Polymer-supported eosin Y as a reusable photocatalyst for visible light mediated organic transformations

Article abstract of DOI:10.1039/c9nj04064a

A novel polymer-supported recyclable photocatalyst has been developed for visible light mediated oxidation reactions. The organic dye eosin Y was loaded on macroporous commercially available Amberlite IRA 900 chloride resin and exploited as a photocatalyst for visible light mediated oxidation of thioethers to sulfoxides and phenylboronic acids to phenols under open atmospheric air. Varieties of functional groups were well tolerated during oxidation. The catalyst is recyclable for six cycles without significant loss in its efficiency. Furthermore, gram-scale oxidation of sulfides to sulfoxides has been demonstrated to prove the commercial viability of the method.

Full text of DOI:10.1039/c9nj04064a

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Polymer-supported eosin Y as a reusable
photocatalyst for visible light mediated organic
transformations†
Cite this: New J. Chem., 2019,
43, 17974
Arunasalam Sridhar, Rajmohan Rangasamy and Mari Selvaraj
*
A novel polymer-supported recyclable photocatalyst has been developed for visible light mediated
oxidation reactions. The organic dye eosin Y was loaded on macroporous commercially available
Amberlite IRA 900 chloride resin and exploited as a photocatalyst for visible light mediated oxidation of
thioethers to sulfoxides and phenylboronic acids to phenols under open atmospheric air. Varieties of
functional groups were well tolerated during oxidation. The catalyst is recyclable for six cycles without
significant loss in its efficiency. Furthermore, gram-scale oxidation of sulfides to sulfoxides has been
demonstrated to prove the commercial viability of the method.
Received 5th August 2019,
Accepted 22nd October 2019
DOI: 10.1039/c9nj04064a
rsc.li/njc
of oxidizing agents have been developed.9 Most of the reported
methods rely on the use of stoichiometric oxidants such as TBHP,10
Introduction
In recent years, visible light photocatalysis has gained more atten- hydrogen peroxide,11 oxone,12 etc. Thioxanthone derivatives,13
tion in organic synthesis owing to its sustainability, non-toxicity acetylated riboflavin,14 TiO2 sensitized by alizarin red S,15
and ease of handling.1 Transition-metal complexes, such as Ru(II) polymer-supported and layered double hydroxide (LDH) supported
and Ir(III) bipyridyl complexes, have been extensively employed as rose bengal,16 polydimethylsiloxane supported rose bengal via ion-
photocatalysts due to their ease of synthesis, stability at room exchange reaction17 and perylene diimide18 were used as photo-
temperature, and excellent photoredox properties.2 However metal- catalysts for the oxidation of sulfides to sulfoxides. Recently,
based photoredox catalysts suffer from the disadvantages of being oxidative hydroxylation of phenylboronic acids to phenols was
toxic, highly expensive, and difficult to remove, especially in the achieved in the presence of rose bengal under visible light
pharmaceutical industry.3 Recently, organic dyes such as eosin Y, irradiation.19 Despite high efficiency, these protocols are associated
rose bengal, rhodamine B, and fluorescein have been widely used with one or more limitations such as high cost, need for pure
as photocatalysts due to their ability to be involved in single oxygen, tedious synthesis of the catalyst and so on. Moreover, the
electron-transfer (SET) processes with organic substrates upon catalyst is discarded at the end of the task. A method that uses
photoexcitation with visible light.4 Though numerous develop- atmospheric air as an oxidant and a reusable catalyst is highly
ments have been made on visible light mediated organic transfor- desirable. Hence the present study involves the immobilization of
mations, the use of recyclable heterogeneous photocatalysts xanthene dye on a polymer-support and exploring its potential
remains relatively unexplored.5 Macroporous ion exchange resins as a photocatalyst in the oxidative transformations of sulfides
remain a suitable candidate for immobilization of dyes possessing to sulfoxides and phenylboronic acids to phenols.
carboxylate anions.6 This prompted us to develop novel anion-
exchange resin supported xanthene dyes as reusable catalysts for
visible light mediated photocatalytic reactions.
Results and discussion
Sulfoxides and phenols are the most ubiquitous and important
functional groups present in diverse natural products, and phar- Commercially available Amberlite IRA 900 chloride resin was
maceutical compounds.7 Also, these compounds are synthetic chosen as a polymer-support for synthesizing photocatalysts
intermediates for the construction of various organic molecules.8 with xanthene dyes such as eosin Y, rose bengal and rhodamine
Due to such broad utility, a large number of methods and varieties B. The dye eosin Y was immobilized on the polymer-support
through an anion-exchange reaction (Scheme 1). The loading
capacity of the dye on the polymer-support was studied by
varying the amount of dye per gram of the polymer-support in
Department of Chemistry Guru Nanak College (Autonomous), Velachery, Chennai,
600042, Tamil Nadu, India. E-mail: mariselvaraj@yahoo.com
the same volume of water. The maximum loading of eosin Y
was found to be 1.39 mmol per gram of resin (Table 1, entry 6).
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c9nj04064a
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Table 2 Optimization of the reaction conditions for oxidation of sulfides
to sufoxidesa
Entry
Catalyst (mol%)
Solvent
Yieldb (%)
1
2
3
4
5
6
7
8
PSEY (2)
PSEY (3)
PSEY (3)
PSEY (3)
PSEY (3)
PSRB (3)
PSEY (4)
PSEY (3)
PSEY (3)
PSEY (3)
—
Methanol
Methanol
Water
Acetonitrile
Acetonitrile : water (8 : 2)
Acetonitrile : water (8 : 2)
Acetonitrile : water (8 : 2)
Acetonitrile : water (8 : 2)
Acetonitrile : water (8 : 2)
Acetonitrile : water (8 : 2)
Acetonitrile : water (8 : 2)
64
83
38
72
91
66
Scheme 1 Preparation of polymer-supported eosin Y.
Similarly, rose bengal and rhodamine B were immobilized
on the polymer. The polymer-supported eosin Y and rose
bengal were stable at room temperature for at least up to three
months when stored in brown bottles. However, rhodamine B
was not suitable for immobilization since it immediately leaches
out in aqueous reaction medium.
90
68c
91d
NRe
NR
9
10
11
a
Reaction conditions: reactant (1 mmol), solvent (3 mL), 3 W green
To explore the photocatalytic ability of the polymer-supported
dye, oxidation of thioanisole was chosen as a model reaction.
Initially, thioanisole (1 mmol) in methanol (2 mL) was irradiated
using 3 W green LED lamps in the presence of polymer-supported
eosin Y (2 mol%, Table 1, entry 6) at room temperature under
open air for 6 h. Despite the formation of the expected product
methylsulfinylbenzene, leaching of the dye was additionally
observed, which may be due to heavy loading of the dye. Hence,
we tried the reaction with the polymer containing a lesser amount
of dye. To our delight, the leaching was suppressed to large extent
when 0.296 g of eosin Y (0.046 mmol) immobilized per gram of
polymer resin was used as a photocatalyst (Table 1, entry 3). The
isolated product methylsulfinylbenzene was purified to remove
the residual dye and the yield was found to be 64% (Table 2,
entry 1). Further, when 3 mol% of the catalyst was used, the
yield increased drastically to 83% (entry 2). To optimize the
product yield, oxidation reactions were carried out in different
solvents such as methanol, water, acetonitrile and a mixture of
acetonitrile : water (8 : 2) (entries 2 to 5). Among the screened
solvents acetonitrile : water (8 : 2) was found to be the most
suitable solvent for the reaction, producing the desired product
in 91% yield (entry 5). Relatively lower yields were obtained
when polymer-supported rose bengal (PSRB) was used as a
photocatalyst (entry 6). Only 68% of the product was obtained
when the reaction was conducted under a 3 W blue LED (entry 8).
No significant change in yield or time was observed when the
reaction was carried out under an oxygen atmosphere (entry 9).
b
c
d
LED, open air, 6 h. Isolated yield. A 3 W blue LED was used. Under
an oxygen atmosphere. Without light. PSEY = polymer-supported
eosin Y. PSRB = polymer-supported rose bengal. NR = no reaction.
e
No transformation was observed when the reaction was carried
out in the dark or without the catalyst (entries 10 and 11).
With the established optimum conditions, the substrate scope
of various thioethers for the selective oxidation was explored and
the results are summarized in Table 3. Both phenyl ring bearing
electron donating groups such as p-methyl and p-methoxy and
electron withdrawing groups such as p-cyano and p-nitro
thioethers underwent the selective oxidation and gave the corres-
ponding products in moderate to good yields (64–88%, 2b–2e).
Additionally, excellent yields were obtained when the alkyl chain
length of the alkyl aryl sulfides was increased (85–90%, 2f–2h).
Due to the mild reaction conditions, 4-(methylthio)benzaldehyde
smoothly underwent the selective oxidation of sulfide to sulfoxide
without affecting the more reactive aldehyde functional group
(88%, 2i). To further expand the scope of the substrates,
halogen substituted sulfides were examined. 4-Bromo and
4-chloro thioethers gave the corresponding products in good
yields, which provide the possibility for further functionaliza-
tion (90–93%, 2j–2k). Slightly lesser yields were obtained when
o-substituted sulfides such as 2,6-dichloro, 2-iodo and diphenyl
sulfide were used, perhaps due to the ortho effect (63–74%,
2l–2n). A sulfide containing a naphthyl ring instead of phenyl
also afforded the desired sulfoxide in good yield (78%, 2o).
Slightly higher yields were obtained when the reactions were
performed using simple Na2eosinY (72–81%, 2l–2n).
Table 1 Immobilization study of eosin Y on Amberlite IRA 900 chloride
Encouraged by the results of the oxidation of sulfides by the
newly developed photocatalyst, oxidation studies were carried
out with phenylboronic acid (1 mmol) irradiated using a 14 W
resin
Amount of
eosin Y in the
filtrate (mg)
Amount of eosin Y
immobilized per gram
S. no.
Eosin Y (mg)
of resin mg (mmol) gÀ1 household compact fluorescent lamp in the presence of polymer-
supported eosin Y (3 mol%) as a photocatalyst and triethylamine
1
2
3
4
5
6
100
200
300
400
500
1
3
6
10
13
36
99 (0.14)
(1 mmol) as a sacrificial electron donor in ethanol. Fortunately,
the desired product phenol was isolated in 53% yield and it was
improved to 58% when the catalyst loading was increased to
5 mol% (Table 4, entries 1 and 2). The maximum yield of 76%
197 (0.28)
294 (0.42)
390 (0.56)
487 (0.70)
964 (1.39)
1000
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Table 3 Substrate scope of various thioethersa
Table 4 Optimization of the reaction conditions for the oxidative hydro-
xylation of phenyl boronic acids to phenolsa
Catalyst
Entry (mol%) Base (equiv.)
Solvent (mL)
Yieldb (%)
1
2
3
4
5
6
7
8
PSEY (3) TEA (1)
PSEY (5) TEA (1)
PSEY (5) TEA (1)
PSEY (5) TEA (1)
PSEY (5) TEA (1)
PSEY (5) TEA (1)
PSEY (5) DIPEA
PSEY (5) DABCO (1)
Ethanol
Ethanol
Acetonitrile
DMF
53
58
43
27
NR
Water
Acetonitrile : water (8 : 2) 76
Acetonitrile : water (8 : 2) 53
Acetonitrile : water (8 : 2) 21
9
PSEY (5) Amberlyst A21 (2) Acetonitrile : water (8 : 2) 16
10
11
12
PSRB (5) TEA (1)
PSEY (5) TEA (1)
PSEY (5) TEA (1)
Acetonitrile : water (8 : 2) 61
Acetonitrile : water (8 : 2) NRc
Acetonitrile : water (8 : 2) 68d
a
Reaction conditions: reactant 3 (1 mmol), solvent (3 mL), 14 W compact
b
c
d
fluorescent lamp, open air, 36 h. Isolated yield. Without light. A 12 W
green LED was used. PSEY = polymer-supported eosin Y. PSRB = polymer-
supported rose bengal. NR = no reaction.
Table 5 Substrate scope of various phenylboronic acidsa
a
Isolated yield. b Reaction was performed using simple Na2eosin Y (3 mol%).
was observed when a mixture of acetonitrile : water (8: 2) was
used (entry 6). Among the several bases such as triethylamine,
DIPEA, DABCO and Amberlyst A 21 screened for the reaction
triethylamine proved to be the best choice (entry 6). However,
polymer-supported rose bengal gave only a lesser yield (entry 10).
The reaction did not proceed in the absence of light (entry 11).
With the optimized conditions, oxidation of several boronic
acids was carried out with the eosin Y loaded catalyst and the
results are presented in Table 5. Boronic acids bearing either an
electron-donating group such as 2-ethyl, 3,4-dimethyl, and
2-methoxy or an electron withdrawing group such as 4-amido
and 4-cyano on the benzene ring were able to undergo this
transformation smoothly and provided the corresponding products
in moderate to good yields and no significant electronic effects
were observed (4b–4f). Compounds containing easily oxidizable
a
Isolated yield.
aldehyde functional groups such as 2-formyl and 4-formyl- such as 3-bromo, 2-fluoro-3-methoxy, and 2-fluoro-4-benzyl-
phenylboronic acids also yielded the corresponding phenols oxyphenylboronic acids could afford the corresponding phenols
in moderate yields (4g and 4h). Halogen containing substrates in good yields (4i–4k). Gratifyingly, heterocyclic compound
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Table
6
Oxidation of thioethers to sulfoxides using the polymer-
supported [Ru(bpy)3]2+ complexa
Scheme 2 Gram-scale reaction.
a
Isolated yield.
Fig. 1 Recyclability of the polymer-supported eosin Y.
benzofuran-5-ylboronic could also deliver the desired product
in moderate yield (4l). Notably, compounds with fused aromatic
rings like 2-naphthalene and 1-pyrene boronic acids were
successfully subjected to this reaction system, also producing
the respective phenols in admirable yields (4m and 4n).
A gram-scale reaction was performed with 1a to investigate the
versatility of the protocol. The product 2a was obtained in 86% yield
with no significant loss compared to the pilot scale (Scheme 2).
To investigate the recyclability and reusability of the photo-
catalyst, after the completion of oxidation of methyl phenyl sulfide
the catalyst was separated by simple filtration, washed with water
and acetonitrile and dried and reused in subsequent oxidation
reactions. The results suggested that the catalyst can be reusable
up to six cycles without a significant loss in its efficiency (Fig. 1).
Similarly, we immobilized the [Ru(bpy)3]2+ complex, a
Fig. 2 Recyclability of the polymer-supported [Ru(bpy)3]2+ complex.
electron from thioether 1 and sensitizes oxygen to form the
superoxide radical anion (O2 À). This superoxide radical anion
ꢀ
combines with thioether radical cation A to form the desired
sulfoxide 2. In a similar manner, the generated superoxide
radical anion transforms phenylboronic acid 3 to phenol 4.
Experimental
Drying of Amberlite IRA 900 chloride resin
transition-metal based photocatalyst, on the polymer-support and About 10 g of wet commercially available Amberlite IRA 900
its catalytic efficiency was explored for the oxidation of thioethers chloride resin was soaked in acetonitrile (50 mL) for 30 minutes,
to sulfoxides. Preliminary optimization studies suggested that blue filtered and then immersed in methanol (20 mL) for 30 minutes
LED lights gave a higher yield (87%) than green LEDs (63%). Use of and filtered. The isolated resin was dried using a rotary evapora-
molecular oxygen provided better yields than atmospheric air. An tor at 50 1C until it flows freely and then dried in a hot air oven at
acetonitrile : water (8 : 2) mixture accelerated the yield in comparison 50 1C for 1 hour.
with other solvents like methanol, ethanol and acetonitrile. How-
ever, this reaction required a longer time for transformation when
Preparation of polymer-supported eosin Y
compared with the reaction using polymer-supported eosin Y as a 1 g of dried Amberlite IRA 900 chloride resin was gently stirred
photocatalyst. Phenyl ring bearing electron donating groups and with an aqueous solution of Na2eosin Y (0.3 g in 40 mL water,
electron withdrawing groups both afforded the desired products 0.43 mmol) for 4 h. The catalyst was filtered and the filtrate was
without significant electronic effects (Table 6).
carefully collected in a 250 mL standard flask. The catalyst
Oxidation of methyl phenyl sulphide was chosen as a model obtained was sonicated using an ultrasonic bath cleaner for
reaction to test the recyclability of the catalyst. The results suggested 5 minutes in 10 mL of deionized water and the solution is
that the newly prepared polymer-supported [Ru(bpy)3]2+ complex collected in the same standard flask. This process was repeated
can be reused for at least four cycles without much loss in its 5 times to remove the residual dye. Then the catalyst was dried
activity (Fig. 2).
using a rotary evaporator and kept in a vacuum desiccator
Based on the previous reports, a possible mechanism was overnight. The solution collected was made up to 250 mL in a
proposed (Scheme 3). Initially, on absorption of visible light, standard flask to analyze the loading capacity of the dye using a
polymer-supported eosin Y (PSEY) gets excited, picks up an UV-vis spectrophotometer.
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Scheme 3 Proposed mechanism.
General procedure for the synthesis of sulfoxides
taken in a round bottom flask containing 2 mL of acetonitrile :
water (8 : 2) mixture. Then the flask was fitted with a balloon
filled with oxygen and the reaction mixture was irradiated using
blue LEDs (2 Â 6 W) for 12 h. Then, the catalyst was separated
by filtration, washed with water and acetone and reused.
A mixture of thioether 1 (1 mmol) and polymer-supported
eosin Y (3 mol%) was taken in an oven dried round bottom
flask containing 3 mL of acetonitrile : water (8 : 2) and irradiated
with green LEDs (2 Â 3 W) at room temperature under an open
air atmosphere. The completion of the photoreaction was
monitored by TLC. After completion, the catalyst was separated
by filtration and the reaction mixture was extracted with ethyl
acetate (3 Â 5 mL) and dried over anhydrous Na2SO4. The
solvent was removed under reduced pressure and the residue
was purified by column chromatography on silica gel (eluent:
hexanes/ethyl acetate 10/1 - 5/1 - 1/1) to afford the product 2.
Conclusions
In summary, we have developed novel polymer-supported eosin
Y as a reusable catalyst for visible light mediated reactions. The
efficiency of the catalyst was demonstrated in the oxidation of
thioethers to sulfoxides and phenylboronic acids to phenols in
the presence of energy efficient and cheap visible light sources.
A range of aromatic sulfoxides and phenols were obtained in good
General procedure for the synthesis of phenols
A mixture of phenylboronic acid 3 (1 mmol), trimethylamine to excellent yields. The reaction requires only atmospheric air as
(0.5 mmol) and polymer-supported eosin Y (5 mol%) was an oxidant and the catalyst is recyclable up to six cycles. Thus, a
taken in an oven dried round bottom flask containing 3 mL highly efficient, eco-friendly photocatalytic methodology for the
of acetonitrile : water (8 : 2) and irradiated with a compact fluo- selective oxidation of thioethers to sulfoxides and phenylboronic
rescent lamp (14 W) at room temperature under an open air acids to phenols has been developed. Similarly, [Ru(bpy)3]2+
atmosphere. The completion of the photoreaction was monitored was also immobilized on a polymer-support and used for the
by TLC. After completion, the catalyst was separated by filtration and oxidation of thioethers to sulfoxides. Further applications of
the reaction mixture was extracted with ethyl acetate (3 Â 5 mL) the photocatalysts are being studied in our laboratory.
and dried over anhydrous Na2SO4. The solvent was removed
under reduced pressure and the residue was purified by column
chromatography using a hexanes and ethyl acetate mixture (9: 1)
Conflicts of interest
as the eluent to afford the product 4.
There are no conflicts to declare.
Preparation of the polymer-supported ruthenium complex
1 g of resin (Indion 190 cation exchange resin) was stirred in a Acknowledgements
solution of [Ru(bpy)3]Cl2Á6H2O (0.02 g) in deionized water
We thank the Council of Scientific and Industrial Research (CSIR),
(50 mL) for one hour. Then, the resin was filtered, washed
New Delhi, India for the award of a Senior Research Fellowship.
thoroughly with water and acetone and dried in a vacuum.
Oxidation of thioethers to sulphoxides using the
polymer-supported ruthenium complex
Notes and references
0.075 g of 4-(methylsulfinyl)benzonitrile (0.5 mmol) and the
polymer-supported ruthenium complex (0.3 g, 2 mol%) were
1 (a) N. A. Romero and D. A. Nicewicz, Chem. Rev., 2016, 116,
10075–10166; (b) L. Marzo, S. K. Pagire, O. Reiser and
17978 | New J. Chem., 2019, 43, 17974--17979 This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019

View Article Online
Paper
B. Konig, Angew. Chem., Int. Ed., 2018, 57, 10034–10072;
NJC
¨
9 (a) D. Zhao, N. Wu, S. Zhang, P. Xi, X. Su, J. Lan and J. You,
Angew. Chem., Int. Ed., 2009, 48, 8729–8732; (b) Y. Liu, S. Liu and
Y. Xiao, Beilstein J. Org. Chem., 2017, 13, 589–611; (c) H.-Y. Xie,
L.-S. Han, S. Huang, X. Lei, Y. Cheng, W. Zhao, H. Sun, X. Wen
and Q.-L. Xu, J. Org. Chem., 2017, 82, 5236–5241; (d) K. Matsui,
T. Ishigami, T. Yamaguchi, E. Yamaguchi, N. Tada, T. Miura
and A. Itoh, Synlett, 2014, 2613–2616; (e) S. P. Pitre, C. D.
McTiernan, H. Ismaili and J. C. Scaiano, J. Am. Chem. Soc.,
¨
(c) B. Konig, Eur. J. Org. Chem., 2017, 1979–1981.
2 (a) C. K. Prier, D. A. Rankic and D. W. C. MacMillan, Chem. Rev.,
2013, 113, 5322–5363; (b) M. H. Shaw, J. Twilton and
D. W. C. MacMillan, J. Org. Chem., 2016, 81, 6898–6926;
(c) J. M. R. Narayanam and C. R. J. Stephenson, Chem. Soc.
Rev., 2011, 40, 102–113.
3 (a) A. K. Yadav and L. D. S. Yadav, Tetrahedron Lett., 2014,
55, 2065–2069; (b) A. K. Singh, R. Chawla and L. D. S. Yadav,
Tetrahedron Lett., 2015, 56, 653–656.
ˇ
´
2013, 135, 13286–13289; ( f ) S. Liao, I. Coric, Q. Wang and
B. List, J. Am. Chem. Soc., 2012, 134, 10765–10768.
¨
4 (a) D. P. Hari and B. Konig, Chem. Commun., 2014, 50, 10 (a) L. Zhao, H. Zhang and Y. Wang, J. Org. Chem., 2016, 81,
6688–6699; (b) V. Srivastava and P. P. Singh, RSC Adv., 2017,
7, 31377–31392.
5 (a) C. Su, R. Tandiana, B. Tian, A. Sengupta, W. Tang, J. Su
and K. P. Loh, ACS Catal., 2016, 6, 3594–3599; (b) J. Chen,
J. Cen, X. Xu and X. Li, Catal. Sci. Technol., 2016, 6,
349–362.
6 (a) A. Sridhar, S. Swarnalakshmi and M. Selvaraj, Synlett,
2016, 1344–1348; (b) S. Gazi and R. Ananthakrishnan, Appl.
Catal., B, 2011, 105, 317–325.
129–136; (b) S. Guo, L. Lu and H. Cai, Synlett, 2013, 1712–1714.
11 (a) B. Karimi, M. Ghoreishi-Nezhad and J. H. Clark, Org.
Lett., 2005, 7, 625–628; (b) M. M. Khodaei, K. Bahrami and
A. Karimi, Synthesis, 2008, 1682–1684; (c) A. Gogoi and
U. Bora, Synlett, 2012, 1079–1081.
12 (a) G. A. Molander and L. N. Cavalcanti, J. Org. Chem., 2011,
76, 623–630; (b) R. Kupwade, S. Khot, U. Lad, U. Desai and
P. Wadgaonkar, Res. Chem. Intermed., 2017, 43, 6875–6888.
13 C. Ye, Y. Zhang, A. Ding, Y. Hu and H. Guo, Sci. Rep., 2018,
8, 2205.
7 (a) Z. Rappoport, The chemistry of phenols, John Wiley &
´
´
¨
Sons, 2004; (b) N. Goncharov, A. N. Orekhov, N. Voitenko, 14 J. Dad’ova, E. Svobodova, M. Sikorski, B. Konig and
A. Ukolov, R. Jenkins and P. Avdonin, in Nutraceuticals, ed. R. Cibulka, ChemCatChem, 2012, 4, 620–623.
R. C. Gupta, Academic Press, Boston, 2016, pp. 555–568; 15 H. Hao, Z. Wang, J.-L. Shi, X. Li and X. Lang, ChemCatChem,
(c) C. Schaefer, Drugs During Pregnancy and Lactation, Academic 2018, 10, 4545–4554.
Press, Oxford, 2nd edn, 2007, pp. 708–737; (d) S. Patai, 16 (a) X. Gu, X. Li, Y. Chai, Q. Yang, P. Li and Y. Yao, Green
Z. Rappoport and C. Stirling, The chemistry of sulfones and
sulfoxides, John Wiley & Sons, 1988.
8 (a) M. C. Carreno, Chem. Rev., 1995, 95, 1717–1760;
Chem., 2013, 15, 357–361; (b) Y. Huang, Z. Xin, W. Yao,
Q. Hu, Z. Li, L. Xiao, B. Yang and J. Zhang, Chem. Commun.,
2018, 54, 13587–13590.
(b) S. Quideau, D. Deffieux, C. Douat-Casassus and 17 X. Li, Y. Li, Y. Huang, T. Zhang, Y. Liu, B. Yang, C. He,
´
L. Pouysegu, Angew. Chem., Int. Ed., 2011, 50, 586–621;
X. Zhou and J. Zhang, Green Chem., 2017, 19, 2925–2930.
(c) X. Huang and N. Maulide, J. Am. Chem. Soc., 2011, 133, 18 Y. Gao, H. Xu, S. Zhang, Y. Zhang, C. Tang and W. Fan, Org.
´
8510–8513; (d) R. Fernandez de la Pradilla, M. Tortosa,
E. Castellanos, A. Viso and R. Baile, J. Org. Chem., 2010, 19 W.-Z. Weng, H. Liang and B. Zhang, Org. Lett., 2018, 20,
75, 1517–1533. 4979–4983.
Biomol. Chem., 2019, 17, 7144–7149.
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 17974--17979 | 17979