An unprecedented tandem annulation of ω-azido-1-alkynes with diaryl-iodonium salts: A facile synthesis of polycyclic quinolines

Article abstract of DOI:10.1055/s-0034-1379248

Polysubstituted quinolines are synthesized through an unprecedented cascade annulation of ω-azido-1-alkynes with diaryliodonium salts, which serve as C2-building blocks. The reaction proceeds smoothly and is catalyzed by Cu(I) catalysts to give various qu

Full text of DOI:10.1055/s-0034-1379248

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cluster
An Unprecedented Tandem Annulation of ω-Azido-1-alkynes with Diaryl-
iodonium Salts: A Facile Synthesis of Polycyclic Quinolines
Polycyclic Quinolines
Junjie Chen,a Chao Chen,*a Jing Chen,a,b Hongpeng Gao,a Hongmei Qub
a
Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua
University, Beijing 100084, P. R. of China
E-mail: chenchao01@mails.tsinghua.edu.cn
b
School of Chemical Engineering, Tianjin University, Tianjin 300072, P. R. of China
Received: 14.08.2014; Accepted after revision: 15.09.2014
reported an efficient method to synthesize polycyclic
Abstract: Polysubstituted quinolines are synthesized through an
quinolines with diaryliodonium salts and ω-cyano-1-
unprecedented cascade annulation of ω-azido-1-alkynes with dia-
alkynes, which are readily accessible linear molecules
ryliodonium salts, which serve as C2-building blocks. The reaction
proceeds smoothly and is catalyzed by Cu(I) catalysts to give vari-
(Scheme 1, eq. 1).5
ous quinolines in good isolated yields with simple operation under
mild conditions.
O
O
N
N
Key words: quinolines, azides, alkynes, copper catalyst, tandem
annulation
N
N
O
Et
OH
O
luotonin A (1)
Polycyclic quinolines are privileged scaffolds in many
bioactive natural products and synthetic therapeutic
agents, exemplified by the natural topoisomerase I inhib-
itors luotonin A (1) and camptothecin (2) with structures
typical of pentacyclic quinoline (Figure 1).1 Moreover, ta-
crine, a tricyclic quinoline (under the trade name of
Cognex) was the first approved drug for the treatment of
camptothecin (2)
NH2
N
tacrine (3)
Alzheimer’s disease as a centrally acting anticholinester- Figure 1 Luotonin A (1), camptothecin (2) and tacrine (3)
ase and indirect cholinergic agonist.2 Therefore, the de-
Diaryliodonium salts, Ar2I+X– have recently received con-
siderable attention because of their use in the arylation of
a wide range of nucleophiles to synthesize valuable aro-
matic compounds.6 Our recent findings demonstrated that
diaryliodonium salts could be used as C2 building blocks
in organic reactions, and we disclosed their wider applica-
tion in the synthesis of arenes and heteroarenes.7 As a part
of our ongoing project, herein, we would like to report a
novel method to synthesize polycyclic quinolines through
velopment of new approaches toward polycyclic
quinolines is highly desired in synthetic chemistry. Many
methods have been developed for the construction of
quinoline derivatives, which involve the classical Miller,
Combes,
Conrad–Limpach–Knorr,
Niementowski,
Pfitzinger, and Friedlander reactions, and also more re-
cent approaches.3 Among these methods, probably only
Niementowski and Friedländer reactions are generally
suitable to construct polycyclic quinolines.4 Recently, we
R
N
N
R
R
Cu(OTf)2
– ArI
(1)
I
I
+
+
n
n
X
X
X
N
R
N3
R
R
Cu catalyst
– ArI
(2)
n
n
X
1
2: n = 1
4: n = 2
6: n = 3
3: n = 1
5: n = 2
7: n = 3
Scheme 1
SYNLETT 2014, 25, 2721–2726
Advanced online publication: 17.10.2014
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0034-1379248; Art ID: st-2014-w0677-c
© Georg Thieme Verlag Stuttgart · New York

2722
J. Chen et al.
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Br
Br
n-BuLi
NaN3
N3
Br
Ph
H
–78 °C
0.5 h
HMPA
overnight
Ph
Ph
2a
H2
C
N
N3
Cu(I)
– ArI
I
+
Ph
Ph
1a
2a
3aa
N
N
Cu(I) = Cu2O, 75%
Cu(I) = CuBr, 58%
N
Ph
8
Scheme 2 The synthesis of starting material 2a and its reaction with 1a
an unprecedented cascade annulation of ω-azido-1- ed in 58% yield. However, with Cu(OTf)2 (10 mol%) as
alkynes with diaryliodonium salts, which also served as the catalyst, dipolar cycloaddition product 8 was obtained
C2 building blocks (Scheme 1, eq. 2).
as the major product (48%).10 When 8 was isolated and
then treated with 1a and Cu2O under the standard condi-
tions for a further 8 h, no quinoline product was detected,
and the triazole was found to decompose.
We first examined the reaction of diphenyliodonium tri-
flate (1a) with ω-azido-1-phenyl-1-hexyne (2a), which
was easily prepared by an azidation reaction followed by
an ethynylation reaction of 1,4-dibromobutane (Scheme Inspired by this result, diphenyliodonium salts 1, with a
2; for details, see the Supporting Information). The reac- range of substituents, were further examined in the reac-
tion of 1a with 2a proceeded smoothly when catalyzed by tion with 2a; all worked well to give expected fused quin-
Cu2O (10 mol%) in 1,2-dichloroethane (DCE) at 60 °C to olines (2,3-dihydro-1H-cyclopenta[b]quinoline; Scheme
give five-membered-ring fused quinoline 3aa (4-phenyl- 3). The reaction of diphenyliodonium salts 1 with para-
2,3-dihydro-1H-cyclopenta[b]quinoline) in 75% isolated substituents including 4-methyl, 4-chloro, 4-bromo, 4-tri-
yield;8 where two hydrogen atoms of the azido methylene fluoromethyl, and 4-methoxycarbonyl groups provided
group were lost during the reaction.9 When Cu2O was re- fused quinolines 3ba–fa in higher yields than substrates
placed by CuBr (10 mol%) as the catalyst, 3aa was isolat- with an ortho-substituent (3ga). A mixture of regioiso-
R2
H2
C
Cu(I) (15 mol%)
N
R2
R2
N3
I
+
DCE , 60 °C
– ArI
R1
2a: R1 = Ph
2b: R1 = 4-MeOC6H4
2c: R1 = Bu
R1
1
3
N
N
N
N
N
Br
F3C
Cl
Me
Ph
Ph
Ph
3ca, 74% (Cu2O)
Ph
Ph
3aa, 75% (Cu2O)
3ba, 59% (Cu2O)
3ea, 63% (Cu2O, 80 °C)
3da, 72% (CuI)
N
N
Me
N
MeOOC
:
Me
Ph
Ph
Ph
3fa, 75% (Cu2O, 60 °C)
3ha + 3ha',68% (Cu2O, 1:1)
F
N
N
N
Bu
3ac, 67% (Cu2O)
C6H4-4-OMe
Ph
3ga, 44% (CuI, 80 °C)
3ab, 44% (Cu2O, 80 °C)
Scheme 3 The synthesis of 2,3-dihydro-1H-cyclopenta[b]quinoline 3 from the reaction of 1 and ω-azido-1-hexyne
Synlett 2014, 25, 2721–2726
© Georg Thieme Verlag Stuttgart · New York

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Polycyclic Quinolines
2723
H2
C
R
Cu(I)
(15 mol%)
N
N3
R
R
+
I
– ArI
DCE, 60 °C
Ph
Ph
1
4a
5
N
N
N
N
N
Cl
Me
N
F
Br
Ph
Ph
Ph
5ba 41% (Cu2O)
Ph
Ph
5aa, 67% (CuI)
5ca, 65% (Cu2O)
5da, 77% (Cu2O)
5ea, 82% (Cu2O)
F
N
Me
N
N
F3C
:
Ph
5fa, 68% (CuI)
Me
Ph
Ph
Ph
5ia, 39% (Cu2O, 80 °C)
5ha + 5ha', 69% (Cu2O, 1:1)
Scheme 4 The synthesis of tetrahydroacridine 5 from the reaction of 1 and 4a
mers 3ha/3ha′ (ratio 1:1) was obtained when di(m-
tolyl)iodonium salt was used. ω-Azido-1-anisol-1-hexyne
(2b) and ω-azido-5-decyne (2c) also reacted with di-
phenyliodonium (1a) and afforded the corresponding
products 3ab and 3ac in satisfactory yields.
Encouraged by the successful preparation of five-mem-
bered-ring fused quinolines, we next examined the prepa-
ration
of
their
six-membered
counterparts
(tetrahydroacridine) by using diaryliodonium salts and ω-
azido-1-heptyne 4a, which was easily prepared as de-
scribed for 2a with a similar method (Scheme 4). Di-
phenyliodonium (1a) reacted with ω-azido-1-heptyne 4a
to give fused quinoline 5aa in 67% isolated yield.11 The
reaction of diphenyliodonium salts 1 with para-substitu-
ents including 4-methyl, 4-fluoro, 4-chloro, 4-bromo, and
4-trifluoromethyl groups provided fused quinolines 5aa–
fa in higher yields than obtained with an ortho-substituted
substrate (5ia). A mixture of regioisomer 5ha/5ha′ (ratio
1:1) was obtained when di(m-tolyl)iodonium salt was
used. Besides characterization by NMR and MS, the
Figure 2 Single-crystal structure of 5ea
structure of 5ea was unambiguously confirmed by XRD
analysis (Figure 2).12
Finally, we prepared seven-membered-ring fused quino-
lines
(7,8,9,10-tetrahydro-6H-cyclohepta[b]quinoline,
H2
C
Cu(I)
(15 mol%)
R
N3
N
R
R
+
I
– ArI
DCE , 60 °C
Ph
Ph
1
6a
N
N
N
N
Cl
Me
F
Ph
Ph
Ph
Ph
7ca, 74% (Cu2O)
7aa, 72% (CuI)
7ba, 54% (Cu2O)
7da, 64% (Cu2O)
F
N
N
N
Br
F3C
Ph
7ia, 52% (Cu2O, 80 °C)
Ph
Ph
7ea, 57% (Cu2O)
7fa, 67% (CuI)
Scheme 5 The synthesis of 7,8,9,10-tetrahydro-6H-cyclohepta[b]quinoline 7 from the reaction of 1 and 6a
© Georg Thieme Verlag Stuttgart · New York
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J. Chen et al.
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Cu(III)
Cu(I)
I
1a
H
H
H
N
N N
N
N
N
N
N
N
Ph
Ph
Ph
2a
– N2
H
H
N
N
N
N
H
– 2[H]
Ph
H+
Ph
Ph
Ph
I
3aa
II
III
Scheme 6 A mechanistic proposal for the reaction of 1a and 2a
NH2
Me
Me
I
Ph
+
N
Me
N3
H2O
1a
Cu(I)
O
Ph
Ph
Ph
8
9
10
Scheme 7 Indirect evidence for the proposed pathway
Scheme 5) by using diaryliodonium salts and ω-azido-1- but imine 9 and oxo-alkyne 10 was observed after the
octyne 6a, which was easily prepared as described for 2a. mixture was hydrolyzed (Scheme 7).
Diphenyliodonium 1a reacted with ω-azido-1-octyne 6a
In conclusion, we have developed a concise construction
of polycyclic quinolines through tandem annulation of ω-
azido-1-alkynes with diaryliodonium salts. The process
to give fused quinoline 7aa in 72% isolated yield.13 The
reaction of diphenyliodonium salts 1 with para-substitu-
ents including 4-methyl, 4-fluoro, 4-chloro, 4-bromo, and
produces polycyclic quinolines in one step with readily
4-trifluoromethyl groups provided fused quinolines 7aa–
available, linear staring materials and catalyst. Interest-
ingly, diaryliodonium salts with Cu catalyst initiated the
electrophilic attack on the azido group and served as a C2
fa in higher yields than obtained with ortho-substituted
substrate 7ia.
It was reported that alkyl azides reacted with electrophiles unit in the products. Moreover, an azido methylene moi-
to generate electrophilic species upon N2 elimination.9 ety was transferred into the -N=C- moiety of the product,
Therefore, a similar process likely takes place in our case and two hydrogen atoms were removed from the struc-
to give intermediate I when ω-azido-1-alkyne (exempli- ture. Further design and synthesis of bioactive and natural
fied as 2a) reacts with a phenyl cationic species, which is molecules with this new strategy are in progress.
presumably generated from diphenyliodonium salt and
copper catalyst (Scheme 6).14 Intermediate I is naturally
Acknowledgment
phenyl iminium salt and chemically equal to intermediate
This work was supported by National Natural Science Foundation
of China (21102080, 21372138) and Tsinghua University Initiative
Scientific Research Program (2011Z02150).
II. Intermediate II easily undergoes electrophilic cycliza-
tion to give quinoline backbone III, resembling a classic
15
Povarov reaction. The dehydrogenation-aromatization
of intermediate III would give the product 3aa. As indi-
rect evidence for this pathway, when azido-1-alkyne 8
was reacted with 1a, no quinoline derivative was observed at
Supporting Information for this article is available online
http://www.thieme-connect.com/products/ejournals/journal/
10.1055/s-00000083.SunogIpimrfiantoSuIpg
n
fonirtat
ori
Synlett 2014, 25, 2721–2726
© Georg Thieme Verlag Stuttgart · New York

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Polycyclic Quinolines
2725
reaction mixture was stirred at 60 °C for 24 h, and then
poured into a mixture of sat. aq NaHCO3 (5 mL) and CH2Cl2
(20 mL). The organic phase was separated, washed with sat.
aq NaHCO3 (2 × 5 mL), and then dried over anhydrous
Na2SO4. Evaporation of the solvent followed by purification
on silica gel provided 9-phenyl-2,3-dihydro-1H-
References and Notes
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9-Phenyl-2,3-dihydro-1H-cyclopenta[b]quinoline (3aa):
1H NMR (400 MHz, CDCl3): δ = 8.07 (dd, J = 8.8, 1.0 Hz,
1 H), 7.66–7.58 (m, 2 H), 7.56–7.42 (m, 3 H), 7.42–7.32 (m,
3 H), 3.24 (t, J = 7.7 Hz, 2 H), 2.91 (t, J = 7.4 Hz, 2 H), 2.17
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167.68, 148.1, 142.8, 136.9, 133.8, 129.4 (2×CH), 129.0,
128.6 (2×CH), 128.4, 128.1, 126.3, 125.8, 125.6, 35.4, 30.5,
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(11) Preparation of 5aa; Typical Procedure: 7-Azido-1-
phenyl-1-heptyne (4a; 0.3 mmol, 63.9 mg) was added to a
solution of diphenyliodonium trifluoromethanesulfonate
(1a; 0.6 mmol, 258 mg) and Cu2O (0.045 mmol, 6.5 mg) in
anhydrous DCE (2.0 mL) under a N2 atmosphere. The
reaction mixture was stirred at 60 °C for 24 h, and then
poured into a mixture of sat. aq NaHCO3 (5 mL) and CH2Cl2
(20 mL). The organic phase was separated, washed with sat.
aq NaHCO3 (2 × 5 mL), and then dried over anhydrous
Na2SO4. Evaporation of the solvent followed by purification
on silica gel provided 9-phenyl-1,2,3,4-tetrahydroacridine
(5aa; 52 mg, 67% isolated yield) as a yellow solid. This
product has been reported5 previously.
9-Phenyl-1,2,3,4-tetrahydroacridine (5aa): 1H NMR (400
MHz, CDCl3): δ = 8.02 (d, J = 8.5 Hz, 1 H), 7.60 (ddd, J =
8.3, 5.1, 3.1 Hz, 1 H), 7.55–7.42 (m, 3 H), 7.35–7.27 (m,
2 H), 7.23 (dd, J = 8.0, 1.4 Hz, 2 H), 3.20 (t, J = 6.6 Hz, 2 H),
2.60 (t, J = 6.5 Hz, 2 H), 2.02–1.88 (m, 2 H), 1.84–1.70 (m,
2 H). 13C NMR (101 MHz, CDCl3): δ = 159.2, 146.6, 146.4,
137.3, 129.2 (2×CH), 128.7 (2×CH), 128.5, 128.5, 127.8,
126.8, 125.9, 125.5, 34.4, 28.2, 23.2, 23.1. GC-MS: m/z
calcd for C19H17N: 259; found: 259.
(12) CCDC-1019165 (3da) contains the supplementary
crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge
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Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
(13) Preparation of 7aa; Typical Procedure: 8-Azido-1-
phenyl-1-octyne (6a; 0.3 mmol, 68.1 mg) was added to a
solution of diphenyliodonium trifluoromethanesulfonate
(1a; 0.6 mmol, 258 mg) and Cu2O (0.045 mmol, 6.5 mg) in
anhydrous DCE (2.0 mL) under a N2 atmosphere. The
reaction mixture was stirred at 60 °C for 24 h, and then
poured into a mixture of sat. aq NaHCO3 (5 mL) and CH2Cl2
(20 mL). The organic phase was separated, washed with sat.
aq NaHCO3 (2 × 5 mL), and then dried over anhydrous
Na2SO4. Evaporation of the solvent followed by purification
on silica gel provided 11-phenyl-7,8,9,10-tetrahydro-6H-
cyclohepta[b]quinoline (7aa; 59 mg, 72% isolated yield) as
a yellow solid. This product has been reported5 previously.
11-Phenyl-7,8,9,10-tetrahydro-6H-
(8) Preparation of 3aa; Typical Procedure: 6-Azido-1-
phenyl-1-hexyne (2a; 0.3 mmol, 59.7 mg) was added to a
solution of diphenyliodonium trifluoromethanesulfonate
(1a; 0.6 mmol, 258 mg) and Cu2O (0.045 mmol, 6.5 mg) in
anhydrous DCE (2.0 mL) under a N2 atmosphere. The
cyclohepta[b]quinoline (7aa): 1H NMR (301 MHz,
CDCl3): δ = 8.03 (d, J = 8.3 Hz, 1 H), 7.60 (ddd, J = 8.3, 6.5,
© Georg Thieme Verlag Stuttgart · New York
Synlett 2014, 25, 2721–2726

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J. Chen et al.
CLUSTER
1.8 Hz, 1 H), 7.55–7.42 (m, 3 H), 7.36–7.27 (m, 2 H), 7.26–
7.19 (m, 2 H), 3.32–3.23 (m, 2 H), 2.73–2.66 (m, 2 H), 1.91–
1.77 (m, 4 H), 1.67–1.53 (m, 2 H). 13C NMR (76 MHz,
CDCl3): δ = 165.0, 146.0, 145.6, 137.8, 134.0, 129.6
(2×CH), 128.8, 128.6 (2×CH), 128.3, 127.8, 127.1, 126.5,
125.7, 40.4, 32.1, 30.9, 28.7, 27.2. GC-MS: m/z calcd for
C20H19N: 273; found: 273.
L.; Suero, M. G.; Gaunt, M. J. Angew. Chem. Int. Ed. 2013,
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