Photoredox-Catalyzed Sulfonylation of O-Acyl Oximes via Iminyl Radicals with the Insertion of Sulfur Dioxide

Article abstract of DOI:10.1021/acs.orglett.9b01323

A multicomponent sulfonylation of O-acyl oximes via iminyl radicals with the insertion of sulfur dioxide under photoredox catalysis is achieved. This multicomponent reaction of O-acyl oximes, potassium metabisulfite, alkenes, and nucleophiles under visible-light irradiation is efficient, giving rise to a range of sulfones in moderate to good yields. A broad reaction scope is presented with good functional group compatibility.

Full text of DOI:10.1021/acs.orglett.9b01323

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Photoredox-Catalyzed Sulfonylation of O‑Acyl Oximes via Iminyl
Radicals with the Insertion of Sulfur Dioxide
Jun Zhang,†,‡ Xiaofang Li,§ Wenlin Xie,§ Shengqing Ye,*,† and Jie Wu*,†,‡
†School of Pharmaceutical and Materials Engineering & Institute for Advanced Studies, Taizhou University, 1139 Shifu Avenue,
Taizhou 318000, China
‡Department of Chemistry, Fudan University, 2005 Songhu Road, Shanghai 200438, China
§School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, China
S
* Supporting Information
ABSTRACT: A multicomponent sulfonylation of O-acyl
oximes via iminyl radicals with the insertion of sulfur dioxide
under photoredox catalysis is achieved. This multicomponent
reaction of O-acyl oximes, potassium metabisulfite, alkenes,
and nucleophiles under visible-light irradiation is efficient,
giving rise to a range of sulfones in moderate to good yields. A
broad reaction scope is presented with good functional group
compatibility.
urrently, sulfonylation with the insertion of sulfur dioxide
Cvia a radical process under mild conditions has attracted
continuous interest.1,2 Many approaches have appeared that
radicals.10a The iminyl radicals were generated via a photo-
reductive strategy from O-acyl oximes under irradiation by
visible light. Guo and co-workers reported the synthesis of
cyanoalkylated heteroarenes through an iron-catalyzed C−H
cyanoalkylation of heteroarenes via C−C bond cleavage of
cyclobutanone oxime esters.10b Inspired by these results and
recent advances with the insertion of sulfur dioxide,1 we
envisioned that sulfur dioxide might react with iminyl radicals
under photoredox catalysis as well.
We hypothesized that a multicomponent sulfonylation of O-
acyl oximes via iminyl radicals with the insertion of sulfur
dioxide under photoredox catalysis would be feasible for the
synthesis of β-substituted sulfones. This proposed multi-
component reaction of O-acyl oximes 1, sulfur dioxide, alkenes
2, and nucleophiles under visible-light irradiation is presented
in Scheme 1. We reasoned that in the presence of
photocatalyst under visible-light irradiation O-acyl oxime 1
would undergo the N−O bond dissociation to provide iminyl
radical intermediate A, which would go through the intra-
molecular C−C bond cleavage leading to a carbon radical B.
This carbon radical B would be trapped by sulfur dioxide to
produce sulfonyl radical C, which would then attack the double
bond of alkene 2 to afford another carbon radical intermediate
D. A subsequent oxidative single-electron transfer (SET) by
the oxidized form of photocatalyst would give rise to a cation
intermediate E. In the presence of base, the nucleophile would
be involved and react with cation E leading to the
corresponding product 3. With this consideration in mind,
we thus started to explore the practicability of this trans-
formation.
3
use the sulfur dioxide surrogates of DABCO·(SO2)2 and
inorganic sulfites4 instead of gaseous sulfur dioxide. Different
radical precursors including aryldiazonium tetrafluoroborates,
aryl halides, diaryliodonium salts, and potassium alkyltrifluor-
oborates have been reported for the generation of carbon
radicals, which would initiate the reaction with the capture of
sulfur dioxide to produce sulfonyl radical intermediates. Thus,
diverse sulfonyl compounds can be efficiently prepared with
the insertion of sulfur dioxide, especially from the cheap and
easily available inorganic sulfites.
The core β-substituted sulfone such as β-alkoxy sulfone can
be found in many biologically active molecules.5 In general,
these sulfones are synthesized through the oxidation of β-
alkoxy sulfides or the alkoxylation of α,β-unsaturated sulfones.6
However, a stoichiometric amount of exogenous additives/
oxidants is required, which limits their applicability in organic
synthesis. Difunctionalization of alkenes through sulfonylation
for the preparation of β-substituted sulfones provides an
alternative route. For example, Lei and co-workers reported the
synthesis of β-alkoxy sulfones through an electrochemical
oxidative alkoxysulfonylation of alkenes starting from sulfonyl
hydrazines and alcohols.7 In their approaches, the preinstalled
sulfonyl compounds or odorous thiol substrates had to be
utilized.8 As part of our continuous interest in the sulfonylation
reaction with the insertion of sulfur dioxide, we considered that
the preparation of β-substituted sulfones from the sulfur
dioxide surrogate of inorganic sulfite would be ideal.
In the past few years, reactions of iminyl radicals have
attracted much attention.9,10 For instance, Yu and co-workers
described the intermolecular remote C(sp3)−H and C−C
vinylation of O-acyl oximes with vinyl boronic acids via iminyl
Received: April 15, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.9b01323
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(Table 1, entry 4). The yield was higher when the light source
(35 W white LED) was changed to 15 W blue LED (Table 1,
entry 5). The result could be improved when the reaction was
performed in a mixed solvent of MeOH/MeCN, leading to the
corresponding product 3a in 80% yield (Table 1, entry 6). The
yields were inferior when other solvents were used (Table 1,
entries 7−9). The yield was reduced to 29% with 10 equiv of
methanol. No further improvement could be obtained when
the amount of reactants was changed (data not shown in Table
1).
Scheme 1. Proposed Multicomponent Reaction of O-Acyl
Oximes, Sulfur Dioxide, Alkenes, and Nucleophiles under
Visible-Light Irradiation
With the above optimized conditions in hand, we started to
explore the substrate scope for the multicomponent reaction of
O-acyl oxime 1a, potassium metabisulfite, alkenes 2, and
methanol under visible light irradiation. The result is
summarized in Scheme 2. A wide range of alkenes could be
Scheme 2. Scope Exploration for the Reaction of O-Acyl
Oxime 1a, Potassium Metabisulfite, Alkenes 2, and
a
Methanol
Initial studies were carried out with the reaction of
cyclobutanone O-(4-(trifluoromethyl)benzoyl) oxime 1a,
potassium metabisulfite, 4-(prop-1-en-2-yl)-1,1′-biphenyl 2a,
and methanol under visible-light irradiation (Table 1). At the
Table 1. Initial Studies for the Reaction of Cyclobutanone
O-(4-(Trifluoromethyl)benzoyl) Oxime 1a, Potassium
Metabisulfite, 4-(Prop-1-en-2-yl)-1,1′-biphenyl 2a, and
a
Methanol under Visible-Light Irradiation
b
yield
entry
1
PC
solvent
light
(%)
Ru(bpy)3Cl2·
6H2O
MeOH
35 W white
nr
2
3
4
5
6
7
8
9
Eosin Y
Fluorescein
Ir(ppy)3
Ir(ppy)3
Ir(ppy)3
Ir(ppy)3
Ir(ppy)3
Ir(ppy)3
MeOH
MeOH
MeOH
MeOH
MeOH/MeCN (3:1)
MeOH/DCE (3:1)
MeOH/PhMe (3:1)
35 W white
35 W white
35 W white
15 W blue
15 W blue
15 W blue
15 W blue
15 W blue
nr
trace
42
50
80
66
66
65
a
Reaction conditions: cyclobutanone O-(4-(trifluoromethyl)benzoyl)
oxime 1a (0.2 mmol), K2S2O5 (0.22 mmol), alkene 2 (0.3 mmol),
MeOH/MeCN (v/v = 3:1, 2 mL), N2. Isolated yield based on
cyclobutanone O-(4-(trifluoromethyl)benzoyl) oxime 1a.
b
employed in the reaction under the standard conditions. This
transformation was highly effective, and diverse β-methoxy
sulfones were generated in moderate to good yields. Addi-
tionally, different functionalities were tolerated. For instance,
the ester-containing product 3g was produced in 54% yield.
The benzofuranyl-substituted compound 3m was obtained in
44% yield. The structure of compound 3i was confirmed by the
X-ray diffraction analysis (see the Supporting Information),
which showed the excellent chemoselectivity during the
reaction process.
MeOH/1,4-dioxane
(3:1)
MeCN
c
10
Ir(ppy)3
15 W blue
29
a
Reaction conditions: cyclobutanone O-(4-(trifluoromethyl)benzoyl)
oxime 1a (0.2 mmol), K2S2O5 (0.22 mmol), 4-(prop-1-en-2-yl)-1,1′-
b
biphenyl 2a (0.3 mmol), solvent (2.0 mL), N2, 20 h. Isolated yield
based on cyclobutanone O-(4-(trifluoromethyl)benzoyl) oxime 1a.
In the presence of MeOH (10 equiv).
c
outset, the reaction was screened with several photocatalysts.
No reaction occurred in the presence of Ru(bpy)3Cl2·6H2O or
eosin Y under visible-light irradiation (Table 1, entries 1 and
2). Only a trace amount of product was observed when
fluorescein was used as a replacement (Table 1, entry 3).
Gratifyingly, the reaction provided the desired product 3a in
42% yield when Ir(ppy)3 was utilized as the photocatalyst
Subsequently, a range of O-acyl oximes 1 was examined in
the reaction of potassium metabisulfite, 4-(prop-1-en-2-yl)-
1,1′-biphenyl 2a, and methanol under the standard conditions
(Scheme 3). As expected, all reactions worked well to provide
the corresponding products in good yields. The bromo-, ester-,
and nitrogen-containing heterocycle were all compatible
during the transformation.
B
DOI: 10.1021/acs.orglett.9b01323
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Organic Letters
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Scheme 3. Reaction of O-Acyl Oximes 1, Potassium
Metabisulfite, Alkene 2a, and Methanol
Scheme 5. Reaction of O-Acyl Oximes 1, Potassium
Metabisulfite, Alkenes 2, and H2O
a
a
a
Reaction conditions: O-acyl oxime 1 (0.2 mmol), K2S2O5 (0.22
mmol), alkene 2 (0.3 mmol), H2O/MeCN (v/v = 1:2, 3.0 mL), N2.
Isolated yield based on cyclobutanone O-acyl oxime 1.
b
the corresponding product in 68% yield (Scheme 6, eq a). It
was also found that the oxygen-containing substrate 6 was
Scheme 6. Further Exploration
a
Reaction conditions: O-acyl oxime 1 (0.2 mmol), K2S2O5 (0.22
mmol), alkene 2a (0.3 mmol), MeOH/MeCN (v/v = 3:1, 2.0 mL),
b
N2. Isolated yield based on cyclobutanone O-acyl oxime 1.
This method was further extended to other alcohols
(Scheme 4). When methanol was replaced by ethanol or
Scheme 4. Reaction of O-Acyl Oximes 1a, Potassium
a
Metabisulfite, Alkene 2a, and Other Alcohols
suitable under the conditions, which gave rise to the desired
product 7 in 50% yield (Scheme 6, eq b). However, no
reaction occurred when O-acyl oxime 8 was employed in the
reaction (Scheme 6, eq c). To gain more insight of the
mechanism, 2.0 equiv of 2,2,6,6-tetramethyl-1-piperidinyloxy
(TEMPO) was added in the reaction of O-acyl oxime 1b,
potassium metabisulfite, and 4-(prop-1-en-2-yl)-1,1′-biphenyl
2a under the standard conditions (Scheme 6, eq d). The result
showed that no desired product 3p was detected. Instead,
compound 9 was obtained in 33% yield. This outcome
demonstrated that a radical process might be involved.
Additionally, the quantum yield for the reaction of O-acyl
oxime 1a, K2S2O5, and alkene 2a under the standard condition
was determined as 20%, which demonstrated it was a
photoredox-catalyzed pathway (see the Supporting Informa-
tion). These results were consistent with the hypothesis shown
in Scheme 1. Furthermore, the p-CF3-benzoyl part in oxime
would undergo cleavage via a SET process in the presence of
Ir(ppy)3, which would combine with H+ from nucleophile later
affording the corresponding benzoic acid. The formation of
a
Reaction conditions: O-acyl oxime 1a (0.2 mmol), K2S2O5 (0.22
mmol), alkene 2a (0.3 mmol), R1OH/MeCN (v/v = 3:1, 2.0 mL),
N2. Isolated yield based on cyclobutanone O-acyl oxime 1a.
b
ethane-1,2-diol in the reaction of oxime 1a, the corresponding
compounds 4a and 4d were afforded in moderate yields. We
also examined the reactions of secondary alcohol and tertiary
alcohol. For example, compound 4b was obtained in 37% yield
when propan-2-ol was used as the nucleophilic component.
However, only a trace amount of product was detected with 2-
methylpropan-2-ol as the solvent. The results showed that
secondary and tertiary alcohols were not good solvents in this
transformation. The reaction in methan-d3-ol-d instead of
methanol gave rise to the desired product 4c in 65% yield.
Additionally, β-hydroxy sulfones 5 were generated in 32−47%
yields when the reactions were performed in a mixture of water
and MeCN (Scheme 5).
Further exploration showed that a gram-scale reaction for
the synthesis of compound 3a worked effectively to generate
C
DOI: 10.1021/acs.orglett.9b01323
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Organic Letters
Letter
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benzoic acid could be observed in the reaction system and
confirmed by 19F NMR.
In conclusion, we have described a photoredox-catalyzed
multicomponent sulfonylation of O-acyl oximes via iminyl
radicals with the insertion of sulfur dioxide. The commercially
available potassium metabisulfite as the source of sulfur dioxide
works efficiently in this transformation. Not only alcohols but
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alkoxy sulfones and β-hydroxyl sulfones with good functional
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ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.9b01323.
1
Experimental procedures, characterization data, H and
13C NMR spectra of products (PDF)
Accession Codes
(5) (a) Oida, S.; Tajima, Y.; Konosu, T.; Nakamura, Y.; Somada, A.;
Tanaka, T.; Habuki, S.; Harasaki, T.; Kamai, Y.; Fukuoka, T.; Ohya,
S.; Yasuda, H. Chem. Pharm. Bull. 2000, 48, 694. (b) Xie, W.; Wu, Y.;
Zhang, J.; Mei, Q.; Zhang, Y.; Zhu, N.; Liu, R.; Zhang, H. Eur. J. Med.
Chem. 2018, 145, 35. (c) Xie, W.; Xie, S.; Zhou, Y.; Tang, X.; Liu, J.;
Yang, W.; Qiu, M. Eur. J. Med. Chem. 2014, 81, 22. (d) Xie, W.;
Zhang, H.; He, J.; Zhang, J.; Yu, Q.; Luo, C.; Li, S. Bioorg. Med. Chem.
Lett. 2017, 27, 530.
CCDC 1898774 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
́
(6) (a) Fu, X.; Meng, Y.; Li, X.; Stepien, M.; Chmielewski, P. J.
■
́
Chem. Commun. 2018, 54, 2510. (b) Li, X.; Meng, Y.; Yi, P.; Stepien,
M.; Chmielewski, P. J. Angew. Chem., Int. Ed. 2017, 56, 10810.
*E-mail: jie_wu@fudan.edu.cn.
*E-mail: ysq0607@gmail.com.
ORCID
́
(c) Liu, B.; Yoshida, T.; Li, X.; Stepien, M.; Shinokubo, M.;
Chmielewski, P. J. Angew. Chem., Int. Ed. 2016, 55, 13142. (d) Deng,
́
Z.; Li, X.; Stepien, M.; Chmielewski, P. J. Chem. - Eur. J. 2016, 22,
4231. (e) Deng, K.; Li, X.; Huang, H. Electrochim. Acta 2016, 204, 84.
Jie Wu: 0000-0002-0967-6360
Notes
́
(f) Liu, B.; Li, X.; Stepien, M.; Chmielewski, P. J. Chem. - Eur. J. 2015,
21, 7790. (g) Liu, B.; Fang, H.; Li, X.; Cai, W.; Bao, L.; Rudolf, M.;
Plass, F.; Fan, L.; Lu, X.; Guldi, D. M. Chem. - Eur. J. 2015, 21, 746.
The authors declare no competing financial interest.
́
(h) Liu, B.; Li, X.; Maciołek, J.; Stepien, M.; Chmielewski, P. J. J. Org.
́
Chem. 2014, 79, 3129. (i) Liu, B.; Li, X.; Xu, X.; Stepien, M.;
ACKNOWLEDGMENTS
■
Chmielewski, P. J. J. Org. Chem. 2013, 78, 1354. (j) Li, X.; Liu, B.;
Chmielewski, P. J.; Xu, X. J. Org. Chem. 2012, 77, 8206. (k) Li, X.;
Liu, B.; Yu, X.; Yi, P.; Yi, R.; Chmielewski, P. J. J. Org. Chem. 2012, 77,
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Financial support from National Natural Science Foundation
of China (Nos. 21672037 and 21532001) is gratefully
acknowledged.
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2178.
E
DOI: 10.1021/acs.orglett.9b01323
Org. Lett. XXXX, XXX, XXX−XXX