Facile Synthesis of β-Keto Sulfones Employing Fenton's Reagent in DMSO

Article abstract of DOI:10.1055/s-0036-1589151

A new facile method for the synthesis of β-keto sulfones employing xanthates, DMSO, and Fenton's reagent is described. The reaction proceeds under very mild conditions providing a cost-effective straightforward approach to various β-keto sulfones in high yields.

Full text of DOI:10.1055/s-0036-1589151

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© Georg Thieme Verlag Stuttgart · New York
2018, 29, A–E
letter
A
en
P. N. Chalikidi et al.
Letter
Synlett
Facile Synthesis of β-Keto Sulfones Employing Fenton’s Reagent in
DMSO
Petrakis N. Chalikidia
Maxim G. Uchuskinb
H2O2
FeSO4•7H2O
O
O
S
O
O
S
Igor V. Trushkovc
Vladimir T. Abaev*a
Olga V. Serdyuk*d
S
OEt
+
R
5 °C to r.t., 3 h
Me
Me
R
Me
S
O
11 examples
72–86% yields
a K. L. Khetagurov North Ossetian State University, Vatutina St. 46,
362025 Vladikavkaz, Russian Federation
hampazero@mail.ru
b Perm State University, Bukireva 15, 614990 Perm, Russian Federa-
tion
c Faculty of Science, RUDN University, Miklukho-Maklaya 6, 117198
Moscow, Russian Federation
d Department of Chemistry and Pharmacy, University of Erlangen-
Nuremberg, Henkestrasse 42, 91054 Erlangen, Germany
oserduke@mail.ru
Dedicated to the memory of Professor Alexander V. Butin, colleague and close friend
Received: 26.10.2017
Accepted after revision: 16.11.2017
Published online: 02.01.2018
Not surprisingly, the formation of β-keto sulfones 3 as side
products has been observed upon the radical reaction of
phenacyl xanthates 1 with furans 2 in dimethyl sulfoxide
(Scheme 1).19 Indeed, dimethyl sulfoxide is known to be a
source of the methyl sulfonyl group (-SO2Me).20
DOI: 10.1055/s-0036-1589151; Art ID: st-2017-d0789-l
Abstract A new facile method for the synthesis of β-keto sulfones em-
ploying xanthates, DMSO, and Fenton’s reagent is described. The reac-
tion proceeds under very mild conditions providing a cost-effective
straightforward approach to various β-keto sulfones in high yields.
DMSO, H2O2
FeSO4·7H2O
O
O
S
OEt
+
Key words β-keto sulfones, sulfones, xanthates, dimethyl sulfoxide,
Fenton’s reagent, radical reaction
Ar
Alk
O
Alk
Ar
5 °C to r.t.
2.5 h
O
Ar
O
S
1
2 (47–67%)
O
O
2-Oxoalkyl sulfones (β-keto sulfones) are known to be ver-
satile building blocks commonly used in organic synthesis.1
Bearing a carbonyl group at the β-position to the sulfonyl
group and an active methylene fragment, they provide
excellent possibilities for the preparation of such targets as
chalcones and flavanones,2 2-amino-4H-pyrans,3 acetylenes,4
quinolines,5 substituted benzenes,6 furans,7 triazoles,8 and
others.9 Moreover, several examples are known to possess
fungicidal,10 antimicrobial,11 and other types of biological
activity.12
The most studied approaches to β-keto sulfones include
alkylation of sulfinates with α-halo ketones,13 acylation of
methyl sulfones,14 and oxidation of β-keto sulfides.15Addi-
tionally, syntheses of β-keto sulfones employing straight-
forward functionalization of alkenes,16 alkynes,17 and
methyl ketones18 have been described recently. The advan-
tages of the reported methods are the prevention of addi-
tional derivatization of starting compounds, as well as con-
tribution to the development of more environmentally be-
nign chemical syntheses. However, some drawbacks, such
as moderate yields, poor regioselectivity, and limited scope
of reaction, still remain. Mostly, these methods start with
the generation of a sulfonyl radical that then reacts further.
+
S
Ar
Me
Ar
O
O
3 (22–62%)
4 (5–7%)
Scheme 1 Reaction of xanthates 1 with furans under Fenton condi-
tions
Our studies have demonstrated that, without a furan
substrate, the reaction of xanthates 1 with dimethyl sulfox-
ide provided β-keto sulfones 3 in high yields along with 1,4-
diketones 4 as minor products. Herein, we describe a new
facile method for the synthesis of β-keto sulfones employ-
ing Fenton’s reagent under very mild conditions.
Initially, we studied the model reaction of xanthate
1a with dimethyl sulfoxide in the presence of iron(II) sul-
fate and 34% hydrogen peroxide (Table 1). The best yield
of the product 3a (65%) was achieved when 20 mmol of
hydrogen peroxide were slowly added to a cooled reac-
tion mixture containing 10 mmol of substrate 1a and 10
mmol of FeSO4·7Н2О (Table 1, entry 6). Thereby, the most
optimal ratio of 1/FeSO4·7Н2О/Н2О2 was found to be
1:1:2.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E

B
P. N. Chalikidi et al.
Letter
Synlett
The use of 12 mmol or 15 mmol of FeSO4·7Н2О and the
same amount of Н2О2 (20 mmol) did not improve the yield
of the product 3a (Table 1, entries 7 and 8). Moreover, using
30 mmol of Н2О2, the compound 3a was isolated in an even
lower yield (Table 1, entry 10). When the reaction
was performed in the presence of 15 mmol or 20 mmol
of FeSO4·7Н2О and 30 mmol of Н2О2, decomposition of
the product led to a further decrease the reaction out-
come. These experiments produced 3a in 52% and 48%
yield, respectively (Table 1, entries 11 and 12).
sulfinic acid and subsequent oxidation of intermediate B
gives the desired product 3 according to Path B. Finally, the
reaction of A with DMSO followed by the transformation of
sulfoxide C according to Path C is also possible, but seems
to be less likely.
Fe(II)
H2O2
OH
(i)
Fe(III)OH
+
+
OH
O
O
O
S
O
S
+ MeH
(ii)
+
Me
S
Me
Me
OH
Me
Me
O
Table 1 Yields of Compounds 3a and 4a in the Model Reaction of 1a
O
(iii)
(iv)
Me
with DMSOa,b
Xt
R
CH2
R
– MeXt
1
A
O
O
S
O
O
O
S
Me
Ph
Me
S
O
O
O
O
O
Fe(III)OH
Me
OH
H2O2
FeSO4·7H2O
3
3
3a (major)
S
S
OEt
O
S
– Fe(II)
– H2O
Me
Path A
R
CH2
Path B
R
Ph
+
+
OH
O
5 °C to r.t.
30 min
A
B
S
Me
Me
Ph
1a
DMSO
– Me
Ph
Path C
O
4a (minor)
O
O
O
O
Fe(III)OH
OH
Me
3
Entry
FeSO4·7Н2О
(mmol)
H2O2
(mmol)
Yield of 3a
(%)
Yield of 4a
(%)
S
S
Me
– Fe(II)
– H2O
R
R
OH
C
B
1
2
5
10
12
15
5
10
10
10
10
20
20
20
20
30
30
30
30
42
48
50
50
45
65
64
65
60
58
52
48
6
7
Scheme 2 Plausible reaction mechanism
3
6
4
6
Probably, all suggested pathways work under the reac-
tion conditions cooperatively. However, the short lifetime
of methyl sulfonyl radicals, and the fact that methyl radi-
cals, required for their generation, are consumed in the re-
action with xanthate 1, led us to propose that Path B is
dominant.21b In this case, accumulation of methylsulfinic
acid in the reaction mixture should promote the forma-
tion of 3. To confirm this, we performed the synthetic
protocol in a stepwise manner. First, a solution of 5 mmol
of FeSO4·7Н2О in 30 mL of DMSO was treated with 10
mmol of H2O2 and the mixture was stirred for 30 min-
utes. Then, 10 mmol of xanthate 1, an additional 5 mmol
of FeSO4·7Н2О, and 10 mmol of H2O2 were added to the re-
action mixture. In accordance with our expectations, fol-
lowing the stepwise protocol allowed compound 3a to be
obtained in higher yield (Table 2, entry 1). For further opti-
mization of the reaction conditions, we studied variations
of the amounts of DMSO, FeSO4·7Н2О, and H2O2 (Table 2,
entries 2–7). The optimal ratio of 1/FeSO4·7Н2О/Н2О2 was
found to be 1:2:4 (Table 2, entry 6). In this case, the β-keto
sulfone 1a was isolated in 86% yield. Further increasing the
amount of FeSO4·7Н2О did not influence the reaction out-
come significantly. Notably, using 30 mmol of FeSO4·7Н2О,
the desired product was obtained in a slightly lower yield
(Table 2, entry 7).
5
4
6
10
12
15
5
9
7
9
8
8
9
8
10
11
12
10
15
20
8
9
10
aWith 10 mmol of xanthate 1a and 30 mL of DMSO.
bIsolated yields after column chromatography.
To optimize the reaction conditions, we considered the
mechanism of the transformation 1→3 (Scheme 2). The
proposed mechanism starts with the generation of a hy-
droxyl radical under Fenton conditions (i). Subsequent reac-
tion with DMSO results in formation of a methyl radical and
methanesulfinic acid, the decomposition of which affords
•
methyl sulfonyl radicals MeSO2 (ii).21 The reaction of xan-
thate 1 with a methyl radical leads to the key intermediate
A (iii). Further transformation of A into the target sulfone 3
can proceed via several pathways, depending on the nature
of the reactive sulfur species. Thus, the recombination of A
with methyl sulfonyl radicals provides the target product 3
via Path A (iv). The transformation of A with methane-
© Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E

C
P. N. Chalikidi et al.
Letter
Synlett
Table 2 Optimization of Reaction Conditions for the Synthesis of β-
Keto Sulfone 3a Using a Stepwise Protocola,b
With optimal reaction conditions established, a variety
of xanthates 1 was evaluated as substrates, and the results
are summarized in Scheme 3. Notably, most of the reac-
tions with xanthates bearing both electron-withdrawing
and electron-donating groups on the aromatic moiety
can be performed in high yields. The only exception was
xanthate 1i, which afforded 2-hydroxy-4-methoxy-
acetophenone (5) in 88% yield. We believe that radical A′
might undergo an intramolecular hydrogen transfer fol-
lowed by formation of phenoxyl radical D. Its subsequent
reduction with Fe(II) would afford 2-hydroxy-4-methoxy-
acetophenone (5). The hydroxyl group acts as an intramo-
lecular inhibitor for the reaction 1→3 in this case.
O
O
S
Ph
Me
O
O
H2O2
3a (major)
FeSO4·7H2O
S
OEt
O
S
Ph
+
+
O
5 °C to r.t., 3 h
S
Me
Me
1a
Ph
Ph
O
4a (minor)
Entry
FeSO4·7Н2О
(mmol)
H2O2
(mmol)
DMSO
(mL)
Yield of 3a Yield of
(%)
4a (%)
The proposed methodology was then applied to the syn-
thesis of heterocyclic β-keto sulfones. Thus, thiophen-2-yl
and furan-2-yl derivatives 3j and 3k were obtained in 72%
and 74% yield, respectively. Moreover, the method permits
the preparation of ethyl 2-(methylsulfonyl)acetate (3l, 78%).
As a further illustration of the utility of the developed
approach, we used commercially available phenacyl ha-
lides 6 and 7 as starting compounds (Scheme 5). The target
β-keto sulfone 3b could be obtained, but in these experi-
ments, the isolated yields of the desired product 3b were
lower in comparison with the transformation of the corre-
sponding xanthate 1b (48% and 59%).
1
2
3
4
5
6
7
10
10
20
30
10
20
30
20
20
20
20
40
40
40
30
40
40
40
40
40
40
70
72
71
70
76
86
84
5
4
4
4
4
3
3
aWith 10 mmol of xanthate 1a.
bIsolated yields after column chromatography.
H2O2
FeSO4·7H2O
O
O
O
S
O
S
S
OEt
+
R
R
Me
Me
Me
5 °C to r.t., 3 h
O
S
3
1
O
O
S
O
O
S
O
O
S
O
O
S
Me
Me
Me
Me
Me
O
O
O
O
Br
Cl
MeO
3a (86%)
3b (85%)
3c (86%)
3d (80%)
O
O
S
O
O
O
O
O
O
S
MeO
MeO
S
MeO
MeO
S
O
O
Me
Me
Me
O
O
O
O
O2N
NO2
3e (86%)
3f (78%)
3g (86%)
3h (76%)
O
O
S
O
O
S
O
O
O
O
S
Me
S
Me
O
Me
O
EtO
Me
O
O
O
S
MeO
OH
3i (-)d
Me
3j (72%)
3k (74%)
3l (78%)
Scheme 3 Substrate scope for the reaction of xanthates 1 with DMSO.a–c aReagents and conditions: 10 mmol of xanthate 1, 20 mmol of FeSO4·7Н2О, 20
mmol of H2O2, 40 mL of DMSO. bIsolated yields after column chromatography. cSide products 4 were formed in very low yield (0–3%), separated by
column chromatography, and are not presented in this scheme. d2-Hydroxy-4-methoxyacetophenone 5 was isolated in 88% yield.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E

D
P. N. Chalikidi et al.
Letter
Synlett
O
O
References and Notes
O
Fe(II) + H2O
Me
– MeXt
CH2
H
CH3
(1) For selected recent reviews on synthesis and application of β-
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Shermolovich, Y. G. J. Sulfur Chem. 2013, 35, 188. (b) Pena, J.;
Moro, R. F.; Markos, I. S.; Diez, D. Curr. Org. Chem. 2014, 18,
2972. (c) Elattar, K. M.; Fekri, A.; Bayoumy, N. M.; Fadda, A. A.
Res. Chem. Intermed. 2017, 43, 4227.
1i
MeO
MeO
O•
A'
D
O
CH3
+ Fe(III)OH
(2) Kumar, A.; Sharma, S.; Tripathi, V. D.; Srivastava, S. Tetrahedron
2010, 66, 9445.
MeO
OH
(3) (a) Macro, J. L.; Fernandez, I.; Khira, N.; Fernandez, P.; Romero,
A. J. Org. Chem. 1995, 60, 6678. (b) Macro, J. L. J. Org. Chem. 1997,
62, 6575.
(4) Ihara, M.; Suzuki, S.; Taniguchi, T.; Tokunaga, Y.; Fukumoto, K.
Tetrahedron 1995, 51, 9873.
5 (88%)
Scheme 4 Transformation of xanthate 1i into 2-hydroxy-4-methoxy-
acetophenone (5)
O
H2O2
FeSO4·7H2O
(5) Swenson, R. E.; Sowin, T. J.; Zhang, H. Q. J. Org. Chem. 2002, 67,
9182.
O
S
Hal
+
5 °C to r.t., 3 h
Me
Me
Me
(6) Chang, M.-Y.; Cheng, Y.-C.; Lu, Y.-J. Org. Lett. 2015, 17, 3142.
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C.-K.; Chen, Y.-H.; Hsu, R.-T.; Chang, M.-Y. Tetrahedron 2017, 73,
46.
Br
6 (Hal = Br)
7 (Hal = I)
Br
O
O
O
S
+
O
O
Br
Br
3b
4b
Hal
Br
I
3b (%)
48
59
4b (%)
5
5
(10) Wolf, W. M. J. Mol. Struct. 1999, 474, 113.
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Chem. 2007, 42, 880.
Scheme 5 Synthesis of β-keto sulfone 3b starting from halides 6 and
7. Reagents and conditions: 10 mmol of 6 or 7, 20 mmol of FeSO4·7Н2О,
20 mmol of H2O2, 40 mL of DMSO. Isolated yields after column chroma-
tography are given.
(12) (a) Xiang, J.; Ipek, M.; Suri, V.; Tam, M.; Xing, Y.; Huang, N.;
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Bioorg. Med. Chem. 2015, 23, 2579.
In conclusion, we have developed a new facile method
for the synthesis of β-keto sulfones employing xanthates
and Fenton’s reagent in DMSO.22 The reaction proceeds un-
(13) For selected examples, see: (a) Vennstra, G. E.; Zwaneburg, B.
Synthesis 1975, 519. (b) Suryakiran, N.; Reddy, T. S.; Ashalatha,
K.; Lakshman, M.; Venkateswarlu, Y. Tetrahedron Lett. 2006,
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dron 2015, 71, 5525. (e) Shin, U. S.; Joo, S.-R.; Kim, S.-H. Bull. Kor.
Chem. Soc. 2016, 37, 1144.
der very mild conditions, providing
a cost-effective
straightforward approach to various β-keto sulfones in high
yields. A plausible mechanism has been proposed for this
transformation. We have also demonstrated that commer-
cially available phenacyl halides can be used as starting
compounds for this reaction.
(14) For selected examples, see: (a) Grosset, S. J.; Dubey, P. K.; Gill, G.
H.; Cameron, S. T.; Gardner, P. A. Can. J. Chem. 1984, 62, 798.
(b) Katritzky, A. R.; Abdel-Fattah, A. A. A.; Wang, M. J. Org. Chem.
2003, 68, 1443. (c) Pospíšil, J.; Sato, H. J. Org. Chem. 2011, 76,
2269. (d) Pospiil, J.; Robiette, R.; Sato, H.; Debrus, K. Org. Biomol.
Chem. 2012, 10, 1225.
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Curtin, N. J.; Echalier, A.; Endicott, J. A.; Hardcastle, I. R.; Newell,
D. R.; Noble, M. E. M.; Wang, L. Z.; Golding, B. T. J. Am. Chem. Soc.
2006, 128, 6012. (b) Bahrami, K.; Khodaei, M. M.; Arabi, M. S. J.
Org. Chem. 2010, 75, 6208. (c) Li, Q.-S.; Li, C.-Y.; Lu, X.; Zhang, H.;
Zhu, H.-L. Eur. J. Med. Chem. 2012, 50, 288.
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Chem. Sci. 2014, 5, 4939. (c) Wei, W.; Wen, J.; Yang, D.; Wu, M.;
You, J.; Wang, H. Org. Biomol. Chem. 2014, 12, 7678.
Funding Information
The authors thank the Russian Foundation for Basic Research (Grant
No. 16-03-00807) for financial support.
)(
Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0036-1589151.
S
u
p
p
ortiInfogrmoaitn
S
u
p
p
ortioInfgrmoaitn
© Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E

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Letter
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(d) Taniguchi, N. J. Org. Chem. 2015, 80, 7797. (e) Yadav, V. K.;
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tion mixture was poured into H2O (30 mL) and extracted with
EtOAc (4 × 50 mL). The combined organic phases were washed
with brine, dried over anhydrous Na2SO4, filtered, and evapo-
rated under reduced pressure. The resulting crude mixture of
products was purified by silica column chromatography using
EtOAc–PE (1:4) as eluents. The yield of compound 3a was 1.71 g
(86%).
Characterization Data of Representative Compounds 3
2-(Methylsulfonyl)-1-phenylethanone (3a)23
(18) Rawat, V. S.; Reddy, P. L. M.; Sreedhar, B. RSC Adv. 2014, 4, 5165.
(19) Chalikidi, P. N.; Nevolina, T. A.; Uchuskin, M. G.; Abaev, V. T.;
Butin, A. V. Chem. Heterocycl. Compd. 2015, 51, 621.
(20) For review on application of DMSO as reagent, see: Wu, X.-F.;
Natteb, K. Adv. Synth. Catal. 2016, 358, 336.
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Chem. Scand. 1970, 24, 3590. (b) Gilbert, B.; Norman, R.; Sealy,
R. J. Chem. Soc., Perkin Trans. 2 1975, 303. (c) Veltwisch, D.;
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(22) Representative Experimental Procedure for the Synthesis of
Compound 3a
Pale yellow solid (1.71 g, isolated yield 86%); mp 107–109 °C
(PE–EtOAc = 2:1), lit. 86–90 °C.23 1H NMR (400 MHz, DMSO-d6):
δ = 8.10–7.97 (m, 2 H), 7.72 (m, 1 H), 7.58 (dd, J = 10.7, 4.9 Hz, 2
H), 5.11 (s, 2 H), 3.16 (s, 3 H) ppm. 13C NMR (100 MHz, DMSO-
d6): δ = 190.59, 136.34, 134.75, 129.50, 129.31, 61.23, 42.51
ppm. ESI-HRMS: m/z calcd for C9H10O3SNa [M + Na]+: 221.0248;
found: 221.0242.
Ethyl 2-(Methylsulfonyl)acetate (3l)24
Colorless oil (1.295 g, isolated yield 78%). 1H NMR (400 MHz,
CDCl3): δ = 4.25 (q, J = 7.1 Hz, 2 H), 3.99 (s, 2 H), 3.12 (s, 3 H),
1.29 (t, J = 7.1 Hz, 3 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
163.10, 62.65, 59.12, 41.62, 13.95 ppm. ESI-HRMS: m/z calcd for
C5H10O3SNa [M + Na]+: 189.0197; found: 189.0189.
(23) Shi, X.; Ren, X.; Ren, Z.; Li, J.; Wang, Y.; Yang, S.; Gu, J.; Gao, Q.;
Huang, G. Eur. J. Org. Chem. 2014, 5083.
34% H2O2 (2 mL, 20 mmol) was added to a cooled solution of
FeSO4·7Н2О (2.78 g, 10 mmol) in DMSO (40 mL), and the
mixture was stirred for 30 min at 5–10 °C. Then, xanthate 1a
(2.4 g, 10 mmol), FeSO4·7Н2О (2.78 g, 10 mmol), and H2O2(2 mL,
20 mmol) were added and the reaction mixture was stirred for
30 min at 5–10 °C and, then, 2 h at r.t. (TLC control). The reac-
(24) Lattanzi, A.; Bonadies, F.; Schiavo, A.; Scettri, A. Tetrahedron:
Asymmetry 1998, 9, 2619.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E