Copper-Catalyzed Annulation or Homocoupling of Sulfoxonium Ylides: Synthesis of 2,3-Diaroylquinolines or α,α,β-Tricarbonyl Sulfoxonium Ylides

Article abstract of DOI:10.1021/acs.orglett.0c00085

An unprecedented copper-catalyzed reaction of sulfoxonium ylides and anthranils is reported that enables an easy access to 2,3-diaroylquinolines through a [4+1+1] annulation. Copper-catalyzed homocoupling of sulfoxonium ylides provided α,α,β-tricarbonyl sulfoxonium ylides, which provides a strategy to extend the carbon chain through C-C bond formation. The utility of the products as well as the mechanistic details of the process are presented.

Full text of DOI:10.1021/acs.orglett.0c00085

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Letter
Copper-Catalyzed Annulation or Homocoupling of Sulfoxonium
Ylides: Synthesis of 2,3-Diaroylquinolines or α,α,β-Tricarbonyl
Sulfoxonium Ylides
Shuai Zhu,§ Kai Shi,§ Hao Zhu, Zhe-Kang Jia, Xiao-Feng Xia, Dawei Wang, and Liang-Hua Zou*
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ABSTRACT: An unprecedented copper-catalyzed reaction of sulfoxo-
nium ylides and anthranils is reported that enables an easy access to
2,3-diaroylquinolines through a [4+1+1] annulation. Copper-catalyzed
homocoupling of sulfoxonium ylides provided α,α,β-tricarbonyl
sulfoxonium ylides, which provides a strategy to extend the carbon
chain through C−C bond formation. The utility of the products as well
as the mechanistic details of the process are presented.
Very recently, more economical annulation reactions of
sulfoxonium ylides have been developed by Ackermann,6
Wang7 and Zeng8 using a low-cost RuII catalyst (Scheme 1a,
left). In contrast to these attempts within this category that
focused on [n+2] annulation, a few examples of Rh-catalyzed
[n+1] annulation have also been investigated (Scheme 1a,
right).9 Consequently, the development of general protocols
for the synthesis of sulfoxonium ylides has attracted
considerable attention.10 Recently, several methods have
been reported for the synthesis of α,α-dicarbonyl sulfoxonium
ylides (Scheme 1b).11 To the best of our knowledge, however,
there have been no documented examples of the formation of
tricarbonyl sulfoxonium ylides.
ulfoxonium ylides have become popular carbene surrogates
Sdue to their operational safety and synthetic convenience,
and they have been widely employed to numerous types of
organic transformations in the field of natural products,
pharmaceuticals and chemical materials.1 In addition,
sulfoxonium ylides are widely used as versatile carbenoid
precursors in X−H (X = C, N, O, S) insertion reactions. Many
pioneering work relying noble metal catalysts, such as Rh or Ir,
to create various heterocyclic or carbocyclic molecules were
reported by Vaitla,2 Li,3 Cheng4 and others5 (Scheme 1a, left).
Scheme 1. Representative Annulation and Synthesis of
Sulfoxonium Ylides
In the past years, significant progress has been made in
transition-metal-catalyzed reactions for carbon−carbon and
carbon-heteroatom bond formation.12 In particular, copper
catalysis has now emerged as one of the most ideal catalytic
approaches for the synthesis of a variety of value-added bulk
and fine chemicals due to the relatively low price and rich
reserves.13 In this regard, our group has recently developed a
copper-catalyzed oxidative method for the preparation of
quinolines starting from anthranils and oxo-compounds.14
Quinolines and their derivatives represent a class of significant
heterocyclic compounds that are widely found in natural
products,15 drugs,16 useful ligands,17 and functional materi-
als.18 Functionalized quinolines exhibit broad bioactivities,
such as antimalaria, anti-inflammatory, antiasthma, antibacte-
rial, and antiallergic effects.19 Therefore, we were stimulated to
Received: January 8, 2020
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© XXXX American Chemical Society
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explore a novel strategy for the synthesis of quinolines using
sulfoxonium ylides instead of oxo-compounds.20
yield) under the optimized conditions (Table 1, entry 13),
which could account for the somewhat low yield of this
reaction.
With the optimized reaction conditions in hand (Table 1,
entry 13), the scope of the reaction of sulfoxonium ylide 1a
with a variety of anthranils 2 was investigated and the results
are summarized in Scheme 2. For the substrates containing −F,
As part of our ongoing interest in the synthesis of
heterocycles,14,21 we report our findings on copper-catalyzed
synthesis of 2,3-diaroylquinolines through [4+1+1] annulation
of sulfoxonium ylides and anthranils (Scheme 1c, right).22
Moreover, an efficient protocol for the synthesis of α,α,β-
tricarbonyl sulfoxonium ylides is also presented (Scheme 1c,
left).
a
Scheme 2. Substrate Scope of the [4+1+1] Annulation
The initial optimization of the reaction conditions was
conducted with sulfoxonium ylide 1a and anthranil 2a as
substrates, and all of the results are summarized in Table 1 (for
Table 1. Optimization of Reaction Conditions for the
a
Synthesis of 3a
entry
catalyst
additive
ligand
solvent
yield (3a) (%)
1
2
3
4
5
6
7
8
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
CuCl
Cu2O
Cu(OTf)2
CuI
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
PPh3
PPh3
PPh3
PPh3
PPh3
THF
25
36
28
trace
trace
40
35
20
20
21
25
46
68
0
DMF
DMSO
MeCN
DCM
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
9
a
10
11
12
13
14
15
16
Reaction conditions: 1 (0.3 mmol), 2 (0.2 mmol), copper powder
(10 mol %), AgOTf (10 mol %), DMF (2 mL), 90 °C, under an
atmosphere of dioxygen, 12 h.
CuBr
Cu0
b
Cu0
−Cl and −Br groups at the para-position of the nitrogen atom
in the benzene ring, the reaction provided the corresponding
products 3b−3d in 51%, 52% and 50% yields, respectively.
Considering the possible influence of steric effects, reactions of
other substrates with halogen groups −F, −Cl and −Br
produced products 3e−3g in 45%, 51% and 62% yields,
respectively. One substrate bearing the strong electron-
withdrawing substituent −CF3 was also successfully employed
in the reaction, yielding product 3h in 41% yield.
To further explore the scope of the reaction, a series of
sulfoxonium ylides 1 bearing various substituents were
investigated and the results are summarized in Scheme 2.
The reaction of the substrate containing a methyl group with
anthranil 2a provided product 3i in 40% yield. Next substrates
bearing halogen groups −F, −Cl and −Br were successfully
employed in the reaction, creating products 3j−3l in yields
varying from 35% to 42%. For the substrates with strong
electron-withdrawing substituents −OCF3 and −CF3, the
reaction also proceeded well, affording the corresponding
products 3m and 3n in 25% and 40% yields, respectively.
Considering the steric factor, the reaction was turned to
substrates bearing substituents −Me, −F and −Cl at the meta-
position of the benzene ring and products 3o−3q were
obtained in 36%, 30% and 28% yields, respectively.
Subsequently, substrates with substituents −Me, −F and −Cl
at the ortho-position of the benzene ring were also tested and
products 3r−3t were produced in 40%, 45% and 42% yields,
respectively. In addition, the substrates containing two −Me or
Cu0
Cu0
trace
c
AgOTf
20
a
Reaction conditions: 1a (0.3 mmol), 2a (0.2 mmol), catalyst (10
mol %), additive (10 mol %), ligand (10 mol %), solvent (2 mL), 110
°C, under an atmosphere of dioxygen, 12 h. 90 °C. Under an
atmosphere of argon. Yield based on 1a.
b
c
details see Supporting Information). Using 1a and 2a at a 1.5:1
ratio, Cu(OAc)2 (10 mol %) as catalyst, AgOTf (10 mol %) as
an additive, PPh3 (10 mol %) as a ligand, and THF as a
solvent, the desired product 3a was isolated in 25% yield after
stirring at 110 °C for 12 h (Table 1, entry 1). The screening of
solvents showed that DMF was the best solvent (Table 1,
entries 2−5). Moreover, the yield was increased to 40% when
the ligand was omitted from the reaction (Table 1, entry 6).
Other copper salts and copper powder were tested in the
reaction and the results showed that copper powder was most
effective for this transformation, affording product 3a in 46%
yield (Table 1, entries 7−12). The reaction was tested at
different reaction temperatures and a better yield of 68% was
achieved at 90 °C (Table 1, entry 13). Almost no product 3a
was obtained in the absence of copper powder or AgOTf
(Table 1, entries 14 and 15). Notably, product 3a was obtained
in 20% yield when the reaction was performed under an
atmosphere of argon, indicating that dioxygen played an
important role in the reaction (Table 1, entry 16).23 It should
be noted that homocoupling product 4a was also formed (25%
B
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a
−F substituents at the meta-position were also successfully
employed in the reaction, affording products 3u and 3v in 51%
and 32% yields, respectively. The substrate bearing a naphthyl
group also reacted well with anthranil 2a under the optimized
reaction conditions, providing the desired product 3w in 42%
yield. Furthermore, one substrate containing a heterocycle
(thienyl) also reacted well with 2a, giving product 3x in 61%
yield. Unfortunately, some substrates bearing electron-
donating substituents, such as −OMe and −NMe2, were not
suitable for this transformation.
Scheme 4. Substrate Scope of Sulfoxonium Ylides
α,α,β-Tricarbonyl sulfoxonium ylide 4a was isolated in 23%
yield when the reaction was performed in the absence of 2a
(Scheme 3a). It should be noted that compound 4a was
Scheme 3. Homocoupling of 1a for the Synthesis of 4a
a
Reaction conditions: 1 (0.2 mmol), Cu(OAc)2 (10 mol %),
CF3COOAg (10 mol %), dioxane (2 mL), 90 °C, under an
atmosphere of dioxygen, 12 h.
excluded from serving as an intermediate for the three-
component reaction described above since the reaction did not
proceed when compound 4a was employed instead of 1a in the
reaction, and the reaction was characterized by 95% recovery
of the starting material 4a (Scheme 3b). Due to the remarkable
importance and novelty of α,α,β-tricarbonyl sulfoxonium
ylides, we were stimulated to investigate the homocoupling
reaction of compound 1a (for details on the screening of
reaction conditions, see Supporting Information).
affording products 4v and 4w in 55% and 64% yields,
respectively. Finally, substrates bearing alkyl groups were also
investigated in the reaction. The reaction of a substrate
containing cyclohexyl resulted in product 4x in an acceptable
yield of 51%. Furthermore, one substrate with a long carbon
chain afforded product 4y in 18% yield.
To demonstrate the synthetic utility of this protocol, several
transformations of products 3a and 4a were performed
(Scheme 5). 1,4-Diphenylpyridazino[4,5-b]quinolone (5) was
With the optimized reaction conditions in hand (see
Supporting Information), the scope of the homocoupling
reaction of sulfoxonium ylides 1 was investigated and the
results are summarized in Scheme 4. For the substrates
containing the electron-donating substituents −Me and −OMe
at the para-position, the reaction provided the corresponding
products 4b and 4c in 81% and 72% yields, respectively.
Substrates bearing halogen groups −F, −Cl and −Br as well as
the electron-withdrawing substituent −OCF3 afforded the
corresponding products 4d−4g in good yields varying from
68% to 80%. It should be noted that strong electron-
withdrawing substituents could also be tolerated in the
reaction, yielding products 4h−4j in good yields (67%, 56%
and 61%, respectively). For the substrates bearing −Me, −F
and −Cl at the ortho-position, products 4k−4m were obtained
in 61%, 60% and 61% yields, respectively. For the substrates
bearing −Me, −F and −Cl at the meta-position, the reaction
proceeded very well, affording products 4n−4p in 82%, 65%
and 73% yields, respectively. Furthermore, the substrates
containing two −Me, −F, −Cl, or −CF3 substituents at the
meta-position were also successfully employed in the reaction,
giving products 4q−4t in yields varying from 42% to 82%. It
seems that electron-donating substituents exhibited much
better efficiency that electron-withdrawing ones. The substrate
bearing a naphthyl group also reacted well under the optimized
reaction conditions, forming the desired product 4u in 42%
yield. Moreover, heterocycle substrates containing furyl or
thienyl groups could also be employed in the reaction,
Scheme 5. Synthetic Transformation of Products
obtained in 83% yield via the reaction of compound 3a with
hydrazine hydrate in hot methanol. In addition, the reduction
of compound 3a resulted in product 6 in 59% yield in the
presence of NaBH4. Finally, the reaction of compound 3a with
methylamine produced 1,3-diphenyl-2-methylpyrrolo[3,4-b]-
quinolone (7) in 75% yield, which could be further
C
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transformed to complex product 8 in 79% yield through the
Diels−Alder reaction. It is noteworthy that product 7 was
unstable under air, and so it was very difficult to obtain clean
1H NMR spectra. Similarly, the transformation of compound
4a gave products 9 and 10 through the reaction of 4a with
methylamine or hydrazine in 44% and 29% yields, respectively.
To elucidate the possible mechanism of the reaction, several
preliminary experiments were carried out (Scheme 6). At first,
Scheme 7. Proposed Mechanism for the Synthesis of 3a and
4a
Scheme 6. Control Reactions
with the release of DMSO, which coordinates 2a to afford
intermediate IV. Then intermediate V is formed, which
transforms to intermediate VI. Finally, product 3a is formed
through a dehydration process. With regard to the synthesis of
4a, a possible mechanism is also proposed as route b in
Scheme 7. A peroxy intermediate VII is formed in the presence
of molecular oxygen,25 which results in the final product 4a
through dehydration.
In conclusion, a significant transformation of sulfoxonium
ylides has been developed for the direct construction of 2,3-
diaroylquinolines through the [4+1+1] annulation of sulfoxo-
nium ylides with anthranils in the presence of a copper catalyst.
Furthermore, a protocol has been unexpectedly found for the
preparation of a novel class of sulfoxonium ylides. A broad
range of substituents were well tolerated for both reaction
protocols, and a series of 2,3-diaroylquinolines and α,α,β-
tricarbonyl sulfoxonium ylides were synthesized in acceptable
to high yields. Moreover, applications of the related products,
as well as the mechanistic details, were investigated.
2-aminobenzaldehyde (11) was employed instead of anthranil
2a to investigate whether it was an intermediate in the process,
affording product 3a in 20% yield (Scheme 6, eq a). The
results showed that 2-aminobenzaldehyde might be the
intermediate for the transformation of anthranil 2a. Fur-
thermore, radical scavengers, such as 2,6-bis(1,1-dimethyleth-
yl)-4-methylphenol (BHT) and 2,2,6,6-tetramethyl-1-piperidi-
nyloxy (TEMPO), were tested in the reaction, and they
dramatically suppressed the reaction (Scheme 6, eq b). In
addition, a set of intermolecular competition reactions between
different p-substituted sulfoxonium ylides (1b and 1g) with 2a
were investigated (Scheme 6, eq c). In this case, product 3i was
obtained in 25% yield, but product 3n was not formed.
Interestingly, a mixture of products 12 and 13 (the ratio of
products 12 and 13 was 1:1) was produced in 30% yield. The
superior behavior of 1b revealed that electron-rich sulfoxonium
ylide had higher reactivity. Next, anthranil 2a and electron-
withdrawing compound 2d containing a −Br group were also
tested in the competition reaction, providing products 3a and
3d in 21% and 18% yields, respectively (Scheme 6, eq d).
These results showed that there were no significant differences
in reactivity of anthranils with electron-rich or electron-
withdrawing substituents. To test the scalability of the new
protocol, we performed the reaction on a gram scale under the
optimized conditions (synthesis of 4a) to afford product 4a
with a good yield of 78% (639.8 mg).
ASSOCIATED CONTENT
* Supporting Information
■
sı
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.0c00085.
Experimental procedures, characterization data, and
NMR spectra (PDF)
Accession Codes
CCDC 1949069 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.
On the basis of our results and previous reports on
sulfoxonium ylides,1a,b a possible mechanism on the synthesis
of 3a is proposed as shown in route a in Scheme 7. First,
copper powder is oxidized in situ to generate an active cationic
CuII species in the presence of Ag salts.24 The reaction of
sulfoxonium ylide 2a forms carbene copper I with the release
of DMSO. Intermediate II is formed via the insertion of
carbene I into 1a. A second carbene copper III is generated
AUTHOR INFORMATION
Corresponding Author
■
Liang-Hua Zou − Key Laboratory of Carbohydrate Chemistry
and Biotechnology, Ministry of Education, School of
Pharmaceutical Sciences, Jiangnan University, Wuxi 214122,
D
https://dx.doi.org/10.1021/acs.orglett.0c00085
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Letter
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Jiangsu Province, P.R. China; orcid.org/0000-0003-0939-
6016; Email: zoulianghua@jiangnan.edu.cn
Authors
Shuai Zhu − Key Laboratory of Carbohydrate Chemistry and
Biotechnology, Ministry of Education, School of Pharmaceutical
Sciences, Jiangnan University, Wuxi 214122, Jiangsu Province,
P.R. China
Kai Shi − Key Laboratory of Carbohydrate Chemistry and
Biotechnology, Ministry of Education, School of Pharmaceutical
Sciences, Jiangnan University, Wuxi 214122, Jiangsu Province,
P.R. China
Hao Zhu − Key Laboratory of Carbohydrate Chemistry and
Biotechnology, Ministry of Education, School of Pharmaceutical
Sciences, Jiangnan University, Wuxi 214122, Jiangsu Province,
P.R. China
Zhe-Kang Jia − Key Laboratory of Carbohydrate Chemistry and
Biotechnology, Ministry of Education, School of Pharmaceutical
Sciences, Jiangnan University, Wuxi 214122, Jiangsu Province,
P.R. China
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Xiao-Feng Xia − School of Chemical and Material Engineering,
Jiangnan University, Wuxi 214122, Jiangsu Province, P.R.
China; orcid.org/0000-0002-1837-0638
Dawei Wang − School of Chemical and Material Engineering,
Jiangnan University, Wuxi 214122, Jiangsu Province, P.R.
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Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.0c00085
Author Contributions
§S.Z. and K.S. contributed equally to this work.
Notes
The authors declare no competing financial interest.
(13) (a) Allen, S. E.; Walvoord, R. R.; Padilla-Salinas, R.; Kozlowski,
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ACKNOWLEDGMENTS
■
This work was financially supported by NSF of Jiangsu
Province (BK20150129) and the Top-notch Academic
Programs Project of Jiangsu Higher Education Institutions
(No. PPZY2015B146). L.Z. acknowledges Professor Carsten
Bolm (RWTH Aachen University) for his valuable discussions
and help with this work.
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