Cubic nano-copper(I) oxides as reusable catalyst in consecutive decarboxylative C[sbnd]H arylation and carbonylation: rapid synthesis of carbonyl dibenzofurans

Article abstract of DOI:10.1016/j.tetlet.2016.09.074

Consecutive chemo- and regio-selective decarboxylative C[sbnd]H arylation, followed by carbonylative C[sbnd]C coupling of aryl halide with isocyanide/alcohol was applied for the first time in one-step synthesis of carbonyl dibenzofurans with nanodomain cuprous oxide under aerobic condition. As a proof of concept, several novel dibenzofurans were synthesized from 2-(3-iodophenoxy)benzoic acid in good yield. The tandem protocol eliminates the use of excess catalysts, hazardous organic solvents, heavy metals like palladium or rhodium, ligands, oxidants, or external additives. More importantly, the cubic Cu(I) nanocatalyst can be recovered and recycled for three consecutive reactions without any significant loss of catalytic activity or any change in its morphology. Use of water as solvent and reusable catalyst makes the reaction environment friendly.

Full text of DOI:10.1016/j.tetlet.2016.09.074

Accepted Manuscript
Cubic nano-copper(I) oxides as reusable catalyst in consecutive decarboxylative
C-H arylation and carbonylation: rapid synthesis of carbonyl dibenzofurans
Rammyani Pal, Nivedita Chatterjee, Manas Roy, Sabyasachi Sarkar, Swarbhanu
Sarkar, Asish Kumar Sen
PII:
S0040-4039(16)31255-2
DOI:
http://dx.doi.org/10.1016/j.tetlet.2016.09.074
TETL 48144
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
29 July 2016
16 September 2016
21 September 2016
Please cite this article as: Pal, R., Chatterjee, N., Roy, M., Sarkar, S., Sarkar, S., Sen, A.K., Cubic nano-copper(I)
oxides as reusable catalyst in consecutive decarboxylative C-H arylation and carbonylation: rapid synthesis of
carbonyl dibenzofurans, Tetrahedron Letters (2016), doi: http://dx.doi.org/10.1016/j.tetlet.2016.09.074
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Graphical Abstract
Cubic nano-copper(I) oxides as reusable catalyst in
consecutive decarboxylative C-H arylation and
carbonylation: rapid synthesis of carbonyl dibenzofurans
Rammyani Pal, Nivedita Chatterjee, Manas Roy, Sabyasachi Sarkar, Swarbhanu Sarkar and Asish Kumar Sen

1
Tetrahedron Letters
journal homepage: www.els evier.com
Cubic nano-copper(I) oxides as reusable catalyst in consecutive decarboxylative
C-H arylation and carbonylation: rapid synthesis of carbonyl dibenzofurans
a,‡
a,‡
b,‡
b
a,∗
Rammyani Pal , Nivedita Chatterjee , Manas Roy , Sabyasachi Sarkar , Swarbhanu Sarkar and
a,∗
Asish Kumar Sen
a
Organic and Medicinal Chemistry Division, CSIR-Indian Institute of Chemical Biology, 4, Raja S. C. Mullick Road, Kolkata-700 032, India
b
Department of Chemistry, Indian Institute of Engineering Science and Technology, Shibpur, Howrah 711 103, India
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Consecutive chemo- and regio-selective decarboxylative C-H arylation, followed by
carbonylative C-C coupling of aryl halide with isocyanide/alcohol was applied for the first
time in one-step synthesis of carbonyl dibenzofurans with nanodomain cuprous oxide under
aerobic condition. As a proof of concept, several novel dibenzofurans were synthesized from
2-(3-iodophenoxy) benzoic acid in good yield. The tandem protocol eliminates the use of
excess catalysts, hazardous organic solvents, heavy metals like palladium or rhodium, ligands,
oxidants or external additives. More importantly, the cubic Cu(I) nanocatalyst can be recovered
and recycled for three consecutive reactions without any significant loss of catalytic activity or
any change in its morphology. Use of water as solvent and reusable catalyst makes the reaction
environment friendly.
Available online
Keywords:
Tandem reaction
C-H activation
Carbonylation
C-C coupling
Cuprous oxide nanoparticle
2
009 Elsevier Ltd. All rights reserved.
Transition metal catalyzed intramolecular C-C and C-N
bond forming reactions via oxidative coupling of C-H bond
and heteroatom functionality have emerged as a promising
(I) oxide could be more promising compared to the
corresponding bulk materials or expensive palladium systems
due to its high reactivity, stability in aqueous medium,
environmental compatibility, non-toxicity and more
importantly its reusability. In addition, the regeneration of the
catalyst by simple centrifugation makes the work up processes
simpler.
1
method for the synthesis of structurally diverse heterocycles.
In this regard, domino reactions, in which multiple chemical
bonds can be constructed in one-pot, have evolved as highly
atom-economic alternative to the classical coupling approaches
2
using pre-functionalized substrates. Incorporation of C-H
Dibenzofurans exist in a wide variety of biologically active
functionalization into a domino reaction may be arguably ideal
and is no doubt very challenging. Compared to Pd-catalyzed
6
compounds. Methodologies leading to the edifice of this
3
skeleton are primarily based on Pd- and/or Cu-catalyzed
intramolecular O-arylation of 2-chlorobiphenyl alcohols,
tandem decarboxylation/C-C coupling of 2-phenoxybenzoic
acids (Scheme 1a), and consecutive C-H activation/C-O bond
formation of 2-arylphenols or oxidative C-C cyclization of
domino reactions involving C-H activation, comparable
4
approaches involving Cu-salts are underdeveloped. Apart
from atom economy and bond-forming efficiency, the
prevalence of consecutive reactions may lead to structurally
diverse scaffolds particularly important for medicinal
chemistry research.
7
diphenylethers. Strategy involving tandem decarboxylation/C-
C coupling of ortho-aryloxybenzoic acids for the synthesis of
5
Although very few references are available for the use of
dibenzofurans requires usage of higher amount of Ag-salts as
8
copper(I) oxide nanoparticles in organic synthesis including
various C-C cross coupling reactions, the feasibility of using
nanocatalyst in complicated reactions like domino
decarboxylative C-H arylations and carbonylative C-C
coupling still remains unexplored. Application of nano-copper
oxidants or excess metals. Shen et al. reported palladium-
catalyzed decarboxylative cyclization involving 2-(2-
bromophenoxy)benzoic acid where halides were used as
second reaction site and as leaving functionality (Scheme 1b)
using N-methyl-2-pyrrolidone (NMP, 0.2 M) as solvent. We
—
——
∗
Corresponding authors. Tel.: +91-33-2499-5806; fax: +91-33-2473-5197; e-mail: aksen@iicb.res.in; swarbhanu_2005@yahoo.co.in
‡
These authors contributed equally to this work

2
used 2-(3-iodophenoxy)benzoic acid which made both C-H
and C-I available for decarboxylative cyclization (Scheme 1c).
With this compound, competitive reaction like intermolecular
decarboxylative C-C coupling at iodide site is theoretically
aqueous environment, whereas, for the ester, ‘green organic
10
solvent’,
heptane was used. Ultrasonication provided
enhancement of the reaction rate compared to the conventional
procedures by dispersing insoluble ingredients in the medium.
8
possible. Also, transition metal (like palladium) catalyzed
carbonylation of aromatic halides with various nucleophiles,
9
2 8
We applied isocyanide or Co (CO) as the carbonyl source in
often leads to amides or esters. We, therefore, checked the
our domino strategy. Consecutive chemo- and regio-selective
decarboxylative C-H arylation, and carbonylative C-C
coupling of aryl halides lead to carbonyldibenzofurans only.
Here, intramolecular C-C coupling through C-H arylation was
found to be more favored in comparison to the decarboxylative
C-iodo arylation or intermolecular decarboxylative C-C
coupling at iodide site. C-iodo bond underwent C-C coupling
with organic isocyanides or alkoxycarbonylation with various
alcohols in chemoselective manner. For carbonylation of the
aryl halides, no externally added CO gas was required. Use of
CO at high pressure is, however, never recommended for
practical applications. Nano sized cubic cuprous oxide was
used as reusable catalyst under aerobic condition. No
additional oxidants or organic solvents were needed. Also,
application of air as oxidant and recyclable catalyst is
attractive from economic and environmental concerns. It is
worth mentioning that, previously known methods generally
required the involvement of intricate combination of ligands,
heavy metal catalyst, and organic solvents as reaction media
with various additives.
feasibility of the one-pot synthesis of carbonyldibenzofuran in
presence of nano sized cuprous oxide (Scheme 1c) under
sonication. Synthesis of amidodibenzofurans was executed in
a) Palladium catalyzed decarboxylative C-H arylation
CO H H
2
Pd(TFA)2
O
AgCO3
O
DMSO/dioxane
b) Palladium catalyzed decarboxylative C-Br arylation
CO HBr
2
Pd(OAc)2
PPh , K CO
3
3
2
O
NMP
O
X
c) This work: Resuasble nano copper(I) mediated regioselective
decaboxylative C-H arylation, C-I carbonylation
We synthesized cuprous oxide nanoparticles by reduction of
cupric chloride dihydrate using fructose as reducing and
capping agent in water. The cubic Cu(I) nanoparticles had an
average edge length of 180 ± 20 nm and were fully
R
CO H
O
-1
2
Cu(I) nanoparticle
Base
characterized using TEM, XRD, IR etc. Peaks at 627 cm in
FT-IR (Figure S1) can be assigned as Cu(I)–O stretching
O
R-NC, H O
-1
2
frequency and the absence of any peak around 512 cm
H
H
I
or
O
ensures nonexistence of traces of Cu(II)–O as contaminant in
R-OH, Co (CO)
11
2
8
the synthesized particles. The shape of the particles was
Heptane
X = NH, O
established by Scanning and Transmission Electron
Microscopy. The powdered X-ray Diffraction (XRD) pattern
Scheme 1. Tandem decarboxylation/C-C coupling for the synthesis of
(
(
3
Figure 1A) indicates the typical reflection patterns of cuprite
JCPDS no. 77-0199). 2θ values in the XRD plot at 29.4 º,
6.37º, 42.29º, 61.40 º, 73.64 º and 77.46 º were ascribed as the
dibenzofurans from 2-aryloxybenzoic acids.
12
crystal plane of 110, 111, 200, 220, 311 and 222 respectively.
d spacing values of the planes were calculated as 3.14, 2.59,
2
.29, 1.75, 1.61, 1.58 Å respectively. The SEM and TEM
images (Figure 1B and 1C) fully confirmed the regular cubic
shape of the synthesized nanoparticles.
Figure 1. A) Powder XRD pattern; B) SEM and C) TEM image of cuprous
oxide nanoparticles before reaction; D) TEM image of cuprous oxide
nanoparticles after 3 times use.

3
1
1
1
1
3
4
5
6
Cu
Nano-Cu
Nano-Cu
Nano-Cu
2
O
Cs
2
CO
3
AgCO
3
/ Piv
2
O
0
76
i
Before proceeding to the one-pot sequence, attempt was
made to customize the reaction parameters for the
decarboxylated C-H arylation (Scheme 2) in aqueous medium.
Initially we chose both compounds 1 and 3 for this purpose.
2
O
O
O
Pr
Et
CO
2
EtN
-
2
3
N
-
-
-
73
2
K
2
3
80
2
O
c
c
c
i
Multiple
spots
i
17
Nano-Cu
2
O
O
O
Pr
2
EtN
d
-
-
Multiple
spots
1
8
Nano-Cu
2
Et
3
N
d
Multiple
spots
19
Nano-Cu
2
K
2
CO
3
d
a
Reactions were performed in water (10 mL) using 1 (1 equiv.),
nano-Cu O (20 mol %), base (5 equiv.) under sonication (80 °C)
2
for 2 h and aerobic condition.
external additives (Table 1, entry 14-16). These reactions were
completed within 2 h. The effect of different bases was also
explored successively. We found both organic and inorganic
bases gave comparable yield when employed in 5.0 mole
equivalent.
b
Recovered yield.
Reaction performed with compound 3 using similar experimental
c
conditions.
d
No product could not be isolated in pure form.
On the contrary, compound 3 when subjected to the above
reactions, produced a complex array of products (without any
major spot) as visualized by TLC (Table 1, entry 17-19). It was
not possible to separate them by column chromatography (data
not included). This happened because of the involvement of
iodide in various intermolecular coupling such as, self
coupling and in conjunction with single or double C-H
activation. Therefore, the data obtained using compound 1 was
subsequently used for designing the one-pot reaction in
aqueous medium.
R
X
CO H
Cu2O nanoparticle
Sonication, 80 C
2
O
o
O
H
Base
O
I
X = NH, O
For X = NH; Alkyl/aryl isocyanide
For X = O; Ar-OH and Co (CO)
3
CO H
4
2
2
8
Cu O nanoparticle
Sonication, 80 C
2
o
O
H
O
H O, Base
2
Scheme 3. Decarboxylative C-H arylation-carbonylative C-C
functionalization in tandem.
2
1
Scheme 2. Decarboxylative C-H arylation.
p-fluoro-isocyanide produced desired amido-dibenzofurans,
4
a, 4b, 4c and 4d in 59, 57, 52 and 48 % respectively. Use of
aliphatic isocyanides did not affect the yield of the product.
The cyclopropyl amido derivative 4f and 4g were formed
respectively in 46% and 49% yield when cyclopropyl
isocyanide was used as carbon source. Activated aliphatic
isocyanide like benzyl isocyanide also reacted under similar
condition to provide 4e in 52% yield. For the synthesis of
Next the methodology was applied in the tandem sequence
Scheme 3). 2-(3-Iodophenoxy)benzoic acid (3) was used for
this study and the results are shown in Figure 2. Aryl
isocyanides, e.g., phenyl isocyanide, p-toluidine isocyanide, p-
methoxy and
(
2 8
ester, similar protocol was applied with Co (CO) . Baburajan
1
3
et al. used the same cobalt-complex as CO source for the Pd-
catalyzed alkoxycarbonylation of aryl halides. However, the
scope of the reaction was not investigated using copper salts.
Using copper nano-catalyst and various aromatic alcohols,
desired dibenzofuran derivatives (4h-4m) were obtained in
good yield using our one-pot cascade strategy. α-Naphthol
gave the maximum yield (4h) of 61%. The presence of bulky
phenyl at the ortho-position did not affect the tandem reaction,
and 57% of 4i was obtained when [1,1'-biphenyl]-2-ol was
used as alcohol source. However, the presence of strong
electron withdrawing group at p-position decreased the yield of
the corresponding ester 4j (47%). Halogens such as chloride
were also found to be compatible with the process to afford the
corresponding dibenzofurans 4k in good yield. Substrates
having an activated hydroxyl like benzyl alcohol reacted
smoothly to afford 4l in 55%. It is worth to mention that
similar reaction can be carried out with bulk copper salt
Table 1. Optimization of reaction conditions.
a
b
Entry
Catalyst
Base
Additives
Yield (%)
i
1
2
3
4
5
6
7
8
9
CuI
Pr
2
EtN
-
0
0
0
0
0
0
0
0
0
0
0
0
CuI
-
AgCO
AgCO
Piv
AgCO / Piv
AgCO / Piv
AgCO / Piv
AgCO / Piv
AgCO / Piv
AgCO / Piv
AgCO / Piv
3
i
i
i
CuI
Pr
Pr
Pr
2
2
2
EtN
EtN
EtN
3
CuI
2
O
CuI
3
2
O
O
O
O
O
O
O
O
CuI
-
-
3
2
Cu
Cu
[(IPr)
2
O
O
3
2
i
i
2
Pr
Pr
2
EtN
EtN
3
2
2
Cu]PF
6
2
3
2
1
1
1
0
1
2
Cu
2
O
O
O
DBU
Et
3
2
(
2
Cu O/CuI) in polar organic solvents like DMF. Compound 4b
Cu
2
3
N
3
2
was formed in comparable yield (60%, data not shown) from
compound 3 under similar reaction conditions. However, the
Cu
2
K
2
CO
3
3 2
AgCO / Piv

4
purpose of the present study is to develop novel green reaction
methodology with water as solvent.
FTIR and powder XRD pattern of the nanoparticle and are
depicted in Figure S1 and Figure S2 respectively
(
supplementary information).
Having shown that the reaction proceeds with generality,
the possible mechanism of the reaction was explored (Figure
In conclusion, we have demonstrated that the nano copper
3
). It is expected that initially oxidative addition of Cu(I) into I
(I) oxide catalyzed decarboxylative intramolecular C-H
arylation and carbonylative C-C coupling of 2-(3-
iodophenoxy)benzoic acid with isocyanide/alcohol can
forms intermediate II, which is then readily converted into
intermediate III due to the liberation of iodide and the
formation of Cu(III)-O bond in the presence of base. The
chemoselectivity may be attributed from the formation of the
cyclic intermediate III, where the Cu(III) is coordinated with
both the aryl ring and the oxygen of the carboxylic acid
simultaneously and thus preventing intermolecular C-C
coupling at the iodide site.
1
4
generate a library of dibenzofuran derivatives. The reaction
parameters allow the reaction to take place with high chemo-
and regio-selectivity. Use of 2-(3- iodophenoxy)benzoic acid
made both C-H and C-I available for intra- as well as inter-
molecular C-C cross-coupling. The intramolecular C-C
coupling through C-H arylation was found to be more favoured
in comparison to decarboxylative C-iodo arylation at the iodide
site. C-iodo bond underwent chemoselective C-C coupling
with organic isocyanides or underwent alkoxycarbonylation
with various
H
H
H
N
N
N
O
O
CH3
O
OCH3
O
O
O
4a (59 %)
4b (57 %)
4c (52 %)
MeO
H
N
H
H
N
H
N
N
O
O
O
O
O
O
F
O
O
4d (48 %)
4e (52 %)
4f (46 %)
4g (49 %)
Ph
O
O
O
O
NO2
O
O
O
O
O
4j (47 %)
4
i (57 %)
4
h (61 %)
H3C
O
Ph
O
O
O
O
O
O
O
O
Cl
4
k (60 %)
4l (55 %)
4m (52 %)
Figure 2. Synthesized dibenzofurans via decarboxylative C-H arylation
and carbonylative C-C functionalization.
Cu(III) in the cyclic intermediate III, may easily form
coordinate bond with the π-electrons of linear isocyanide and
migratory insertion of isocyanide happens to generate
intermediate IV. Decarboxylation of IV may lead to the
Figure 3. Plausible catalytic cycle for the formation of substituted
dibenzofuran.
2
formation of intermediate V. In the presence of H O, this
unstable intermediate V isomerized to amide VI. The
arylcopper intermediate VI thus formed readily participates in
intramolecular C-H activation to yield the intermediate VII,
from which C-C bond forming reductive elimination affords
the substituted dibenzofuran product VIII with the
regeneration of Cu(I) to be used for the next cycle.
The reusability of the nano particles (NPs) towards the
synthesis of dibenzofuran derivative 4a was investigated next
and the results are appended in Figure 4. The nano-catalyst
was recovered (~95%) by centrifugation after each reaction
and was washed with ethanol repeatedly to avoid any
contamination. It is evident that, the catalytic activity did not
affect much up to three consecutive cycles, however,
significant loss in the catalytic property was noticed
afterwards. The unchanged morphology of the nanocatalyst
Figure 4. Reusability of the nano-catalyst towards the synthesis of 4a.
alcohols in chemoselective manner. The protocol did not
require use of heavy metals like palladium or rhodium,
hazardous organic solvents, ligands, oxidants or external
additives. More importantly, the cubic nanocatalyst can be
recovered and recycled for three consecutive reactions without
any significant loss of reactivity or any change in its
morphology. Reaction methodology provides considerable
functional group tolerance which may provide synthetic
flexibility for further functional group interconversion. Further
rd
was confirmed by TEM-analysis (Figure 1D) up to 3
recycles. The oxidation state and unchanged morphology of
the nanoparticles (after reaction) was further confirmed by

5
applications of this strategy in organic synthesis are currently
under investigation in our laboratory.
2 3
mol%) and K CO (5.0 equiv.) were added and stirred vigorously
under sonication for 2 h at 80 °C. After that, ethyl acetate (50 mL) was
added into the reaction mixture and thoroughly vortexed. It was then
centrifuged to separate the nanoparticles, aqueous and ethyl acetate
layers and were collected separately. The aqueous layer was re-
extracted with ethyl acetate once. The combined ethyl acetate layer
containing the product was concentrated and purified by column
chromatography (Hexane/EtOAc) to give pure products (4a-g). The
nanoparticles were washed with EtOAc-ethanol (1:1 x 3) and dried
under vacuum before re-use. For the synthesis of dibenzofuran-1-
carboxylate similar procedure was followed but the reaction was
executed in commercial heptane with Co (CO) (0.5 equiv.) and
Acknowledgements
The authors express their gratitude to the Director, CSIR-
IICB for laboratory facilities. We are also thankful to Dr. T.
Sarkar and Mr. K. K. Sarkar for recording NMR and ESI-MS
respectively. R.P. and N.C. thank CSIR, New Delhi for
providing Senior Research Fellowship (SRF). M.R. gratefully
acknowledges DST- SERB for proving him fellowship in DST
Fast Track Start-Up Research Grant Scheme. The SERB, DST,
New Delhi is thanked for providing a Raja Ramanna
Fellowship to S.S. at IIEST, Shibpur.
2
8
2
Cu O-NPs (40 mol%) under non-aerobic condition.
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4. General procedure for the synthesis of benzofuran-1-carboxamide
4a-g) and dibenzofuran-1-carboxylate (4h-m): In an open round-
bottomed flask containing water (25 mL), 2-(3-iodophenoxy)benzoic
acid (1, 1.0 equiv.) and isocyanide (2, 1.2 equiv.), Cu O-NPs (20
1
(
2

6
Graphical Abstract:
Cubic nano-copper(I) oxides as reusable
catalyst in consecutive decarboxylative
C-H arylation and carbonylation: rapid
synthesis of carbonyl dibenzofurans
Rammyani Pal, Nivedita Chatterjee, Manas
Roy, Sabyasachi Sarkar, Swarbhanu Sarkar
and Asish Kumar Sen

7
Highlights
1
2
3
4
5
. The unique one-step synthesis of carbonyl
dibenzofurans was developed
. It involves decarboxylative C-H arylation and
carbonylative C-C coupling
. The reaction is highly chemo- and regio-
selective and environ friendly
. Reusable nanodomain cuprous oxide was used
as catalyst under aerobic condition
. Several derivatives were synthesized which
showed high functional group tolerance
1
5.