A straightforward synthesis of 5-sulfonamidomethyl substituted 4,7-dihydroazolo[1,5-a]pyrimidines

Article abstract of DOI:10.1080/00397911.2020.1821224

4,7-Dihydroazolo[1,5-a]pyrimidin-5-ylmethanesulfonamides are side-products of the three-component Biginelli-like reaction of aminoazoles, aldehydes and N,N-dialkyl-2-ketomethanesulfonamides. Herein, we report a straightforward synthesis of 5-sulfonamidomethyl substituted 4,7-dihydroazolo[1,5-a]pyrimidines by a two-component condensation of aminoazoles and N,N-dialkyl(cinnamoyl)methanesulfonamides in DMF at reflux. The starting N,N-dialkyl-2-ketomethanesulfonamides can be obtained by either lithiation of N,N-dialkylmethanesulfonamides and reaction with aldehydes followed by oxidation of the resulting alcohols or by Claisen condensation of N,N-dialkylmethanesulfonamides with the corresponding esters. The chemical structures of all synthesized compounds are supported by ¹H and ¹³C NMR-spectroscopy, mass spectrometry and elemental analysis.

Full text of DOI:10.1080/00397911.2020.1821224

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/lsyc20
A straightforward synthesis of 5-
sulfonamidomethyl substituted 4,7-
dihydroazolo[1,5-a]pyrimidines
Elena H. Shvets , Anastasiya V. Pidvorotnya , Olesia G. Kulyk , Alexander V.
Mazepa & Maksim A. Kolosov
To cite this article: Elena H. Shvets , Anastasiya V. Pidvorotnya , Olesia G. Kulyk ,
Alexander V. Mazepa & Maksim A. Kolosov (2020): A straightforward synthesis of 5-
sulfonamidomethyl substituted 4,7-dihydroazolo[1,5-a]pyrimidines, Synthetic Communications, DOI:
10.1080/00397911.2020.1821224
To link to this article: https://doi.org/10.1080/00397911.2020.1821224
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SYNTHETIC COMMUNICATIONSV
https://doi.org/10.1080/00397911.2020.1821224
A straightforward synthesis of 5-sulfonamidomethyl
substituted 4,7-dihydroazolo[1,5-a]pyrimidines
Elena H. Shvetsa , Anastasiya V. Pidvorotnyaa, Olesia G. Kulyka
Alexander V. Mazepab, and Maksim A. Kolosova
,
b
aSchool of Chemistry, V. N. Karazin Kharkiv National University, Kharkiv, Ukraine; A.V. Bogatsky
Physico-Chemical Institute of the NAS of Ukraine, Odesa, Ukraine
ABSTRACT
ARTICLE HISTORY
Received 11 July 2020
4,7-Dihydroazolo[1,5-a]pyrimidin-5-ylmethanesulfonamides are side-
products of the three-component Biginelli-like reaction of aminoa-
zoles, aldehydes and N,N-dialkyl-2-ketomethanesulfonamides. Herein,
we report a straightforward synthesis of 5-sulfonamidomethyl substi-
tuted 4,7-dihydroazolo[1,5-a]pyrimidines by a two-component con-
KEYWORDS
Biginelli-like reaction;
Claisen condensation;
4,7-dihydroazolo[1,5-a]pyri-
midines; 2-ketosulfona-
mides; N,N-
densation
of
aminoazoles
and
N,N-dialkyl(cinnamoyl)
methanesulfonamides in DMF at reflux. The starting N,N-dialkyl-2-
ketomethanesulfonamides can be obtained by either lithiation of
N,N-dialkylmethanesulfonamides and reaction with aldehydes fol-
lowed by oxidation of the resulting alcohols or by Claisen condensa-
tion of N,N-dialkylmethanesulfonamides with the corresponding
esters. The chemical structures of all synthesized compounds are
dialkylmethanesulfonamides
1
supported by H and 13C NMR-spectroscopy, mass spectrometry and
elemental analysis.
GRAPHICAL ABSTRACT
Introduction
The sulfonamide functional group is a valuable bioactive moiety of many natural and
synthetic compounds with a broad spectrum of biological activities including antibacter-
ial, diuretic, antihypertensive, antifungal, anticancer, antiviral, and antiepileptic.[1] As a
consequence of the high pharmacological importance of sulfonamides, considerable
attention has been paid to the development of novel approaches for their preparation.[2]
Among a variety of sulfonamide derivatives, the synthesis of sulfonamide containing
4,7-dihydroazolo[1,5-a]pyrimidines and 1,4-dihydropyridines is of particular interest.[3]
Indeed, partially hydrogenated pyrimidines,[4] pyridines[5] and azolopyrimidines[6]
CONTACT Olesia G. Kulyk
olesia.g.kulyk@karazin.ua; Maksim A. Kolosov
kolosov@karazin.ua
School of
Chemistry, V. N. Karazin Kharkiv National University, Kharkiv 61022, Ukraine.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2020 Taylor & Francis Group, LLC

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E. H. SHVETS ET AL.
Scheme 1. Formation of the mixture in the reaction of 3-amino-1,2,4-triazole, aldehydes and 1-(piper-
idin-1-ylsulfonyl)propan-2-one.
Scheme 2. Retrosynthetic analysis of 4,7-dihydro[1,2,4]triazolo[1,5-a]pyrimidine-5-ylmethanesulfona-
mides of type 2.
represent an important class of pharmaceutically relevant heterocycles possessing a wide
range of therapeutic applications.
Recently, we reported for the first time the synthesis of 6-sulfonamide substituted
4,7-dihydro[1,2,4]triazolo[1,5-a]pyrimidines (DTPMs) of type 1 by a Biginelli-like three-
component condensation of 1-(1-piperidinylsulfonyl)acetones, aromatic aldehydes and
3-amino-1,2,4-triazole in DMF (Scheme 1).[3b] However, the modest yields of the target
products (18–42%) prompted us for further investigation of this reaction. We found
that along with the desired compounds the formation of side-products was occurred.
The structure of side-products – 5-sulfonamidomethyl substituted DTPMs of type 2,
1
was determined based on H NMR spectroscopic analysis of the reaction mixtures. As a
continuation of our research and in order to verify the feasibility of our assumption,
herein we decided to investigate the straightforward synthesis of 5-sulfonamidomethyl
substituted DTPMs of type 2. Notably, to date no information has been disclosed on
the synthesis of azolo[1,5-a]pyrimidine derivatives, containing sulfonamidomethyl sub-
stituent in the position 5 of heterocycle.
Results and discussion
Heterocyclization of aminoazoles with a,b-unsaturated ketones is the most widely used
approach leading to azolo[1,5-a]pyrimidine derivatives.[7] Hence, the strategy toward
the synthesis of 2 can be rationalized by the retrosynthetic sequence depicted in
Scheme 2. The formation of 5-sulfonamidomethyl substituted DTPM ring proceed via a
two-component condensation of 3-amino-1,2,4-triazole with N,N-dialkyl(cinnamoyl)
methanesulfonamides.
For the synthesis of (cinnamoyl)methanesulfonamides, the previously reported strate-
gy,[3b] i.e., initial preparation of 2-hydroxysulfonamides followed by its oxidation using
Jones reagent,[8] was applied. Accordingly, lithiation of 1-(methylsulfonyl)piperidine 3
(1 equiv., in THF) at ꢀ15 ꢁC using n-BuLi (1.03 equiv., 2.5 M solution in hexane) fol-
lowed by treatment of the resulting lithium salt with a solution of cinnamaldehyde

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3
Scheme 3. Synthesis of 1-(piperidin-1-ylsulfonyl)-4-phenylbut-3-en-2-one 5a.
Scheme 4. Synthesis of N,N-dialkyl-2-ketomethanesulfonamides 5 via Claisen condensation.
(1.05 equiv., in THF) afforded alcohol 4 in 98% yield (Scheme 3). However, the attempt
to oxidize 4 using Jones reagent turned to failure, resulting in the formation of complex
1
mixture as determined by TLC and H NMR spectroscopy. This was attributed to the
probable occurrence of undesired rearrangements due to the presence of allyl fragment
in the substrate. To circumvent this limitation, the oxidation using MnO2 was carried
out to obtain desired ketone 5a with 71% yield.
Furthermore, we explored the alternative one-step approach toward 2-ketosulfona-
mides involving the Claisen condensation of 3 with various esters (Scheme 4). To this
end, 1-(methylsulfonyl)piperidine 3 and ethyl benzoate which is not able to give self-
condensation products were taken as model substrates to carry out the optimization of
the reaction conditions. We found that proton abstraction from 3 (1 equiv.) with NaH
(1.2 equiv.) in a mixture of THF–cyclohexane (1:1) at 0 ꢁC under argon followed by
heating the resulting sodium salt with ethyl benzoate (1.5 equiv.) at reflux gave 2-keto-
sulfonamide 5b in 38% yield. Aiming to enhance the yield of 5b, further investigation
on ratio of the reactants was conducted. The best result was achieved when a solution
of 1-(methylsulfonyl)piperidine 3 (1 equiv.) and ethyl benzoate (1.5 equiv.) in THF was
added to a vigorously stirred suspension of NaH (1.7 equiv.) in a mixture of
THF–cyclohexane (1:1) at 0 ꢁC under argon followed by heating the resulting mixture at
reflux for 20 h. Subsequent work-up and recrystallization of the crude product from
EtOH produced 5b in 79% yield (Scheme 4). To our delight, the Claisen condensation
proceeded smoothly when methyl cinnamate and methyl 3-(4-chlorophenyl)acrylate
were employed affording desired 2-ketosulfonamides 5a and 5c in 61% and 58% yields,
respectively.
In addition, the optimized conditions were tested for the preparation of 2-ketosulfo-
namide 5d previously obtained in our group by a two-step protocol.[3b] However, when
ethyl acetate for which proton transfer from the a-carbon is favorable was used, the for-
mation of ethyl acetoacetate along with the target product was observed. To overcome
this, treatment of 3 (1 equiv.) with NaH (1.7 equiv.) in a mixture of THF–cyclohexane
(1:1) at 0 ꢁC for 1 h under argon was followed by reaction of as-formed methanesulfona-
mide carbanion with ethyl acetate (1.1 equiv.) at reflux temperature for 14 h to furnish

4
E. H. SHVETS ET AL.
Scheme 5. Two approaches toward the synthesis of N,N-dimethyl-2-oxopropane-1-sulfonamide 8.
5d in 48% yield. When N,N-dimethylmethanesulfonamide 6 was employed in the con-
densation with ethyl acetate under above conditions, an inseparable mixture of the tar-
get product and ethyl acetoacetate was revealed. Subsequently, the reaction conditions
were evaluated, and we found that a decrease in temperature led to target product 8 in
59% yield (Scheme 5, Path I).
Following the alternative approach which involves the synthesis of 2-hydroxysulfona-
mide 7 and its subsequent oxidation by Jones reagent, 2-ketosulfonamide 8 was
obtained in 60% yield over these two steps (Scheme 5, Path II).
The chemical structures of 2-hydroxysulfonamides 4 and 7 as well as 2-ketosulfona-
1
mides 5 and 8 were confirmed by H and 13C NMR-spectroscopy, mass spectrometry
and elemental analysis. Surprisingly, in the EI MS spectra of compounds 5a–c no
molecular ion peaks appeared. Even in the EI MS spectrum of 4 where molecular ion
peak showed up, it had very low abundance (4%). Compared with EI ionization method
which usually lacks the capability to provide the molecular ion peaks, the FAB method
is a soft ionization technique which readily provides a molecular ion.[9] Indeed, FAB
MS spectra of 4 and 5a–c clearly displayed expected molecular ion peaks with high
abundance along with the matrix liquid related peaks (3-nitrobenzyl alcohol).
Noteworthy, the fragmentation appeared in FAB MS spectra of 4 and 5a–c was similar
to, though not exactly the same as that observed in their EI MS spectra (for details see
Supplementary Information).
Finally, target 5-sulfonamidomethyl substituted 4,7-dihydroazolo[1,5-a]pyrimidines 2
were obtained by heating of 2-ketosulfonamides 5a or 5c with the corresponding ami-
noazole in DMF at reflux under argon for 2 h (Scheme 6).
Since depending on the applied conditions various reaction products can be obtained
by the condensation of aminoazoles with a,b-unsaturated ketones,[7d,10] it is worth not-
ing that the heating of starting (cinnamoyl)methanesulfonamides with aminoazoles in
DMF leads only to azolo[1,5-a]pyrimidine derivatives.
1
Having in hand pure 5-sulfonamidomethyl DTPM 2a, we compared its H NMR
1
spectrum with the H NMR spectra of pure 6-sulfonamide substituted DTPM 1a and
1
the mixture of both products previously obtained (Figure 1). In contrast to the H
1
NMR spectrum of 2a, where a singlet of N(4)H at 9.76 ppm is observed, in the H
NMR spectrum of 1a a singlet of N(4)H is shifted to 11.01 ppm due to the effective

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5
Scheme 6. Synthesis of 4,7-dihydroazolo[1,5-a]pyrimidine-5-sulfonamides 2.
Figure 1. 1H NMR spectra (500 MHz, DMSO-d6) of (a) mixture of 6-sulfonamide substituted DTPM 1a
and 5-sulfonamidomethyl substituted DTPM 2a; (b) pure 1a; (c) pure 2a.
conjugation of the nitrogen atom with the sulfonamide group. Further comparison of
1
the H NMR spectra of compounds 1a and 2a revealed crucial differences in the charac-
ter of hydrogen resonances corresponding to the substituents in positions 5, 6 and 7.
Specifically, 5-sulfonamidomethyl group of 2a is characterized by multiplet of AB sys-
tem around 4.04–3.91 ppm relating to the diastereotopic protons of CH2-group and two
multiplets around 3.21–3.05 and 1.56–1.36 ppm assigned to the piperidinyl protons,
while C(6)H and C(7)H exhibited a multiplet around 4.96–4.87 ppm and a doublet at
1
6.19 ppm (3J ¼ 3.0 Hz), respectively. On the other hand, the H NMR spectrum of 1a
presented one singlet at 2.36 ppm that refers to the protons of C(5)CH3-group, two
multiplets around 3.01–2.87 and 1.43–1.32 ppm corresponding to the piperidinyl pro-
tons and one singlet of C(7)H at 6.17 ppm. In addition, both products showed a singlet
1
of C(2)H at 7.67 and 7.62 ppm for 1a and 2a, respectively. Hence, with the help of H
and 13C NMR spectroscopy together with mass spectrometry, the structure of 2a was
established.
Interestingly, when the mixture of 3-amino-1,2,4-triazole, N,N-dimethyl-2-oxopro-
pane-1-sulfonamide 8 and 4-chlorobenzadehyde was heated at reflux in DMF under
argon for 2 h, only product 9 was isolated in 58% yield (Scheme 7).

6
E. H. SHVETS ET AL.
Scheme 7. Three-component reaction of 3-amino-1,2,4-triazole, N,N-dimethyl-2-oxopropane-1-sulfona-
mide 8 and 4-chlorobenzadehyde.
Scheme 8. Plausible pathway for 5-sulfonamidomethyl DTPMs formation via three-component
condensation.
On the basis of our findings and literature data, the plausible pathway for 5-sulfona-
midomethyl DTPMs formation by three-component condensation of 3-amino-1,2,4-tri-
azole, aldehydes and N,N-dialkyl-2-ketomethanesulfonamides is outlined in Scheme 8.
The nucleophilic addition of 2-ketosulfonamides to an aldehyde with the subsequent
loss of H2O furnishes the a,b-unsaturated intermediate. Such behavior of a methyl
group in 2-ketosulfonamides possessing more reactive methylene group is attributed to
the steric hindrance of the latter. Subsequent intermolecular nucleophilic attacks of exo-
cyclic NH2 and endocyclic NH of 3-amino-1,2,4-triazole at electron-deficient carbonyl
carbon and double bond of cinnamoylsulfonamide, respectively, provides the target 5-
sulfonamidomethyl DTPMs.
Noteworthy, the similar behavior of CH3-group as the CH-acidic center instead of
the more reactive CH2-group was previously reported for a three-component condensa-
tion of urea, aromatic aldehydes and 2-ketosulfones, resulting in the formation of
unusual Hantzsch dihydropyridines.[11]
Conclusion
In summary, the chemical structure of 5-sulfonamidomethyl 4,7-dihydroazolo[1,5-a]pyr-
imidines – side-products of the three-component Biginelli-like reaction of aminoazoles,
aldehydes and N,N-dialkyl-2-ketomethanesulfonamides, was confirmed via their inde-
pendent synthesis by condensation of aminoazoles with N,N-dialkyl(cinnamoyl)metha-
nesulfonamides. Two practical approaches were successfully applied for the
preparation of starting N,N-dialkyl-2-ketomethanesulfonamides, i.e., Claisen condensa-
tion of N,N-dialkylmethanesulfonamides with the corresponding esters as well as reac-
tion of lithiated N,N-dialkylmethanesulfonamides with aldehydes followed by the
oxidation of 2-hydroxysulfonamides.

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7
Experimental part
General procedure for the synthesis of 2-ketosulfonamides (5a–c)
To a vigorously stirred suspension of NaH (60% dispersion in mineral oil, 1.70 g,
42.5 mmol) in a mixture of THF-cyclohexane (1:1, 30 mL), a solution of 1-(methylsulfo-
nyl)piperidine 3 (4.10 g, 25.1 mmol) and corresponding ester (37.7 mmol) in THF
(5 mL) was added at 0 ꢁC under argon. The resulting mixture was heated at reflux for
20 h. A sodium salt of the product precipitated. After cooling to r.t., the solid was fil-
tered off, washed with THF–cyclohexane (1:1, 3 ꢂ 10 mL) and then dissolved in water
(100 mL). The pH of the aqueous phase was adjusted to ca. 7 by the addition of acetic
acid. The following work-up was carried out in two ways. For compounds 5b and 5c,
the aqueous phase was extracted by CH2Cl2 (3 ꢂ 40 mL), and the extract dried over
Na2SO4, filtered and concentrated under reduced pressure. For compound 5a, the pre-
cipitate formed in the aqueous phase was filtered off, washed with water (3 ꢂ 10 mL)
and dried under air.
General procedure for the synthesis of 7-aryl-5-((piperidin-1-ylsulfonyl)methyl)-
4,7-dihydroazolo[1,5-a]pyrimidines (2a–c)
A solution of 2-ketosulfonamide 5a or 5c (2.3 mmol) and the corresponding aminoazole
(2.3 mmol) in DMF (2.5 mL) was heated at reflux for 2 h. After cooling to r.t., EtOH
(5 mL) was added and the reaction mixture additionally refluxed for 15 min. After cool-
ing the formed precipitate was filtered off, washed with EtOH (3 ꢂ 2 mL) and dried
under air to give target product.
7-(4-Chlorophenyl)-5-((piperidin-1-ylsulfonyl)methyl)-4,7-dihydro[1,2,4]triazolo[1,5-
a]pyrimidine (2a)
Prepared from 5c (754 mg), and 3-amino-1,2,4-triazole (193 mg). White solid (380 mg,
1
42%), m.p. 262–267ꢁ‘ (with decomposition). H NMR (500 MHz, DMSO-d6) d 9.76
(1H, s, NH), 7.62 (1H, s, C(2)H), 7.43 (2H, d, J ¼ 8.3 Hz, ArH), 7.23 (2H, d, J ¼ 8.3 Hz,
ArH), 6.19 (1H, d, J ¼ 3.0 Hz, C(7)H), 4.96–4.87 (1H, m, C(6)H), 4.04–3.91 (2H, m,
CH2), 3.21–3.05 (4H, m, N(CH2)2), 1.56–1.36 (6, m, (‘2)3); 13C NMR (126 MHz,
DMSO-d6) d 149.7, 148.8, 140.5, 132.6, 128.5 (two signals are overlapping), 126.2, 100.5,
58.7, 51.6, 46.2, 25.2, 23.1; m/z (EI, 70 eV): 395 (Œ(37Cl)þ, 17), 393 (Œ(35Cl)þ, 45), 282
(55), 246 (73), 209 (32), 134 (15), 84 (100). Anal. Calcd. for C17H20ClN5O2S (393.89):
C, 51.84; H, 5.12; N, 17.78; S, 8.14%. Found: C, 51.91; H, 5.20; N, 17.61; S, 8.27%.
Supplemental data associated with this article (Full experimental detail, characteristics
1
for all new compounds, copies of H and 13C NMR, LRMS spectral data) can be found
via the “Supplementary Content” section of this article’s webpage.
Acknowledgments
We thank V.I. Musatov (STC “Institute for Single Crystals” NAS of Ukraine, Kharkiv, Ukraine)
for spectroscopic measurements.

8
E. H. SHVETS ET AL.
Funding
The research was supported by Grant 0118U002025 of Ministry of Education and Science of
Ukraine and by Grants 811H/10–18, 811H/6–19 of V. N. Karazin Kharkiv National University.
ORCID
Elena H. Shvets
Olesia G. Kulyk
Maksim A. Kolosov
http://orcid.org/0000-0003-4791-2114
http://orcid.org/0000-0003-0303-6941
http://orcid.org/0000-0002-6714-0513
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