Palladium-Catalyzed Oxidative [2 + 2 + 1] Annulation of 1,7-Diynes with H2O: Entry to Furo[3,4- c]quinolin-4(5 H)-ones

Article abstract of DOI:10.1021/acs.orglett.8b02883

A novel cascade annulation of 1,7-diynes with water has been developed for the synthesis of furo[3,4-c]quinolin-4(5H)-one skeletons with high atom- and step-economy. The transformation was enabled by a palladium catalyst in the presence of copper salt as

Full text of DOI:10.1021/acs.orglett.8b02883

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Palladium-Catalyzed Oxidative [2 + 2 + 1] Annulation of 1,7-Diynes
with H2O: Entry to Furo[3,4‑c]quinolin-4(5H)‑ones
Xuan-Hui Ouyang,†,§ Fang-Lin Tan,†,§ Ren-Jie Song,*,† Wei Deng,† and Jin-Heng Li*,†,‡
†Key Laboratory of Jiangxi Province for Persistent Pollutants Control and Resources Recycle, Nanchang Hangkong University,
Nanchang 330063, China
‡State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, China
S
* Supporting Information
ABSTRACT: A novel cascade annulation of 1,7-diynes with
water has been developed for the synthesis of furo[3,4-
c]quinolin-4(5H)-one skeletons with high atom- and step-
economy. The transformation was enabled by a palladium
catalyst in the presence of copper salt as the promoter,
involving the formation of one C−C bond and two C−O
bonds. Moreover, the reaction exhibits good tolerance of functional groups and broad substrate scope. Notably, the control
experiments support the incorporation of the new oxygen atom from water.
uro[3,4-c]quinolin-4(5H)-ones are common motifs of
many natural products and bioactive molecules that have
gained increased attention from the synthetic chemistry and
pharmaceutical industries in recent years.1 Such compounds
have shown activity against bacteria,1a−e lymphoma,1f,g
hepatocellular disease,1h and n-NOS1i (Figure 1). Current
Scheme 1. Annulation toward Furo[3,4-c]quinolin-4(5H)-
ones
F
be efficient for this transformation. For instance, the Hirao and
Chan group reported the gold-catalyzed cycloisomerization of
1,6-diyne to furnish 2,4a-dihydro-1H-fluorenes.11a Hao, Tu,
Jiang, and co-workers next established a metal-free domino
cyclization of 1,7-diynes for the construction of fused aza-
heterocyclic synthesis in two steps under microwave
conditions.11b Recently, we and other groups constructed a
functionalized polycyclic ring through cascade annulation of
enynes.12 With continued interest in the synthesis of polycyclic
rings, herein we report a method that directly converted 1,7-
diynes to furo[3,4-c]quinolin-4(5H)-ones under a Pd/Cu
catalyst system (Scheme 1b). Notably, it was confirmed that
the newly formed oxygen atom came from water.
Figure 1. Important examples of bioactive furo[3,4-c]quinolin-4(5H)-
one derivatives.
methods for the synthesis of these compounds mainly focus on
the cycloaddition reaction of aniline derivatives with α,β-
unsaturated carbonyl compounds,2 as well as an imino-Diels−
Alder reaction of N-arylimine with olefins (Scheme 1a).3
However, most of these methods suffer from the requirement
of a stoichiometric amount of expensive Lewis acids with
limited substrate scope. As a result, the development of step-
economical and cost-effective methods for the synthesis of
furo[3,4-c]quinolin-4(5H)-one derivatives is highly appealing.
Transition-metal-catalyzed inter- and intramolecular tandem
annualtion of diynes has been recognized as a versatile
synthetic approach for substituted polycyclic molecules with
excellent atom-economy.4−10 To date, Rh,4 Ru,5 Au,6 Pt,7 Ni,8
Pd,9 and other transition metal catalysts10 have been proven to
We began our studies by using N-methyl-3-phenyl-N-(2-
(phenylethynyl)phenyl)propiolamide 1a as a model substrate,
and a summary of results are provided in Table 1. Gratifyingly,
Received: September 10, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b02883
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
With the optimized conditions in hand, we investigated the
substrate scope of this tandem cyclization reaction with respect
to N-(o-ethynlaryl)propiolamides 1 (Scheme 2). A wide range
Table 1. Screening of Optimal Reaction Conditions
Scheme 2. Variation of the N-(o-Ethynlaryl)propiolamides
a
(1)
entry
variation from the standard conditions
yield (%)
1
2
none
without PdCl2
84
0
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Pd(OAc)2 instead of PdCl2
PdBr2 instead of PdCl2
Pd(PPh3)4Cl2 instead of PdCl2
Pd(PPh3)4 instead of PdCl2
PdCl2 (10 mol %)
PdCl2 (2 mol %)
without CuBr2
Cu(OAc)2 instead of CuBr2
Cu(OTf)2 instead of CuBr2
CuBr instead of CuBr2
CuBr2 (20 mol %)
CuBr2 (5 mol %)
DMSO instead of DMF
MeCN instead of DMF
toluene instead of DMF
at 120 °C
59
72
10
5
83
72
23
61
62
58
83
48
61
38
15
67
42
78
11
72
63
77
at 80 °C
air instead of O2
argon instead of O2
H2O (6 equiv)
H2O (2 equiv)
b
24
none
a
Reaction conditions: 1a (0.2 mmol), PdCl2 (5 mol %), CuBr2 (10
mol %), H2O (4 equiv), DMF (2 mL), O2 (1 atm), 100 °C and 24 h.
b
1a (1 mmol) for 36 h.
84% yield of desired product 5-methyl-1,3-diphenylfuro[3,4-
c]quinolin-4(5H)-one 2a was obtained when 5 mol % of PdCl2
was used as the catalyst in combination with 10 mol % of
CuBr2 in the presence of H2O and DMF at 100 °C (entry 1).
However, no desired product 2a was observed in the absence
of PdCl2 catalyst (entry 2). Other palladium salts, such as
Pd(OAc)2, PdBr2, Pd(PPh3)4Cl2, and Pd(PPh3)4, were also
reactive, but they were all less reactive than PdCl2 (entry 1 vs
entries 3−6). Identical yield of 2a was generated when the
loading of PdCl2 was increased to 10 mol %, whereas 72% yield
of 2a was obtained when 2 mol % of PdCl2 was used (entries 7
and 8). Copper salts played an important role in this reaction,
as only 23% of 2a was observed when the reaction was
performed without CuBr2 (entry 9). Next, different copper
salts and the amount of copper salts were investigated, and the
best result was obtained when 10 mol % of CuBr2 was used as
an additive (entry 1 vs entries 10−14). Subsequently, a series
of solvents, such as DMSO, MeCN, and toluene, were
evaluated, and they showed reactivity lower than that of
DMF (entry 1 vs entries 15−17). Further screening of other
parameters such as temperature and atmosphere environment
did not improve the reaction yield (entries 18−21). Finally, the
amount of H2O affected the yield, and 4 equiv of H2O was
suggested to be the best choice (entry 1 vs entries 22 and 23).
We found that the reaction on a 1 mmol scale of substrate 1a
was successfully performed in 77% yield (entry 24).
a
Reaction conditions: 1 (0.2 mmol), PdCl2 (5 mol %), CuBr2 (10
mol %), H2O (4 equiv), DMF (2 mL), O2 (1 atm), 100 °C and 24 h.
of substrates were successfully transformed under the standard
reaction conditions and provided the corresponding furo[3,4-
c]quinolin-4(5H)-ones in moderate to good yields. The N-Bn-
substituted 1,7-diyne 1b could convert to the desired product
2b in 64% yield under a PdCl2/CuBr2 system. Unfortunately,
substrate 1c with a free N-H bond was not a viable substrate
under these conditions. Alternatively, phenol-linked 1,7-diyne
1d was proven to be a suitable reaction partner toward
synthesizing 1,3-diphenyl-4H-furo[3,4-c]chromen-4-one 2d
with 68% yield. A variety of N-(o-ethynlaryl)propiolamides
with different functional groups, such as Me, OMe, Br, and CN
groups, at different positions of the arylalkynyl (R2) moiety,
could be successfully converted to the corresponding products
2e−j with 59−91% yields. For instance, 1,7-diynes having
either electron-donating (OMe, 1f) or electron-withdrawing
(CN, 1h) substituents readily participated in this tandem
cyclization, and gave the furo[3,4-c]quinolin-4(5H)-ones 2f
and 2h in 91% and 59% yields, respectively. Moreover, 1,7-
B
DOI: 10.1021/acs.orglett.8b02883
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
diyne 1k possessing a heteroaryl group, such as 2-thienyl,
worked well (product 2k). Other 1,7-diynes 1l and 1m by
installing a n-butyl or cyclopropyl groups at the end of terminal
alkyne (R2) proceeded smoothly to afford the corresponding
products 2l and 2m in acceptable yields. The reaction was also
tolerant of various electron-deficient and electron-rich
aromatic groups, including Me, OMe, Cl, and CN at
substituted aryl groups and aliphatic groups to afford the
desired products 2n−s in moderate to good yield. Notably,
substrate N-methyl-N-(4-methyl-2-(phenylethynyl)phenyl)-3-
phenylpropiolamide 1t and N-(4-chloro-2-(phenylethynyl)-
phenyl)-N-methyl-3-phenylpropiolamide 1u still showed high
reactivity, enabling their conversion into products 2t and 2u in
high yields.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b02883.
■
S
Descriptions of experimental procedures and analytical
characterization (PDF)
Accession Codes
CCDC 1865953 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.
As shown in Scheme 3, the 18O-labeled control experiment
was performed to understand the mechanism for this tandem
Scheme 3. Control Experiments and Possible Mechanisms
AUTHOR INFORMATION
Corresponding Authors
■
*E-mail: srj0731@hnu.edu.cn.
*E-mail: jhli@hnu.edu.cn
ORCID
Ren-Jie Song: 0000-0001-8708-7433
Jin-Heng Li: 0000-0001-7215-7152
Author Contributions
§X.-H.O. and F.-L.T. contributed equally to this work.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the Natural Science Foundation of China (Nos.
21402046, 21625203, and 21472039), the Jiangxi Province
Science and Technology Project (Nos. 20171BCB23055,
20171ACB21032, 20171ACB20015, and 20165BCB18007),
and the Jiangxi Educational Committee Foundation of China
(No. GJJ160725) for financial support.
cyclization. When 4 equiv of H218O was added to the reaction
medium, the amount of 18O in the product 2a-18O was
obviously increased, which suggested that the newly formed
oxygen atom came from water.
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