Synthesis of 3-(2-quinolyl) chromones from ynones and quinoline: N -oxides via tandem reactions under transition metal- And additive-free conditions

Article abstract of DOI:10.1039/c9cc09460a

A novel method for the synthesis of 3-(2-quinolyl) chromones through a tandem [3+2] cycloaddition/ring-opening/O-arylation from ynones and quinoline N-oxides has been developed. This protocol proceeds under transition metal- and additive-free conditions a

Full text of DOI:10.1039/c9cc09460a

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DOI: 10.1039/C9CC09460A
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COMMUNICATION
Tandem reaction to 3-(2-quinolyl) chromones from ynones and
quinoline N-oxides under transition metal- and additive-free
conditions
Received 00th January 20xx,
Accepted 00th January 20xx
Jing Liu, Dan Ba, Yanhui Chen, Si Wen, and Guolin Cheng,*
DOI: 10.1039/x0xx00000x
www.rsc.org/
A novel method to synthesis of 3-(2-quinolyl) chromones through a
tandem [3+2] cycloaddition/ring-opening/O-arylation from ynones
and quinoline N-oxides has been developed. This protocol proceeds
under transition metal- and additive-free conditions and can be
amplified to gram level in 91% yield. 3-(1-isoquinolyl) and 3-(2-
pyridyl) chromones are also successfully synthesized using
isoquinoline and pyridine N-oxides under basic conditions. Various
heteroarene-contaning chromones were afforded in 30-98% yields,
which are difficult to be obtained and are compounds of interest in
pharmaceutical chemistry and chemical biology.
A
Transition metal-catalyzed annulation to 2,3-diaryl chromones
O
O
O
R1
R2
H
M
R1
R2
+
OH
Miurai, 2008, M = Rh
Yoshikai, 2016, M = Co
Gogoi, 2016, M = Ru
B
Transition metal-catalyzed three-component reaction to 2,3-diaryl chromones
O
R1
Br
R2
Pd, CO( 10 bar)
R1
+
Wu, 2016
O
O
R2
O
F
R1
R2
Ir, CO( 20 bar)
Wu, 2017
R1
R2
+
OH
O
Chromones are widely distributed in nature, and are used as
bactericides, antioxidants, and drugs due to their remarkable
biological properties. The increasing incidences of tumor,
C
Intramolecular Ullmann-type O-arylation to 2-substituted chromones
O
O
O
R1
R1
1
R2
Pd, Cu, or base
R2
X
O
malarial, bronchial, and pneumonia diseases have stimulated
X = F, Cl, Br, or OMe
2
the preparation of chromone-based drugs. Although
D
This work: tandem [3+2] cycloaddition/ring-opening/O-arylation
multitudinous synthetic protocols have been developed for the
R3
R3
3
,4
O
O
synthesis of chromones, there are few methods to access the
R1
R1
toluene
+
N
3
-aryl chromones, which are of vital importance because they
R2
N
O
F
O
R2
5
possess increased biological activities. The palladium-catalyzed
Suzuki and Stille couplings of 3-iodochromones with aryl Scheme 1 Methods for the synthesis of 3-(hetero)aryl chromone derivatives
boronic acids or aryl stannanes are the commonly used
6
,7
methods for the synthesis of 3-aryl chromones. The preparing
In the past decade, the intramolecular O-arylation through
1
0
of nucleophilic coupling partners such as heteroaryl boronic transition metal-catalyzed Ullmann reaction
acids and stannanes is challenging. The oxidative [4+2] promoted nucleophilic aromatic substitution (S Ar) have been
or base-
1
1
N
cycloaddition of salicylaldehydes and internal alkynes using well developed to access 2-substituted chromones (Scheme 1C).
8
a
8b
8c
Rh, Co, Ru, represents an attractive route to 2,3-diaryl However, transition-metals or strong bases are commonly
chromones (Scheme 1A). Recently, Wu and co-workers required. Thus, the development of new transition metal- and
reported the transition metal-catalyzed three-component additive-free synthetic method that addresses the
reactions for the assembly of 2,3-diaryl chromones (Scheme aforementioned shortcoming would therefore offer new
9
1
B). However, those synthetic methods are not transferable to opportunities to incorporate heteroaryl chromones into drug
heteroaryl substituted substrates, probably due to the strong candidates.
coordinative properties of heteroarenes.
Recently, we have discovered a base-promoted Michael
addition/Smiles rearrangement/N-arylation cascade reaction
for the synthesis of 1,2,3-trisubstituted 4-quinolones from
College of Materials Science & Engineering, Huaqiao University, Xiamen 361021,
China. E-mail: glcheng@hqu.edu.cn
1
2a
ortho-holagenphenyl ynones. In our sustaining interest in
1
2
†
Footnotes relating to the title and/or authors should appear here.
ynones chemistry, herein, we report a novel and efficient
method for the synthesis of 3-heteroaryl chromones through
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
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Journal Name
tandem [3+2] cycloaddition/ring-opening/O-arylation reaction ynone, an excellent yield of product was obtained (3h, 98%).
View Article Online
DOI: 10.1039/C9CC09460A
from easily obtained ynones and heteroarene N-oxides These results indicated that the reactivity was not sensitive to
Scheme 1D).13 While this work was under review, an elegant the electronic properties of R . Importantly, the ynone with n-
2
(
work was reported by Wang, in which 3-(2-quinolyl) chromones butyl and cyclopropyl groups could give the products in 56% and
were synthesized via acid-mediated cascade reaction of 87% yields, respectively (3i and 3j). The target product was
quinoline N-oxides with ortho-hydroxyphenyl ynones.1
4
afforded in a poor yield (3k, 30%), when R was a t-butyl group,
2
Our study was initiated by employing 1-(2-fluorophenyl)-3- probably because of the increased steric hindrance.
phenylprop-2-yn-1-one 1a and quinoline N-oxide 2a as the Remarkably, the presence of halogen (F) on the aroyl moiety of
model substrates to screen the reaction parameters. The ynone was well tolerated (3l, 76%), which makes this reaction
reaction was conducted using 1a (0.1 mmol), 2a (0.15 mmol), particularly attractive for further transformation. Ynone with an
and DMF (0.5 mL) at 120 °C under air for 12 h to afford the electron-withdrawing group on the aroyl moiety could also
desired chromone product 3a in 90% yield. The effect of the deliver the corresponding product (3m) in 72% yield. However,
solvent was subsequently investigated, and other solvents, such a complex mixture was obtained and the desired product (3n)
as CH
3
CN, tert-butanol, DCE, and 1,4-dioxane, all could give 3a was formed in a trace amount using ynone with an electron-
in good yields. 92% yield of 3a could be obtained using toluene, donating group as substrate.
and no product was observed when water was used as solvent.
We next turned our attention to investigation of the scope of
Then, the optimal conditions were identified as 1a (0.1 mmol), quinoline N-oxides for this transformation. Quinoline N-oxides
2
a (0.15 mmol), and toluene (0.5 mL) at 120 °C under air for 12 with different functional groups were investigated under the
h.
standard reaction conditions using ynone 1a as the coupling
With the optimized protocols in hand, we firstly investigated partner (Scheme 3). In general, quinoline N-oxides bearing both
the scope of ynones (Scheme 2). Having proved the perfect electron-donating substituents and electron-withdrawing
matching of this reaction system with a range of ynone substituents all could give the desired products in moderate to
derivatives, the desired chromone products were afforded in excellent yields (4a−j). Remarkably, halogen group (Br) and
2
3
0%-98% yields (3a−k). Ynones possessing halogens on R could electron-donating group (methyl) at the C3-position of the
furnish the corresponding chromone derivatives (3b) and (3c) in quinoline N-oxides were well tolerable, affording the
good yields (86% and 78%). In addition, the electron-donating corresponding product in good yields (4a and 4b, 62% and 60%),
2
groups (methyl, n-propyl, and methoxyl) on R for the which suggested that the steric hindrance on the quinoline N-
corresponding ynones could also afford the target products in oxides had a significant effect. The structure of 4a was
8
2%, 80%, and 84% yields, respectively (3d, 3e, and 3f). unambiguously
confirmed
by
single-crystal
X-ray
Similarly, meta-fluoro substituted substrate also could afford crystallography. Halogen group (Cl) on the 4-position of the
the desired product in 82% yield (3g). On the other hand, the quinoline ring could lead this reaction system in 76% yield (4c).
reaction was conducted by using heteroarene-substituted
On the other hand, the target product could be afforded in
excellent 94% yield from 4-methyl quinoline N-oxide (4d). The
electron-donating groups (methyl and methoxyl) at the
O
R1
toluene
20 oC, 12 h
O
R1
1
N
R2
+
N
O
F
R2
O
O
O
R
1a-1n
2a, 1.5 equiv
3a-3n
toluene
120 oC, 12 h
N
+
R
N
O
O
F
O
O
O
O
O
N
N
N
1a
2b-2o
4a-4j
O
Cl
N
F
Cl
Br
Me
O
O
O
3
a, 92%
3b, 86%
3c, 78%
N
N
O
O
O
O
O
O
N
N
N
O
O
O
3f, 84%
O
4a, 62%
4b, 60%
4c, 76%
Me
N
nPr
Me
OMe
Br
Me
3
d, 82%
3e, 80%
O
O
O
O
O
N
N
N
N
O
O
O
N
N
S
N
F
O
O
O
4d, 94%
4e, 88%
4f, 86%
NO2
OMe
O
3
g, 82%
3h, 98%
3i, 56%
O
O
O
O
O
5
R1
N
R
N
N
6
N
O
O
O
O
O
7
O
8
R = Me, 4i, 86%
R = OBn, 4j, 88%
4
g, 86%
4h, 76%
R1 = 5-F, 3l, 76%
3
j, 87%
3k, 30%
R1 = 7-CF3, 3m, 72%
R1 = 7-MeO, 3n, trace
Scheme 3 Scope of the N-oxides.
Scheme 2 Scope of the ynones
2
| J. Name., 2012, 00, 1-3
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COMMUNICATION
Conditions C or D
C6-position of the quinoline N-oxide also could afford the
desired products 4f and 4g both in higher yield (86%),
comparing to electron-withdrawing group (Br, 4e, 88%).
Introduction of a nitro group at the C6-position led to a slightly
lower yield (4h, 76%). The methyl and benzyloxyl groups at the
C8-position could afford the target products in good yields (4i
and 4j, 86% and 88%).
a)
b)
1a, 5 mmol
+
2a, 1.5 equiv
C : toluene, 120 oC, in sealed tube,
D : toluene, reflux, in flask with a condenser, 3a, 1.61 g, 92%
View A 3r at icle Online
DOI: 10.1039/C9CC09460A
3a, 1.59 g, 91%
O
O
O
R3
toluene
20 oC, 12 h
R1
R2
1
R1
+
R2
N
O
R3
NH
1
2, 1.5 equiv
5
Inspired by these exciting results, we further investigated the
effect of the X substituent on the aroyl moiety of the ynones
R1 = R = Ph, R3 = H,
1
5a, 90%
R1 = R1 = Ph, R3 = 4-Me,
R1 = R1 = Ph, R3 = 8-Me,
R1 = R1 = 4-FC6H4, R3 = H, 5b, 85%
R1 = R1 = 4-MeC6H4, R3 = H, 5c, 48%
5e, 55%
5f, 60%
(Scheme 4). However, poor yields were observed when the
R1 = R1 = Ph, R3 = 4-Cl,
R1 = 2-ClC H , R2 = Ph, R3 = H, 5g, 69%
5d, 45%
6
4
fluoro group was replaced by chloro, bromo, and methoxyl
groups (Scheme 4, Condition A). To our delight, good yields
could be obtained when the reaction was conducted under
basic conditions (Scheme 4, Condition B). Subsequently,
chromones 3o and 3p were synthesized in good yields from
ortho-chloro aroyl ynones. In addition, the desired products
could be afforded in 43-75% yields by using isoquinoline N-
oxide as the substrates (4k−m). Significantly, the reaction also
proceeded and the desired product 4n was afforded in 34%
yield by using pyridine N-oxide as the substrate.
A gram-scale conversion was performed using 1a and 2a as
substrates, and excellent isolated yields of 3a were obtained,
indicating the practicality of this method (Scheme 5a). To
explore the mechanistic hypothesis, control experiments were
performed. The reaction of ynones 1 and quinoline N-oxides 2
could give the 1,3-dione products (5a−g) in 45-90% yields under
the standard conditions (Scheme 5b). Subsequently, the
intermediate 6 was independently synthesized in 80% yield
from ynone 1a and quinoline N-oxide 2a, and the target product
F
O
O
toluene
Ph
120 oC, 12 h
H2O, reflux
3a, 99%
c)
1a
+
2a, 2 equiv
NH
6, 80%
Scheme5 Gram-scale reaction and control experiments.
O
OH
R3
O
R1
O
R1
R1
H
R2
N
O
R3
2
N
R2
N
R2
O
F
F
ring-opening
[
3+2] cycloaddition
F
B
R3
1
A
toluene, 120 o
C
intramolecular
cyclization
O
O
R3
R1
O
OH
O
R2
R1
R3
R1
N
rearomatization
N
NH
F
R2
O
R2
F
R3
-HF
6
3
C
Scheme 6 Possible reaction mechanism
3
a was afforded in 99% yield from intermediate 6 (Scheme 5c).
R3
On the basis of the experimental results and literature
O
R3
O
R1
R1
11,13
reports,
the reaction mechanism was proposed as shown in
Scheme 6. Initially, the base-promoted regioselective [3+2]
cycloaddition of ynone 1 and quinoline N-oxide 2 affords
intermediate A. Then, a ring-opening process of intermediate A
by N−O bond cleavage generates the key enol intermediate B,
which then is reversibly converted to 1,3-dione 6. Subsequently,
the species C is formed via intramolecular cyclization of B.
Finally, rearomatization of C by elimination of HF provided
chromones 3 (Scheme 6).
Condition A
Condition B
N
R2
+
N
O
R2
X
O
2
1
3 or 4
O
Condition Aa
Condition Bb
X=F, 89%
X=Cl, 75%
X=Br, 87%
X=OMe, 10%
N
X=F, 91%
X=Cl, 12%
X=Br, 16%
X=OMe, 5%
O
3a, 91%
O
O
O
O
O
In summary, we have developed a general and practical
strategy for the synthesis of 2,3-disubstituted chromone
derivatives through regioselective [3+2] cycloaddition, ring-
opening, and O-arylation cascade reaction from ynones and N-
oxides. This transition metal-free protocol can be completed in
one step with construction of one C−C bond and two C−O
bonds. The successful incorporation of heteroaryl groups into
chromone cores makes this method highly important in drug
discovery.
N
N
N
Cl
O
Cl
a
b
a
b
a
b
X = Cl, 3o, 5% , 89%
X = Cl, 3p, 6% , 79%
Br
X = F, 4k, trace , 50%
Me
Br
O
O
O
O
O
O
N
N
N
a
b
X = F, 4m, trace , 43%
a
b
X = F, 4n, tracea, 34%b
X = F, 4l, trace , 75%
This work was supported by the NSF of China (21672075) and
the Instrumental Analysis Center of Huaqiao University.
Scheme 4 Scope of the ynones and N-oxides. a Condition A: 1 (0.1 mmol), 2 (0.15 mmol),
toluene (0.5 mL) at 120 °C under an air atmosphere for 12 h. b Condition B: 1 (0.1 mmol),
2
h.
3 4
(0.15 mmol), Na PO (0.2 mmol), DMF (0.5 mL) at 100 °C under air atmosphere for 12
Conflicts of interest
There are no conflicts to declare.
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Journal Name
P. Sun, S. Gao, C. Yang, S. Guo, A. Lin and H. YVaieow, AOrtricgle.OLnelitnte.
Notes and references
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