Multigram scale synthesis of 3,4- and 3,6-dihydro-2H-thiopyran 1,1-dioxides and features of their NMR spectral behavior

Article abstract of DOI:10.1080/00397911.2018.1486427

A new four-step synthesis of 3,4- and 3,6-dihydro-2H-thiopran-1,1-dioxides from dihydro-2H-thiopyran-3(4H)-one is reported. The title compounds are synthesized starting with oxidation of the ketone with a 30% aqueous solution of hydrogen peroxide in a mixture of AcOH-Ac₂O. The keto group is then reduced by sodium borohydride followed by mesylation and elimination of methanesulfonic acid under basic conditions (pyridine for 3,4-isomer and aqueous NaOH for 3,6-isomer). This sequence is simpler, than previously known methods, uses cheaper and more readily available reagents, and leads to 2H-thiopran-1,1-dioxides on multigram scale with 64% and 74% total yields, respectively. The structure and purity of the compounds were confirmed by 2D NMR and GCMS methods. The proposed method expands the means to access functionalized cyclic sulfones as building blocks in the synthesis of combinatorial libraries of new biologically active compounds.

Full text of DOI:10.1080/00397911.2018.1486427

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: http://www.tandfonline.com/loi/lsyc20
Multigram scale synthesis of 3,4- and 3,6-
dihydro-2H-thiopyran 1,1-dioxides and features of
their NMR spectral behavior
Roman M. Chabanenko, Svitlana Yu. Mykolenko, Eugene K. Kozirev & Vitalii
A. Palchykov
To cite this article: Roman M. Chabanenko, Svitlana Yu. Mykolenko, Eugene K. Kozirev &
Vitalii A. Palchykov (2018): Multigram scale synthesis of 3,4- and 3,6-dihydro-2H-thiopyran
1,1-dioxides and features of their NMR spectral behavior, Synthetic Communications, DOI:
10.1080/00397911.2018.1486427
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https://doi.org/10.1080/00397911.2018.1486427
Multigram scale synthesis of 3,4- and 3,6-dihydro-2H-
thiopyran 1,1-dioxides and features of their NMR
spectral behavior
Roman M. Chabanenkoa, Svitlana Yu. Mykolenkob, Eugene K. Kozireva, and
Vitalii A. Palchykova
aDepartment of Organic Chemistry, Oles Honchar Dnipro National University, Dnipro, Ukraine;
bDepartment of Chemistry, Dnipro State University of Agriculture and Economics, Dnipro, Ukraine
ABSTRACT
ARTICLE HISTORY
Received 19 May 2018
A new four-step synthesis of 3,4- and 3,6-dihydro-2H-thiopran-1,1-
dioxides from dihydro-2H-thiopyran-3(4H)-one is reported. The title
compounds are synthesized starting with oxidation of the ketone
with a 30% aqueous solution of hydrogen peroxide in a mixture of
AcOH-Ac2O. The keto group is then reduced by sodium borohydride
followed by mesylation and elimination of methanesulfonic acid
under basic conditions (pyridine for 3,4-isomer and aqueous NaOH
for 3,6-isomer). This sequence is simpler, than previously known
methods, uses cheaper and more readily available reagents, and
leads to 2H-thiopran-1,1-dioxides on multigram scale with 64% and
74% total yields, respectively. The structure and purity of the com-
pounds were confirmed by 2D NMR and GCMS methods. The pro-
posed method expands the means to access functionalized cyclic
sulfones as building blocks in the synthesis of combinatorial libraries
of new biologically active compounds.
KEYWORDS
2D NMR; cyclic
sulfones; oxidation;
reduction; thiopyrans
GRAPHICAL ABSTRACT
Introduction
The cyclic sulfone motif is present in a large number of bioactive molecules and found
broad application in organic synthesis.[1–4] The aim of this paper is the development of
more practical method for the synthesis of 3,4- and 3,6-dihydro-2-thiopyran-1,1-diox-
ides 1 and 2, which can be used as building blocks for the synthesis of plant growth
regulators, herbicides, pesticides, pharmaceutical products, and drug-like compounds.
CONTACT Vitalii A. Palchykov
palchikoff82@gmail.com
Department of Organic Chemistry, Oles Honchar Dnipro
National University, 72 Gagarina Av., Dnipro 49010, Ukraine.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2018 Taylor & Francis

2
R. CHABANENKO ET AL.
Depending on the substitution pattern of the core thiopyran ring, this class of com-
pounds has demonstrated a diverse range of biological activities ranging from
anti-inflammatory and antiviral to ATP-sensitive potassium channel (KATP) openers
(e.g. compounds 3–5).[5–7] Antiglaucoma agent Dorzolamide 6 and diuretic Metikran 7
even became marked drugs (Scheme 1).[8]
Dihydrothiopyran dioxides 1 and 2 were previously obtained from dihydro-
2H-thiopyran-3(4H)-one 8 in four steps with total yields of 35 and 40%, respectively
(Scheme 2).[9] Besides, it was shown that sulfone 1 can be isomerized into 2 under basic
conditions. Following this method,[9] ketone 8 is reduced by large excess of aluminum
isopropoxide, and the resulting alcohol is then brominated by phosphorus tribromide
(described yield is 74%, but in our hands it did not exceed 50% at three fold repeat).
Thiopyran ring is further oxidized to thiopyran dioxide by peroxybenzoic acid (usage of
Scheme 1. Structures of 3,4- and 3,6-dihydro-2H-thiopyran 1,1-dioxides 1, 2 and selected thiopyran-
based biologically important compounds 3-7.
Scheme 2. Known methods for the synthesis of 3,4- and 3,6-dihydro-2H-thiopyran 1,1-dioxides 1, 2.

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3
the cheaper hydrogen peroxide gives 49% yield only) followed by elimination of hydro-
gen bromide under basic conditions. The main disadvantage of this protocol is low total
yield of target sulfones 1, 2, reproducibility of some synthetic steps, and usage of caustic,
expensive, and highly toxic reagents (PBr3, PhCO3H). Authors[10,11] proposed alternative
methods for the synthesis of 2 from ketosulfone 9 (total yield after three steps is 57%)
and 1,5-dibromopentane 10 (total yield after four steps is 40%). The least practical route
is the synthesis of compound 2 from 5-brompent-1-ene 11 (total yield is 6% only).[12]
Results and discussion
When developing a more convenient method for the synthesis of 3,4- and 3,6-dihydro-
2-thiopyran-1,1-dioxides 1 and 2, as the first step we performed oxidation of ketone 8
to ketosulfone 12 using the mixture of aq. H2O2-AcOH-Ac2O (method A, see experi-
mental part). m-Chloroperoxybenzoic acid is a slightly worse variant giving the yield of
71% (method B, see experimental part). The second step is reduction of keto-group by
sodium borohydride in methanol. Interaction of the obtained alcohol 13 with mesyl
chloride almost quantitatively gives the corresponding mesylate 14 (the average yield at
each step is at least 90%). Elimination of methanesulfonic acid from mesylate 14 under
basic conditions leads to target sulfones 1, 2 with good yields on decagram scale
(Scheme 3). It is found that the nature of base plays the key role in regioselectivity of
this elimination. The use of NaOH aqueous solution gives D3-isomer 2 exclusively, and
on the other hand, reflux in pyridine leads to D2-isomer 1. The reaction with
triethylamine provides the mixture of isomers 1, 2 which can be easily turned into pure
D3-isomer 2 by the treatment with 5% aqueous solution of NaOH at room temperature
(r.t.) (yield 77%). So, the reported method leads to the target compounds 1, 2 in
decagram scale with total yields of 64% and 74%, respectively.
As another possible variant for the synthesis of sulfone 2, we performed detosylation
of the compound 15 in different conditions. It seems to be more convenient method,
but refluxing in 10% NaOH aqueous solution leads to the starting material only, and
heating with pyridine gives 2 in dramatically low yield of 32% on 9.10 g scale. In this
case, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) gives much better results on NMR scale
(Scheme 4). It was also found that treatment of the resulted sulfone 2 (analytically pure
sample, 1 mmol) with excess of DBU in DCM solution at r.t. for 7 days afforded mix-
ture of isomers 1 and 2 in ratio 5:95% accordingly (GCMS data). This means that
Scheme 3. New scalable method for the synthesis of 3,4- and 3,6-dihydro-2H-thiopyran-1,1-dioxides 1, 2.

4
R. CHABANENKO ET AL.
Scheme 4. An alternative method for the synthesis of sulfone 2.
sulfone 2 is much more thermodynamically favored product than 1. Thus, above-
described methods for the synthesis of 1 and 2 from mesylate 14 are significantly
more effective.
The tosylate 15 was synthesized from commercially available ketone 16 via com-
pounds 17 and 18 or via ketosulfone 9. We failed to obtain ketone 9 by oxidation with
a 30% aqueous solution of hydrogen peroxide (2.1 eq.) in an AcOH or mixture of
AcOH-Ac2O at 0–20 ꢀC (according to 1 H NMR, no desired ketosulfone 9 in crude
product was observed). Ultimately we synthesized product 9 in methanolic solution
using larger excess of hydrogen peroxide and Na2WO4 as the catalyst. Transformation 9
to 15 was achieved as a one-pot two-step procedure without purification of the inter-
mediate alcohol. So, we obtained tosylate 15 from two different routes from ketone 16
in 58 and 34% overall yields as depicted on the Scheme 4.
It is worth noting that NMR spectra for compound 1 published in works[12,13] are com-
pletely different. Sulfone 2 does not have published NMR spectra at all. Therefore, for the
1
13
detailed investigation of spectral behavior of sulfones 1, 2, we measured their , ‘,
COSY, and HSQC spectra (Figures S1–S4, see Supplemental data). Apart from discrepan-
cies in NMR data, mass spectrum for D2-isomer 1 given in works[12] is the same in detail
as our mass spectrum for D3-isomer 2 (Figures S5, see Supplemental data). Consequently,
according to our set of spectral data, authors[12] made an incorrect conclusion regarding
the regioselectivity of the HCl elimination from the molecule of 3-chlorotetrahydro-2H-thi-
opyran-1,1-dioxide by the treatment with DBU. In this case, D3-isomer 2 is formed, but
not D2-isomer 1 stated in papers (Scheme 2). Studying of peculiarities of NMR spectral
behavior of compounds 1, 2 shows the following observations:
(a)  nuclei of unsaturated fragment of D2-isomer 1 have predictably larger chemical
2,3
3,4
shift in relation to similar nuclei  of the compound 2 (Dd 0.63 ppm) and a
2,3
3,4
higher mutual equivalence (Dd  0.05 ppm for 1 and Dd  0.23 ppm for 2);
2,3
(b) since there is no doubt in mutual assignment of protons  in olefin fragment
of compound 1, from COSY spectrum a weak long range interaction of H3 and
H6 (5J3,6), H2 and H4 nuclei W2,4, allylic coupling) are clearly observed, as well
(
3
3
3
3
as many vicinal interactions J2,3, J3,4, J4,5, and J5,6;
(c) according to the COSY spectrum of compound 2, mutual arrangement of nuclei
3,4

is as follows: 3 < 4, that is, nucleus of proton H3, which is localized close
to the electron-withdrawing SO2 group, uncommonly resonates in a stronger

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5
field. Such arrangement correlates well with the logical assumption that
3J2,3>W2,4. Besides, in the COSY spectrum a weak long range interaction of H2
and H5 (5J2,5, homoallylic coupling), H2 and H4 (W2,4, allylic coupling), H2 and
H6 (W2,6), H3 and H5 (W3,5, allylic coupling) nuclei are clearly observed, as well
3
3
3
3
as many vicinal interactions J2,3, J3,4, J4,5 and J5,6;
1
13
6
(4) position of the chemical shift of  and ‘ nuclei in ‘  methylene group of
2
both isomers is rather close: 3.17 ppm for 1 and 3.08 ppm for 2; 50.69 ppm for 1
and 47.43 ppm for 2.
Detailed NMR data obtained in the course of our work will be useful for the identifi-
cation of related sulfone derivatives.
Conclusion
New four-step method for the synthesis of 3,4- and 3,6-dihydro-2-thiopyran-1,1-
dioxides 1 and 2 from dihydro-2H-thiopyran-3(4H)-one 8 has been developed.
According to this method, ketone 8 was oxidized by hydrogen peroxide, and keto group
was then reduced by sodium borohydride followed by mesylation and elimination of
the methanesulfonic acid under basic conditions. The reported method uses readily
available reagents and leads to the target thiopyran-1,1-dioxides 1, 2 in decagram scale
with total yields of 64% and 74%, respectively. Features of the NMR spectral behavior
of the above mentioned compounds allowed to make reliable assignment of the chem-
1
ical shifts of H, 13 C nuclei and to correctly identify D2- and D3-isomers, and related
compounds. The proposed synthetic protocol expands the means to access similar func-
tionalized cyclic sulfones for the elaboration of combinatorial libraries of biologically
active substances.
Experimental
Solvents were dried and distilled immediately prior to use. Melting points were deter-
mined in open capillary tubes and reported uncorrected. 1 H, 13 C, COSY, and HSQC
1
spectra were measured using Bruker spectrometers (400 and 500 MHz for  nuclei) at
r.t. in appropriate solvents. Chemical shifts (d) are reported in parts per million (ppm)
with respect to the solvent residual signal (CDCl3 1H: d ¼ 7.26 ppm, 13C: d ¼ 77.16 ppm;
DMSO-d6 1H: d ¼ 2.50 ppm, 13C: d ¼ 39.52 ppm). Coupling constants (J) are reported
in Hertz (Hz), and multiplicities are given as s (singlet), d (doublet), t (triplet), dd
(doublet of doublets), and m (multiplet). Purity of the synthesized compounds was
checked by the gas chromatography mass spectrometry using Shimadzu GCMS-QP2010
R
instrument: column Restek Rxi-5ms (CrossbondV 5% diphenyl/95% dimethylpolysilox-
ane), length 30 m, diameter 0.25 mm, thickness 0.25 mm, carrier gas helium, flow rate
1 ml/min, injection mode split, injection temperature 250 ꢀC, column temperature
from 50 to 300 ꢀC with gradient 15 ꢀC/min then isothermally at 300 ꢀC for 5 min. Low
resolution mass spectra of compounds 1, 2 were recorded in electron impact
ionization mode (EI) at the energy of 70 eV in the range of m/z 25–400. Thin layer
chromatography (TLC) was performed on Silufol UV-254 plates in ethyl acetate and
its mixtures with hexane. The plates were visualized with potassium permanganate

6
R. CHABANENKO ET AL.
stain. The elemental analysis (C, H, S) was performed using Carlo Erba analyzer.
The analytical results were within 0.4% of the theoretical values. Starting dihydro-
2H-thiopyran-3(4H)-one
8
was synthesized from methyl thioglycolate and
methyl-4-chlorobutyrate as published,[9] and ketone 16 was purchased from
Enamine Ltd.
Typical experimental procedures for the key compounds
3 ,4-Dihydro-2H-thiopyran-1,1-dioxide (1)
The solution of mesylate 14 (27.00 g, 0.118 mol) in dry pyridine (100 mL) was stirred at
120 j‘ in oil bath for 24 hours. After cooling to r.t., water (200 mL) was slowly added
to the reaction mixture with cooling in the ice bath and then concentrated HCl
(ꢁ95 mL) to the hꢁ2. The product was extracted with dichloromethane (4 ꢂ 200 mL).
Water layer was saturated with crystalline sodium chloride, and product was addition-
ally extracted with ethyl acetate (3 ꢂ 100 mL). Combined organic layers were dried over
sodium sulfate and concentrated in vacuo to oily residue which was distilled under vac-
uum at 123–126 j‘ (1.5 mm Hg). Yield of the crude product 12.80 g (82%, purity by
GCMS 89.3%). The product was further purified by recrystallization from 400 ml
mixture of heptane : ethyl acetate (ꢁ3:1) at overcooling to minus 30 j‘. Yield: 11.03 g
(long transparent needles, purity by GCMS 98.0%), mp 46–46.5 j‘ (44–46 j‘[9]),
1
,
Rf 0.21 (ethyl acetate: hexane, 1:1).  NMR (500 MHz, CDCl3) d 6.43 (1 d,
3J2,3 = 11.2 Hz, H-2), 6.38 (1, d, J2,3 = 11.2 Hz, H-3), 3.20–3.14 (2 H, m, H-6),
3
)
2.36–2.30 (4, m, H-4,5). 13 C NMR (100 MHz, CDCl3 d 138.71 (‘-2), 130.10 (‘-3),
50.69 (‘-6), 24.81 (‘-4), 20.72 (‘-5). Mass spectrum (EI, 70eV), m/z (Irel., %):
ꢃ
132 (Π, 18), 103.0 (88), 87.0 (78), 83.1 (71), 67.1 (56), 55.1 (56), 41.1 (65), 39.1 (100).
The same method was used for the synthesis of sulfone 2 from tosylate 15
(66.0 g, 0.217 mol) in dry pyridine (200 mL). Yield 11.0 g of the crude product
(purity by GCMS 82.9%), after recrystallization 9.10 g (purity by GCMS 96.7%,
32% yield).
3 ,6-Dihydro-2H-thiopyran-1,1-dioxide (2)
To an 5% aqueous solution of sodium hydroxide (200 mL), mesylate 14 (27.00 g,
0.118 mol) was added and the reaction mixture stirred at 20 j‘ for 8 hours. The product
was extracted with dichloromethane (4 ꢂ 200 mL). The combined organic layers were
dried over sodium sulfate and concentrated in vacuo to oily residue which was recrystal-
lized from methyl tert-butyl ether (500 mL). Yield: 14.81 g (95%, purity by GCMS
94.5%), mp 67–69 j‘ (68–72 j‘ (cyclohexane),[10] 65–69 j‘[9]), Rf 0.29 (ethyl acetate:
1
hexane, 1:1). The product should be stored at 4 ꢀC!  NMR (500 MHz, CDCl3) d 5.88
3
3
(1, d, J3,4 ¼ 10.7 Hz, H-4), 5.65 (1, d, J3,4 ¼ 10.7 Hz, H-3), 3.66–3.60 (2 H, m, H-2),
3.11–3.05 (2 H, m, H-6), 2.80–2.74 (2, m, H-5). 13 C NMR (75 MHz, CDCl3) d 126.83
(‘-4), 119.42 (‘-3), 50.79 (‘-2), 47.43 (‘-6), 25.80 (‘-5).[12]  NMR (400 MHz,
1
3
3
DMSO-d6) d 5.80 (1, d, J3,4 ¼ 10.7 Hz, H-4), 5.61 (1, d, J3,4 ¼ 10.7 Hz, H-3),
3.71–3.65 (2 H, m, H-2), 3.18–3.12 (2 H, m, H-6), 2.63–2.57 (2, m, H-5). 13C NMR
(100 MHz, DMSO-d6) d 126.21 (‘-4), 119.96 (‘-3), 49.95 (‘-2), 46.46 (‘-6), 25.62

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ꢃ
(‘-5). Mass spectrum (EI, 70eV), m/z (Irel., %): 131.9 (Œ , 1), 68.0 (22), 67.1 (100),
53.0 (24), 39.0 (21), 41.0 (14).
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by the Ministry of Education and Science of Ukraine [grants
0116U001520 and 0116U007412].
ORCID
Vitalii A. Palchykov
http://orcid.org/0000-0003-3748-4566
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