl phosphite with chloroacetyl chlo-
ride for 3 h at 150°C formed the intermediate A [29]. When compound 2 was added
to the intermediate A and stirred in THF for one hour at room temperature gave
the nonisolable intermediate B which underwent cyclization by increasing the tem-
perature to 50°C in the presence of triethylamine to isolate diethyl[3-amino-4-cyano-
5-methylthiothiophene-2-carbonyl]phosphonate (3) (Figure 2). In the same manner,
tetraethyl[3,4-diaminothieno[2,3-b]thiophene-2,5-dicarbonyl]bis(phosphonate) (4) was
constructed in using a one-pot three-component reaction. Therefore, the intermediate
A was stirred with half equimolar amount of sodium 2,2-dicyanoethene-1,1-bis(thiolate)
(1) in THF for one hour at room temperature, followed by heating for 3 h at 50°C in the
presence of triethylamine to isolate the target product 4 as shown in Figure 2.
Figure 1. The preparation of starting materials 1 and 2.

JOURNAL OF SULFUR CHEMISTRY
3
Figure 2. The reaction of chloroacetyl chloride with triethyl phosphite then with substrates 1 and 2.
Using the same protocol, the prepared sodium 1-cyano-2-methylthioethylene-
2-thiolate (2) reacted with an equimolar amount of chloroacetyl chloride in THF at room
temperature for 1 h to give the nonisolable chloroacetyl derivative D. Then, triethyl phos-
phite was added to the previous mixture and stirred at 60−70°C for 3 h, followed by the
addition of a few drops of triethylamine to isolate diethyl(4-amino-5-cyano-6-methylthio-
2-oxo-2H-thiopyran-3-yl) phosphonate (5) in good yield (Figure 3).
Finally, sodium 2,2-dicyanoethene-1,1-bis(thiolate) (1) was stirred with two-fold equiv-
alents of chloroacetyl chloride in THF at room temperature for 1 h to give the intermediate
D. Adding of triethyl phosphite then heating under reflux at 60−70°C for 3 h generated the

4
T. E. ALI AND M. A. ASSIRI
Figure 3. The reaction of chloroacetyl chloride with substrate 2 then with triethyl phosphite.
intermediate H that underwent cyclization by th help of triethylamine after another 3 h at
the same temperature to yield the interesting system 6 in moderate yield (Figure 4).
2.2. Spectral characterization
The structures of all synthesized compounds 3−6 were deduced by IR, NMR and MS
spectral and elemental analysis. The IR spectra of compounds 3 and 5 displayed impor-
tant absorption bands at 3385−3102 (NH2), 2257−2225 (CN), 1680−1706 (C=O),
1234−1147 (P =O) and 1004−1020 (P−O−C) cm−1. The 1H-NMR spectra of products 3
and 5 exhibited singlets in the region δ 2.98−2.92 ppm due to the methylsulfanyl protons.
The NH2 protons in product 3 resonated as two singlets at δ 7.04 and 7.06 ppm while the
same group also resonated as one singlet at δ 6.41 ppm in product 5. The diethyl phospho-
nate protons in both products were displayed at δ 1.03−0.77 (CH3) and 4.01−3.42 (OCH2).
Moreover, their 13C-NMR spectra exhibited the characteristic carbon atoms MeS, CN,
CH3 and OCH2 in the regions δ 16.5−19.7, 114.9−112.2, 16.7−14.4 and 61.9−57.7 ppm,
respectively. The carbon atom of the C =O group in compound 3 resonated as a doublet at
δ 184.2 with coupling constant 252 Hz, while the carbon atom C−3 in product 5 appeared
as a doublet at δ 105.1 ppm with coupling constant 236 Hz [30]. The presence of phospho-
nate groups in both products was confirmed by 31P-NMR spectra that showed peaks at δ
23.07 and 26.32 ppm, respectively [31].
Infrared spectra of both compounds 4 and 6 showed new absorption bands for the NH2
groups at 3385−3167 cm−1 and so endorsed the presence of C=O groups at 1667 and 1668
cm−1, respectively. Their 1H-NMR spectra showed two characteristic signals at δ 9.20 and
9.22 for NH2 protons in product 4 and also two singlets at δ 5.79 and 5.97 ppm for the two
NH2 groups in product 6 [32]. The ethoxy protons in both products appeared in the regions

JOURNAL OF SULFUR CHEMISTRY
5
Figure 4. The reaction of chloroacetyl chloride with substrate 1 then with triethyl phosphite.
δ 1.03−1.15 (t, J = 6.8 Hz, CH3) and 3.52−3.69 (m, OCH2) ppm. Furthermore, the
13C-NMR spectrum of structure 4 revealed signals at δ 16.9, 17.6 (2 CH3), 58.1, 58.9 (2
OCH2) and 190.9 (d, JPC = 253 Hz, 2 C=O), while compound 6 exhibited specific car-
bon atoms at δ 15.1, 15.8 (2 CH3), 57.7, 58.7 (2 OCH2), 103.2 (d, JPC = 228 Hz, C−3,6)
and 189.0 (C=O). The 31P-NMR spectra of compounds 4 and 6 appeared at δ 22.51 and
24.55 ppm, respectively, as expected. Furthermore, their mass spectral data confirmed the
proposed structures.
3. Conclusion
A facile route was used to synthesize novel functionalized thiophene, thieno[2,3-b] thio-
phene, thiopyran and thiopyrano[2,3-b]thiopyran bearing phosphonates. The simple and
efficient one-pot three-component approach and the catalyst-free and mild reaction con-
ditions make the present methodology a good synthetic procedure. We hope that this

6
T. E. ALI AND M. A. ASSIRI
approach may be of value to others seeking novel synthetic fragments with unique
properties for medicinal chemistry.
4. Experimental
4.1. General remarks
The melting points were measured on a digital Stuart SMP-3 apparatus in an open capillary
tube. Infrared spectra were measured on FT-IR spectrophotometer (Nicolet iS10) using
KBr disks. The NMR spectra were recorded on a Bruker 400 MHz instrument in DMSO
using TMS as an internal standard. Mass spectra were recorded on direct probe controller
inlet part to single quadropole mass analyzer in (Thermo Scientific GCMS). Elemental
microanalysis was performed on Perkin-Elmer 2400II at the Chemical War department,
Ministry of Defense, Egypt. The purity of the synthesized compounds was checked by thin
layer chromatography (TLC) and elemental microanalysis.
4.2. Synthesis of diethyl(3-amino-4-cyano-5-methylsulfanylthiophene-2-carbonyl)
phosphonate (3)
A mixture of triethyl phosphite (2.5 mmol, 0.41 ml) and chloroacetyl chloride (3 mmol,
0.24 ml) was heated under reflux at 150°C for 3 h. The excess materials were removed
under pressure. A solution of compound 2 (2.5 mmol, 0.44 g) in THF (10 ml) was added
and stirred for 1 h at room temperature followed by adding a few drops of triethylamine
and heated at 50°C for 3 h. The mixture was concentrated under pressure. The formed
solid was filtered off, washed with water and crystallized from methanol to give a beige
solid in 81% yield, mp 143−145°C. IR (KBr), (νmax, cm−1): 3341, 3184 (NH2), 2976,
2922 (C−Haliph), 2257 (CN), 1680 (C=O), 1615 (C=C), 1234 (P =O), 1004 (P−O−C).
1H-NMR (400 MHz, DMSO-d6): 0.77 (t, 3H, J = 6.8 Hz, CH3), 1.03 (t, 3H, J = 6.8 Hz,
CH3), 2.98 (s, 3H, SCH3), 3.98−4.01 (m, 4H, 2 OCH2), 7.04, 7.06 (ss, 2H, NH2). 13C-NMR
(100 MHz, DMSO-d6): 14.4 (CH3), 14.8 (CH3), 16.5 (SCH3), 61.4 (OCH2), 61.9 (OCH2),
98.8 (C−4), 107.6 (C−2), 114.9 (C≡N), 152.9 (C−3), 160.9 (C−5), 184.2 (d, JPC =252 Hz,
C=O). 31P-NMR (162 MHz, DMSO-d6): 23.07 ppm. MS (m/z, I %): 334 (M+, 6%). Anal.
Calcd for C11H15N2O4PS2 (334.34): C, 39.52%; H, 4.52%; N, 8.38%; S, 19.18%. Found: C,
39.34%; H, 4.41%; N, 8.19%; S, 18.99%.
4.3. Synthesis of tetraethyl[3,4-diaminothieno[2,3-b]thiophene-2,5-dicarbonyl]bis
(phosphonate) (4)
A mixture of triethyl phosphite (5 mmol, 0.82 ml) and chloroacetyl chloride (6 mmol,
0.48 ml) was heated under reflux at 150°C for 3 h. The excess materials were removed
under pressure. A solution of compound 1 (2.5 mmol, 0.46 g) in THF (20 ml) was added
and stirred for 1 h at room temperature followed by adding a few drops of triethylamine
and heated at 50°C for 3 h. The formed solid was filtered off, washed with water and crys-
tallized from dioxane-ethanol (1:2) to give yellow solid in 69% yield, mp 252−253°C.
IR (KBr), (νmax, cm−1): 3385, 3275, 3250, 3167 (NH2), 2981, 2955, 2904 (C−Haliph),
1667 (C=O), 1598 (C=C), 1262 (P =O), 1024 (P−O−C). 1H-NMR (400 MHz,

JOURNAL OF SULFUR CHEMISTRY
7
DMSO-d6): 1.03 (t, 6H, J = 6.8 Hz, 2 CH3), 1.15 (t, 6H, J = 7.2 Hz, 2 CH3), 3.54−3.69
(m, 8H, 4 OCH2), 9.20, 9.22 (ss, 2H, NH2). 13C-NMR (100 MHz, DMSO-d6): 16.9 (2
CH3), 17.6 (2 CH3), 58.1 (2 OCH2), 58.9 (2 OCH2), 108.4 (C−2,5), 125.7 (C−3a), 146.6
(C−6a), 150.8 (C−3,4), 190.9 (d, JPC = 253 Hz, 2 C=O). 31P-NMR (162 MHz, DMSO-
d6): 22.51 ppm. MS (m/z, I %): 498 (M+, 22%). Anal. Calcd for C16H24N2O8P2S2 (498.44):
C, 38.56%; H, 4.85%; N, 5.62%; S, 12.86%. Found: C, 38.41%; H, 4.71%; N, 5.43%; S,
12.72%.
4.4. Synthesis of
diethyl(4-amino-5-cyano-6-methylsulfanyl-2-oxo-2H-thiopyran-3-yl) phosphonate
(5)
A mixture of chloroacetyl chloride (3 mmol, 0.24 ml) and compound 2 (2.5 mmol, 0.44 g)
in THF (15 ml) was stirred for 1 h at room temperature. Triethyl phosphite (2.5 mmol,
0.41 ml) was added to the previous mixture and heated under reflux at 60−70°C for 3 h.
A few drops of triethylamine was added, and the mixture was heated at 60−70°C for
2 h. The mixture was concentrated under pressure. The formed solid was filtered off,
washed with water and crystallized from ethanol to give yellow solid in 72% yield, mp
168−170°C. IR (KBr), (νmax, cm−1): 3385, 3284, 3102 (NH2), 2934, 2893 (C−Haliph), 2225
(C≡N), 1706 (C=O), 1604 (C=C), 1147 (P = O), 1020 (P−O−C). 1H-NMR (400 MHz,
DMSO-d6): 1.03 (t, 6H, J = 6.8 Hz, CH3), 2.92 (s, 3H, SCH3), 3.42 (q, 4H, J = 6.8 Hz,
2 OCH2), 6.41 (s, 2H, NH2). 13C-NMR (100 MHz, DMSO-d6): 16.2 (CH3), 16.7 (CH3),
19.7 (SCH3), 57.7 (OCH2), 58.6 (OCH2), 101.1 (C−5), 105.1 (d, JPC = 236 Hz, C−3),
112.2 (CN), 153.0 (C−4), 158.8 (C−6), 180.0 (C=O).31P-NMR (162 MHz, DMSO-d6):
26.32 ppm. MS (m/z, I %): 334 (M+, 10%). Anal. Calcd for C11H15N2O4PS2 (334.34):
C, 39.52%; H, 4.52%; N, 8.38%; S, 19.18%. Found: C, 39.42%; H, 4.44%; N, 8.21%; S,
19.02%.
4.5. Synthesis of tetraethyl(4,5-diamino-2,7-dioxo-2H,7h-thiopyrano[2,3-
b]thiopyran-3,6-diyl)bis(phosphonate) (6)
A mixture of chloroacetyl chloride (6 mmol, 0.48 ml) and compound 1 (2.5 mmol, 0.46 g)
in THF (5 ml) was stirred for 1 h at room temperature. Triethyl phosphite (5 mmol, 0.82 ml)
was added to the previous mixture and heated under reflux at 60−70°C for 3 h. A few drops
of triethylamine was added, and the mixture was heated at 60−70°C for 2 h. The formed
solid was filtered off, washed with water and crystallized from ethanol to give orange solid
in 75% yield, mp 218−220°C (dec). IR (KBr), (νmax, cm−1): 3385, 3279, 3252, 3167 (NH2),
2984, 2904 (C−Haliph), 1668 (C=O), 1590 (C=C), 1260 (P =O), 1022 (P−O−C). 1H-
NMR (400 MHz, DMSO-d6): 1.03 (t, 6H, J = 6.8 Hz, 2 CH3), 1.15 (t, 6H, J = 7.2 Hz,
2 CH3), 3.52−3.69 (m, 8H, 4 OCH2), 5.79, (s, 2H, NH2), 5.97 (s, 2H, NH2). 13C-NMR
(100 MHz, DMSO-d6): 15.1 (2 CH3), 15.8 (2 CH3), 57.7 (2 OCH2), 58.7 (2 OCH2), 103.2
(d, JPC = 228 Hz, C−3,6), 110.1 (C−4a), 146.6 (C−6a), 158.7 (C−5), 189.0 (2 C=O). 31P-
NMR (162 MHz, DMSO-d6): 24.55 ppm. MS (m/z, I %): 498 (M+, 36%). Anal. Calcd for
C16H24N2O8P2S2 (498.04): C, 38.56%; H, 4.85%; N, 5.62%; S, 12.86%. Found: C, 38.43%;
H, 4.68%; N, 5.47%; S, 12.74%.

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T. E. ALI AND M. A. ASSIRI
Acknowledgements
The authors extend their appreciation to the Deanship of Scientific Research at King Khalid
University for funding this work through a general research project under grant number GRP/1/42.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Funding
This work was supported by King Khalid University [grant number GRP/1/42].
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