Carbonylative Sonogashira annulation sequence: One-pot synthesis of 4-quinolone and 4H-chromen-4-one derivatives

Article abstract of DOI:10.1016/j.tetlet.2018.04.029

Carbonylative Sonogashira annulation sequence for one pot synthesis of 4-quinolone and 4H-chromen-4-one has been developed in presence of Pd-NHC catalyst. Substituted 2-iodoaniline and 2-iodophenol independently underwent in the carbonylative Sonogashira

Full text of DOI:10.1016/j.tetlet.2018.04.029

Accepted Manuscript
Carbonylative Sonogashira annulation sequence: One-pot synthesis of 4-qui-
nolone and 4H-chromen-4-one derivatives
Prasanjit Ghosh, Aritra Kumar Nandi, Sajal Das
PII:
S0040-4039(18)30464-7
https://doi.org/10.1016/j.tetlet.2018.04.029
TETL 49892
DOI:
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
27 February 2018
9 April 2018
10 April 2018
Please cite this article as: Ghosh, P., Nandi, A.K., Das, S., Carbonylative Sonogashira annulation sequence: One-
pot synthesis of 4-quinolone and 4H-chromen-4-one derivatives, Tetrahedron Letters (2018), doi: https://doi.org/
10.1016/j.tetlet.2018.04.029
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Graphical Abstract
Carbonylative Sonogashira annulation
sequence: One-pot synthesis of 4-quinolone
and 4H-chromen-4-one derivatives
Leave this area blank for abstract info.
Prasanjit Ghosh, Aritra Kumar Nandi and Sajal Das
O
O
I
R1
H
R1
H
R
R
R1
O
R1
N
Z
H
Z = OH, -NH2
R1 = aromatic, aliphatic
14 examples
R1 = aromatic, aliphatic
8 examples
Broad Substrate scope
Ligandless coupling
CO gas free
50-94%
61-82%
Low catalyst loading

1
Tetrahedron Letters
Carbonylative Sonogashira annulation sequence: One-pot synthesis of 4-quinolone
and 4H-chromen-4-one derivatives
Prasanjit Ghosha, Aritra Kumar Nandia, and Sajal Dasa,*
aDepartment of Chemistry, University of North Bengal, Siliguri 734 013, India
ARTICLE INFO
ABSTRACT
Article history:
Received
Carbonylative Sonogashira annulation sequence for one pot synthesis of 4-quinolone and 4H-
chromen-4-one has been developed in presence of Pd-NHC catalyst. Substituted 2-iodoaniline
Received in revised form
Accepted
Available online
and 2-iodophenol independently underwent in the carbonylative Sonogashira annulation reaction
with a variety of acetylenes to result in 4-quinolone and flavone derivatives respectively in good
to excellent yield. Moreover, this protocol does not require toxic CO gas, high catalyst loading
and any expensive salt/additive. Herein we, for the first time, are using Mo(CO)6, as solid CO
source for the one pot synthesis of flavone derivatives via carbonylative Sonogashira annulation
reaction.
Keywords:
Pd-NHC
Carbonylative Sonogashira
4-quinolone
Flavone
Mo(CO)6
2009 Elsevier Ltd. All rights reserved.
Annulation reaction
1. Introduction
Venkataraman rearrangement11 for the preparation of chromone
derivatives are very popular to the chemists. However, these
4-quinolones are mainly occurred in many natural products
and bio-active molecules. 4-Quinolone moiety has wide
applications in the field of medicinal chemistry as a privileged
building unit.1 As a consequence, the synthesis of 4-quinolone
has remained a great interest and several procedures are available
in the literature.2 Generally, the most useful method is the
condensation of anilines with β-keto esters followed by the
cyclization of in situ formed β-amino acrylates. This reaction
became ineffective in the case of electro deficient anilines.3 Later
strategies are the heterocyclization of 2-amino chalcone4 and
carbonylation reaction of allenes with N-tosyl-o-iodo anilines.5
pathways possess various disadvantages like, harsh reaction
condition, multistep process, poor functional group tolerance and
formation of by-products. Use of Palladium, as a catalyst for the
synthesis of heterocycles, has been a profound arena of research
during past two decades.12
Recently, palladium catalysed cyclocarbonylation of aryl
halides, CO and a nucleophile became more attractive due to its
versatility and has been applied for the syntheses of multitude
arylcarbonyl derivatives (e.g.-ester, amide, acids and ketones).13
In addition, Palladium(0) catalysed multicomponent
cyclocarbonylation reaction of terminal acetylenes with 2-
iodophenol and 2-iodoaniline under elevated pressure of carbon
monoxide has been a general method for the synthesis of both
chromone14 and 4-quinolone5,15 derivatives. Genelot and his co-
workers used a two-step protocol to synthesize BILN-2061, a
serine protease inhibitor.16 Although, this method bears the use of
highly toxic, flammable, invisible and tasteless CO gas. In
addition, it requires special equipment for safe handling as well
as for maintaining the requisite pressure of CO gas. Lizuka et al.
developed a nongaseous carbonylative Sonogashira technique to
provide alkynones using Mo(CO)6 as CO source.17 Very recently,
Larhed et al. reported nongaseous carbonylative Sonogashira
annulation to prepare the 2-substituted 4-quinolone derivative
under microwave irradiation as well as room temperature
method.18 However, the method requires high loading of
palladium catalyst, expensive ligand (dppf) and salt. In 2016, Wu
et al. also reported a technique for the synthesis of flavone
derivatives via ligand free Pd/C catalysed cyclocarbonylation
reaction in excellent yields using carbon monoxide gas.19
Naturally occurring the chromone moiety and its derivatives
possessed diverse pharmaceutical6 and biological activities
(Figure-1).7 It also exhibits some interesting fluorescence
characteristics.8 Therefore, the development as well as
enrichment of the methods for their synthesis is an interesting
area of research in organic synthesis.
O
OH
O
OH
O
O
MeO
MeO
MeO
Me2N
O
HO
O
OH
Dimefline
Luteolin
Oroxylin A
OH
O
O
O
N
F
O
O
N
H
O
Efloxate
Antimitotic Antitumor Agents
Figure 1: Biologically active flavones and 4-quinolones
Three classical non-catalytic routes such as Kostanecki–
Robinson reaction,9 Claisen condensation10 and Baker–

2
Tetrahedron Letters
O
2. Results and discussion
Pd/L; CO (20 bar)
Et2NH, 120°C
Previous works
ref 15
N
H
R1
Our initial attempts to the carbonylative Sonogashira
O
O
annulation reaction between 2-iodoaniline with phenylacetylene
in presence of Mo(CO)6, as CO source, Pd(OAc)2 as catalyst at
95°C in DMF was unsuccessful even after 22 h of reaction (table
1; entry 1). Modest yield of the final product was obtained when
the reaction was carried out in presence of 5 mol% of Pd(PPh3)4.
The yield could be further increased on utilizing different variety
of palladium catalysts (table 1; entries 3, 4). A good yield (75%)
of compound 3a was observed within 15 h of reaction when 2
mol% of Pd-NHC catalyst was used (table 1; entry 4).
Pd(dppf)Cl2; CO (5 bar)
Et3N, 80°C; toluene
Et2NH, 2 h
R1
NH2
N
H
R1
I
+
ref 14c
R1
Z
O
Z = -NH2, -OH
Pd2(dba)3, dppf, Mo(CO)6, Et2NH
Cs2CO3, 120°C, MW, 20 min
ref 18
N
H
R1
O
Pd/C; CO (20 bar), toluene
Et2NH (2 equiv), 110°C
ref 19
O
R1
This work
O
I
Pd-NHC (2 mol%)
+
We next focused our attention for improving the yield of the
product, 2-phenyl 4-quinolone (3a), by changing the other
parameter like, base which often plays vital role in this kind of
reaction.15,18,19 In presence of inorganic bases like K2CO3;
Cs2CO3 as well as organic base like DBU, we observed
R1
Z
R1
Mo(CO)6, Me2NH, DMF
95°C, 15h
Z
Z = -NH, -O
22 examples
Z = -NH2, -OH
Figure 2: Palladium catalysed Carbonylative Sonogashira annulation
sequence and the methods developed till now
disappointing yield of the final compound 3a (Table 1, entries 5-
7). Surprisingly, in the presence of 4 equivalent of
Our group is actively working on the synthesis of
functionalized 4-quinolones and its further modification. 20 In our
previous reports, we accomplished to synthesize the highly
functionalized 6-aryl substituted-4-quinolones via regioselective
bromination followed by Suzuki cross-coupling reaction,20a nitro
derivatives of 4-quinolones via regio-controlled nitration at
ambient condition,20b and 3-aroyl-quinolin-4(1H)-one from 3-
iodo-quinolin-4(1H)-one using carbonylative Suzuki coupling
reaction.20c It has opened an avenue for the quest of newly
functionalized quinolone moieties. Herein, we report a
carbonylative Sonogashira annulation sequence (Scheme-1) for
the synthesis of both flavone and 4-quinolone scaffolds in the
presence of our pre-synthesized Pd-NHC catalyst21 where
Mo(CO)6 used as CO source. It is worth noting that both 2-
iodoaniline and 2-iodophenol derivatives are equally effective in
the carbonylative Sonogashira annulation reaction to result in 4-
quinolone and flavone respectively in good to excellent yield. To
the best of our knowledge, there is no example of CO-gas free
method for the synthesis of flavone via carbonylative
Sonogashira annulation reaction.
dimethylamine as base, the reaction between 2-iodoaniline and
phenylacetylene in DMF at 95°C was completed within 15 h and
a 94% yield of the product 3a was obtained upon isolation (table
1, entry 8). Comparing the same reaction at room temperature
resulted only 21% yield of the product 3a (Table 1, entry 9).
Later, we checked the other reaction parameters like reaction
time, temperature and catalyst loading for finalizing the optimal
reaction condition. When the reaction was carried out at 95°C for
10 h, we observed only 68% yield of the compound 3a (Table 1,
entry 10). A slight deviation of reaction conditions, like decrease
in reaction temperature or catalyst loading, with reference to the
condition given in table 1: entry 8, in both cases we observed the
low yield of the final compound 3a (Table 1, entry 11, 12). We
were unable to detect the product 3a when the same reaction was
performed in the presence of Fe3(CO)12 as carbonyl source (table
1, entry 13). In absence of palladium catalyst the reaction did not
proceed at all even after 15 h (Table 1, entry 14). Changing the
solvent system from DMF to toluene, no effective result was
obtained (Table 1, entries 15, 17). In anisole, the desired product
was formed but in lesser amount (Table 1, entry 16). Eventually,
the combination of Pd-NHC (2 mol%), Me2NH (4 equiv.),
Mo(CO)6 (2 equiv.) in DMF at 95°C, was found to be optimal
for the carbonylative Sonogashira annulation reaction between
2-iodoaniline and phenyl acetylene, leading to the 2-phenyl 4-
quinolone 3a in 94% yield after 15 h.
O
O
O
Pd-NHC (2 mol%)
Mo(CO)6, Me2NH
Pd-NHC (2 mol%)
Mo(CO)6, Me2NH
I
R
R
R1
N
H
R1
DMF, 15 h, 95°C
DMF, 15 h, 95°C
Z
H
R1
H
R1
R1 = aromatic, aliphatic
Z = -OH, -NH2
R1 = aromatic, aliphatic
8 examples
14 examples
50-94%
61-82%
Scheme 1: Our synthetic plan for both 4-quinolones and
flavones
Table 1: Optimization of reaction conditiona
O
I
+
NH2
N
H
2a
1a
3a
entry catalyst (mol %)
base
CO source
temp (°C) solvent
time (h)
yield (%)b
1
2
3
4
5
6
7
8
Pd(OAc)2 (5)
Pd(PPh3)4 (5)
PdCl2 (5)
Pd-NHC (2)
Pd-NHC (2)
Pd-NHC (2)
Pd-NHC (2)
Pd-NHC (2)
Pd-NHC (2)
Pd-NHC (2)
Et3N
Et3N
Et3N
Et3N
K2CO3
Cs2CO3
DBU
Me2NH
Me2NH
Me2NH
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
95
95
95
95
95
95
95
95
rt
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
22
20
20
15
15
15
15
15
15
10
ND
30
58
75
trace
41
ND
94
21
9
10
95
68

3
11
12
13
14
15
16
17
Pd-NHC (2)
Pd-NHC (1)
Pd-NHC (2)
-
Pd-NHC (2)
Pd-NHC (2)
Pd-NHC (2)
Me2NH
Me2NH
Me2NH
Me2NH
K2CO3
Et3N
Mo(CO)6
Mo(CO)6
Fe3(CO)12
Mo(CO)6
Mo(CO)6
Mo(CO)6
Mo(CO)6
80
95
95
95
95
95
95
DMF
DMF
DMF
DMF
Toluene
Anisole
Toluene
15
15
15
15
15
20
15
77
79
ND
ND
ND
45
Cs2CO3
ND
aReaction condition: 2-iodo aniline (0.25 mmol, 55mg), Phenyl acetylene (2 equiv, 0.50 mmol, 50 mg), Base (4 equiv.), Mo(CO)6 (2
equiv., 0.50 mmol, 132 mg), Solvent (2 ml) stirred at 95°C under N2 atm. bIsolated yield after column chromatography
After optimizing the reaction conditions, we next explored the
scope and the limitation of the carbonylative Sonogashira
annulation reaction. Accordingly, a variety of alkynes were
treated with differently substituted 2-iodoanilines under the
optimized conditions and the corresponding results are displayed
in table 2. Reaction between 2-iodoaniline and phenylacetylene
gave 94% of 2-phenyl 4-quinolone (3a). A comparable yield of
the final products [2-aryl 4-quinolone] were observed when
electron-donating group substituted phenylacetylenes were used
as coupling partner (3b-3d). Good yield of the product 3e was
observed upon the reaction between 2-iodoaniline and 1-
ethynylnapthalene. A slight decrease in yield of the final products
were observed when an electron withdrawing group present in
the phenylacetylene moiety (3f-3h). Presence of electro-
withdrawing group might decrease the nucleophilicity of terminal
alkynes. This was further proved when 2-iodoaniline was treated
with methyl propiolate, we did not isolate any expected product
after reaction (3j). In absence of electron-withdrawing group, an
aliphatic terminal acetylene was found equally effective in
Carbonylative Sonogashira reaction with 2-iodoaniline and
resulted in 70% yield of the desired product 3i. However, 5-
fluoro or chloro substituted 2-iodo anilines were successfully
coupled with alkynes to afford the desired 2-substituted 4-
quinolone derivatives in moderate yields (3k-3n).
conditions and afforded the corresponding chromone derivatives
5e and 5f in excellent yields. Both 3-methyl-but-1-yne and
ethynylcyclopropane were successfully participated in the
carbonylative Sonogashira annulation reactions with 2-
iodophenol to provide the corresponding chromone derivatives
5g and 5h in good yield.22
Table 3: Scope of terminal acetylenes in the carbonylative
Sonogashira coupling of 4H-chromen-4-one synthesisa
O
I
+
R
OH
O
R
4
2
5a-5h
O
O
O
O
O
O
O
O
5b, 80%b
5c, 73%b
5d, 72%b
5a, 82%b
O
O
O
O
O
O
O
O
O
Br
F
5g, 61%b
5h, 67%b
5e, 70%b
5f, 75%b
aReaction condition: 2-iodophenol (0.25 mmol, 55mg),
Substituted alkynes (0.5 mmol), Me2NH (4 equiv.), Mo(CO)6
(0.50 mmol, 132 mg), DMF (2 ml) stirred at 95°C under N2 atm.
bIsolated yield after column chromatography
Table 2: Scope of various terminal acetylenes and iodoaniline
in the carbonylative Sonogashira coupling of 4-quinolone
derivative synthesisa
Conclusions
In summary, we developed an operationally simple, ligand free
carbonylation reaction for the successful synthesis of biologically
active motifs such as 4-quinolones and flavones. Our protocol
avoids the use of toxic CO gas, high catalyst loading and use of
any expensive salt. Moreover, the cyclocarbonylation of both 2-
iodophenol and 2-iodoaniline with terminal alkynes was
excellent and the corresponding products were obtained in
moderate to excellent yield. Notably, this CO gas free synthesis
of flavones proceeds efficiently, and is the first documented
approach utilizing this method. Studies to expand this
O
I
NH2
R
R1
+
N
H
R1
R
2
1
3a-3n
O
O
O
O
O
N
H
N
H
N
H
N
H
N
H
O
3a, 94%b
3b, 74%b
3c, 83%b
3d, 78%b
3e, 72%b
O
O
O
O
O
carbonylative Sonogashira annulation reaction for the synthesis
of diverse functionalized 4-quinolone and flavone derivatives are
ongoing and will be reported soon in due course.
O
N
H
N
H
N
H
N
H
N
H
O
F
Br
O
Cl
3f, 71%b
3i, 70%b
3j, nr
3g, 63%b
3h, 65%b
O
O
O
Acknowledgements
Cl
N
H
F
N
H
Cl
N
H
F
N
H
3k, 53%b
3n, 55%b
3l, 59%b
3m, 50%b
We thank the SERB, New Delhi for financial support
(EMR/2016/001250). PG is thankful to UGC for his fellowship.
aReaction condition: 2-iodoaniline (0.25 mmol, 55mg),
Substituted alkynes (2 equiv, 0.50 mmol), Me2NH (4 equiv.),
Notes and references
Mo(CO)6 (0.50 mmol, 132 mg), Pd-NHC (2 mol%), DMF (2 ml)
stirred at 95°C under N2 atm. bIsolated yield after column
chromatography
1.
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reaction between 2-iodophenol (4) and phenyl acetylene under
the optimized condition and isolated the desired product 5a in
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electron rich aromatic acetylenes proceeded very well and gave
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flavones: A mixture of 2-iodo aniline/2-iodo phenol (0.25 mmol),
Pd-NHC (5 mg, 2 mol%), Mo(CO)6 (0.50 mmol, 132 mg) was
taken in round bottomed flask and backfilled with nitrogen three
times. Alkyne (0.50 mmol), DMF (2 ml) and Me2NH (4 equiv)
were added to the reaction mixture via syringe. The reaction
mixture was heated at 95°C until the completion of the reaction.
Afterwards, the reaction mixture was poured into the water and
extracted with ethyl acetate (3 X 10 ml). The organic phase was
dried over Na2SO4 and concentrated under reduced pressure. The
residue was purified through column chromatography using ethyl
acetate and petroleum ether as eluents.
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Supplementary Material
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Supplementary material that may be helpful in the review
process should be prepared and provided as a separate electronic
file. That file can then be transformed into PDF format and
submitted along with the manuscript and graphic files to the
appropriate editorial office.
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5
Highlights
 One pot synthesis of 4-quinolone and
4H-chromen-4-one
 Free from toxic CO gas and expensive
additives
 Low catalyst loading