Direct CuO nanoparticle-catalyzed synthesis of poly-substituted furans: Via oxidative C-H/C-H functionalization in aqueous medium

Article abstract of DOI:10.1039/c6ra04181g

Here, we have reported synthesis of 3,4-dicarbonyl substituted poly-functionalized furan derivatives via direct functionalization of α,β-unsaturated carbonyl compounds through conjugate addition initiated domino reactions using CuO nanoparticles as a reusable catalyst in aqueous ethanol.

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Direct CuO nanoparticles catalyzed synthesis of poly-substituted
furans via oxidative C-H/C-H functionalization in aqueous medium
Soumen Payra,a Arijit Saha,a Sandip Guchhaitb and Subhash Banerjeea,*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Here, we have reported synthesis of 3,4-dicarbonyl substituted
Historically, furans can be synthesized via acid catalyzed
poly-functionalized furan derivatives via direct functionalization of Paal−Knorr method via intramolecular cyclization of 1,4-
α,β-unsaturated carbonyl compounds through conjugate addition dicarbonyls3 and intermolecular Feist−Benary4 methods. Many
initiated domino reactions using CuO nanoparticles as reusable of the protocols have used acyclic ketone precursors as
catalyst in aqueous ethanol.
starting materials and produced furan derivatives via alkyne-
or allene-assisted cyclizations.5 In the past few decades,
synthesis of furan derivatives via transition-metal catalyzed
inter/intramolecular condensation have also been carried out
extensively.6 However, in the context of green chemistry,
intermolecular approaches were favored due to the
straightforward formation of diverse furan scaffolds from
simple building blocks. However, surprisingly the synthesis of
dicarbonyl substituted furans has rarely been reported in the
literature.7 Zhuo et al.7d have reported for the first time, MnO2
mediated ZnCl2 assisted synthesis of 3,4-dicarbonyl furan
derivatives in acetic acid medium. However, the Zhuo’s
method was associated with several limitations such as use of
excess amount of ZnCl2/MnO2 as catalyst (6 equivalents) which
are not reusable, harsh reaction conditions (refluxing in acetic
Direct synthesis of polysubstituted furans has attracted
considerable attention as these moieties represent the most
versatile and important class of five-member heterocyclic
compounds and constitute as core entities in many natural
products and biologically active drug molecules1 (Figure 1).
These moieties have also found various biological,
agrochemicals, and pharmaceutical applications. In addition,
furans are important in organic synthesis as targets and
building blocks.2 In view of the great importance of furans, the
development of clean and straightforward synthetic methods
from simple and inexpensive reagents is highly desirable.
O
o
O
MeO2C
acid at 130 C), longer reaction time (24 h) and lower isolated
Cl
O
OH
CO2H
yields of products (15-80 %). Thus, development of an efficient
and greener protocol for the synthesis of 3,4-dicorbonyl furan
derivatives is highly appreciated.
O
O
O
Me
RO
Selective inhibitor
of MetAP
Angelone
R=H, Tournefolin C
R=Me, Tournefolin B
The introduction of nanoparticles (NPs) could be an attractive
to overcome the above mentioned limitations due to their
unique properties of larger and highly reactive surface areas.8-9
Very recently, metal oxide NPs have been widely applied as
catalyst because of their dual Lewis acid and Lewis base nature
and redox properties on the surface.10 copper oxide (CuO) NPs
catalyzed carbon–carbon and carbon-hetero atom bond
formations have evolved as useful methods for the synthesis
Me
CHO
O
O
N
HN
N
HO
HO
OH
OH
O2N
N
O
O
N
CO2H
N
O
O
H
NCGC00189258-01
Dimethylfuroguaiacin
Dantrolene
Fig. 1 Some furan derived natural products and drugs.
of novel heterocyclic compounds.11-14 As
a part of our
a.Department of Chemistry, Guru Ghasidas Vishwavidyalaya (A Central University),
Bilaspur – 495009 (Chhattisgarh), India
continuous effort in exploring catalytic activity of metal oxide
NPs in organic transformation,15 here, we have demonstrated
CuO NPs catalyzed synthesis of polysubstituted 3,4-dicarbonyl
furan derivatives via oxidative C-H/C-H functionalization
reaction between α,β-unsaturated ketones and 1,3-dicarbonyl
compounds or β-keto esters in water-ethanol. Here, tertiary
butyl hydroperoxide (TBHP) is used as oxidant (Scheme 1).
b.Department of Organic Chemistry, Indian Association for the Cultivation of
Science, Jadavpur, Kolkata 700032, India
†
*Corresponding author; email: ocsb2009@yahoo.com.
Electronic Supplementary Information (ESI) available: Detailed experimental
procedure, spectral data, copies of 1H, 13C NMR, HRMS and FT-IR spectra, powder
XRD of recycled CuO NPs etc. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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The powder XRD pattern indicates the formation of single
phase monoclinic CuO NPs with reflection planes at (110), (-
111), (111/200), (-202), (020), (202), (-113), (022/-311),
(113/220), (311), (004/-222) (card JCPDS 72-0629).16 The
average particle size of CuO NPs was determined to be 10 nm,
calculated from full width at half maxima (FWHM) at reflection
Scheme 1 Synthesis of 3,4-dicarbonyl functionalized furan (111/200) plane using Debye Scherrer formula. The formation
derivatives.
of spherical CuO NPs was indicated from TEM image (Figure
2b).
Using well characterized CuO NPs, next we have attempted
to synthesize less explored 3,4-dicabonyl substituted furan
derivative via oxidative reaction of 1,3-diphenyl-prop-2-ene-
1one (1a) and acetylacetone (2b) in ethanol. When a mixture
of 1a (1 mmol), 2b (5 mmol) was refluxed in presence of CuO
NPs (10 mg), 40% of the desired furan derivative (3a) was
obtained after 12h (entry 1, Table1) without any oxidizing
agent. The addition of tertiary butyl hydroperoxide (TBHP) as
oxidizing agent (1 equivalent) significantly improves the yield
and shortens the reaction time (3 h) (entry 7, Table 1).
Results and Discussion
Initially, we have synthesized CuO NPs following previously
reported protocol.16 Briefly, aqueous solution of Cu(NO3)2 was
condensed under basic conditions (pH was adjusted to 11 by
addition appropriate amount of NaOH solution) and stirred for
o
2 h at 70 C. The black precipitate appeared which was cooled
to room temperature, washed thoroughly with water and
ethanol, calcinated at 400 oC for 3 h and analyzed by analytical
techniques. The formation of CuO NPs was confirmed by the
powder X-ray diffraction (XRD) and transmission electron
microscopic (TEM) study (Figure 2a and 2b).
Table 1 Optimization of reaction conditions
Entry catalyst
solvent
oxidant Time Yielda
(h)
12
(%)
40
17
-
26
49
44
72
85
1
2
3
4
5
6
7
8
CuO NPs
CuFe2O4
Cu(OAc)2
ZnO NPs
CuO NPs
CuO NPs
CuO NPs
CuO NPs
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH-
H2O(1:1)
DMSO
DMF
EtOH-
H2O(1:1)
-
-
-
-
12
12
12
12
12
3
K2S2O8
DDQ
TBHP
TBHP
3
9
10
11
CuO NPs
CuO NPs
CuO NPs
TBHP
TBHP
TBHP
3
3
3
42
33
86b
Reaction conditions: α,β-Unsaturated ketone (0.5 mmol),
1,3 Dicarbonyl compound (2.5 mmol), Catalyst (10 mg),
a
Oxidant (1 equiv.), solvent (2.0 mL), reflux, air. Yields refer
to the isolated products. bCatalyst (15 mg).
The TBHP works better than K2S2O8 and DDQ as oxidizing agent
(entries 5-6, Table 1). CuO NPs showed superior to other
catalysts like CuFe2O4, Cu(OAc)2, ZnO NPs tested here (entries
2-4, Table 1). Water-ethanol mixture (1:1) was proved to be
the best solvent (entry 8, Table 1) over DMF, DMSO etc as
solvent (entries 9-10, Table 1). The yield of the product did not
increase significantly by increasing the amount of CuO NPs
(entry 11, table 1). Thus, a combination of 1,3-diphenyl-prop-
2-ene-1one (1a), acetylacetone (2b) and TBHP (1:5:1 molar
ratio) in the presence of CuO NPs (10 mg) under refluxing in
Fig. 2 (a) Powder x-ray diffraction pattern of CuO NPs; (b)
transmission electron microscopic image of CuO NPs.
2 | J. Name., 2012, 00, 1-3
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water-ethanol (1:1) for 3 h is considered as optimum reaction After successful application of the CuO NPs in synthesizing 3,4-
conditions (entry 8, Table 1). dicarbonyl furans, we have tried to extend the scope of this
Using optimized reaction conditions and following a simple reaction by replacing 1,3-dicarbonyl compounds with β-keto
experimental procedure,17a next, we have explored the scope esters as substrate under the standard reaction conditions.
of this method. It is evident from Table 2 that a number of α,β When a mixture of 1,3-diphenyl-prop-2-ene-1one (1a), ethyl
unsaturated carbonyl compounds and 1,3-dicarbonyl acetoacetate (4a) and TBHP (1:5:1 molar ratio) was heated at
o
compounds were participated in this C-H/C-H oxidative 80 C in water-ethanol (1:1) in presence of CuO NPs (10 mg),
reaction leading to 3,4-dicarboylsubstiuited furan derivatives good yield of diverse furan derivative (5a) was obtained within
in good to excellent yields (75-91%) within 3 h. The reaction practical time period (2 h). In a simple experimental
conditions are mild enough to tolerate various functional procedure,17b we observed that different α,β-unsaturated
groups such as -Cl, -Br,-NO2, -OMe (3a−3l) etc. present in ketones and β-keto esters were participated smoothly in the
substrate. It was noteworthy that electronic effect had little above methodology under standard conditions. Furthermore,
influence on this oxidative coupling. To our delight, we observed that under the similar reaction conditions the
benzylidene acetone worked well with acetylacetone, and reaction took place in the presence of benzylidene acetone
produced the desired product (3l) in good yield. Moreover, (5f).
both open chain and cyclic 1,3-dicarbonyl compounds were
participated in this reaction without any problem.
Table 3 Substrate scope for the synthesis of 3,4-dicarbonyl
Table 2 Substrate scope for the synthesis of 3,4-dicarbonyl furan derivatives from α,β-unsaturated ketones and β-keto
furan derivatives
esters
O
O
O
O
O
O
O
R1
R2
R3
R4
CuO NPs (10 mg)
EtOH:H2O (1:1)
TBHP (1 .0 equiv)
Reflux, 3.0 h
O
O
O
R1
R2
OR4
R3
+
CuO NPs (10 mg)
R1
R2
R3
R4
+
R1
R2
R3
OR4
EtOH:H2O (1:1)
TBHP (1 .0 equiv)
80oC, 3.0 h
O
O
2
1
3
4
1
5
O
O
O
O
O
O
O
O
O
O
O
O
OEt
OEt Br
OEt
O
O
O
O
O
O
Me
MeO
Br
MeO
3a, 85%
3b, 80%
3c, 81%
5a, 77%
5b, 83%
5c, 74%
O
O
O
O
O
O
O
O
O
O
O
O
O2N
OEt
OEt
OEt
O
O
O
O
O
O
Me
Cl
Br
Me
MeO
3d, 87%
3e, 91%
3f, 83%
5f, 70%
5d, 76%
5e, 73%
O
O
O
O
O
O
O
O
O
O
O
O
Br
Cl
Cl
OEt
OMe
OiPr
O
O
O
O
O
O
MeO
Cl
MeO
Cl
3g, 83%
3h, 89%
3i, 86%
5g, 87%
O
5h, 74%
5i, 77%
O
O
O
O
O
O
O
O
O
OEt
OEt
O
O
O
O
O
3j, 75%
3k, 81%
3l, 83%
5k, 81%
5j, 89%
Cl
O
O
Cl
O
O
aReaction conditions: α,β-Unsaturated ketone(0.5 mmol), β-
keto esters (2.5mmol), CuO NPs (10 mg), TBHP (1 equiv) in
O
O
b
EtOH:H2O (1:1; 2.0 mL) at reflux for 3 h in open air. Yield of
3m, 88%
Cl
Cl
3n , 82%
the isolated product.
Reaction conditions: α,β-Unsaturated ketone (0.5 mmol), 1,3-
Dicarbonyl compound (2.5 mmol), CuO NPs (10 mg), TBHP (1
equiv) in EtOH:H2O (1:1; 2.0 mL) at reflux for 3 h under air.
bYields refer to those of pure isolated products.
All the reactions listed in table 2 and table 3 were clean and
afforded good to excellent yields (70-91%) of the products
within practical time period (1.5-3 h). The present method of
synthesizing the 3,4-dicarbonyl substituted furans offered
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several advantages over previously reported Zhuo’s method The reaction of 3-diphenyl-prop-2-ene-1one (1a) and acetyl
such as (i) better isolated yields of the products, (ii) shorter acetone (2b) in presence of CuO NPs was suppressed in
reaction time, (iii) use of catalytic amount of CuO NPs in place presence of 2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), a
of excess (6 equivalent) catalyst, MnO2/ZnCl2, (iv) milder radical quencher, which supports the formation of radical
reaction condition of heating at 80 oC in water-ethanol mixture intermediate.
Thus,
following
previously
reported
o
than previous heating at 130 C in acetic acid, and finally (v) mechanism7d and above control experiment, we have given a
greener alternative protocol. A comparison between the two plausible mechanism for synthesis of furan 3a (Scheme 2) in
methodologies has been presented in Table 4.
water-ethanol medium. The feasibility of radical reaction in
water was demonstrated by Liu et al.18
O
t-BuO
Table 4 Comparison of the previous and present method for
O
O
O
O
O
O
Ph
Ph
the synthesis of 3,4-dicarbonyl substituted furans
t-BuO
OH
t-BuOOH
Ph
Ph
t-BuOOH
= CuO NPs
O
Sl
Catalyst/Condit Time/Yield
Reusability Ref.
SET
O
[O]
O
OH
No. ions
1
2
MnO2/ZnCl2/
AcOH, 130 oC
24 h/15-83% No
7d
O
O
O
O
O
O
O
Ph
Ph
Ph
O
Ph
Ph
-H
H
O
Ph
t-BuOOH
[O]
CuO NPs (10 3 h/70-91%
mg)/H2O-EtOH,
80 oC
Yes
Present
work
Ph
O
O
O
O
Scheme
2 Plausible mechanism for CuO NPs catalyzed
synthesis of 3a.
Finally, we have investigated the reusability of the CuO NPs for
the synthesis 1-(4-benzoyl-5-(4-methoxyphenyl)-2-
methylfuran-3-yl)ethanone (3c, Table 2). After the reaction,
the CuO NPs was separated by centrifugation and washed
thoroughly with water (2x2 ml) and ethanol (2x1 ml), dried and
reused for subsequent reactions. The CuO NPs was reused up
to six times without significant loss of catalytic activity,
however, the after that yield of the product dropped to 65 %
(Fig 3). The decrease in yield could possibly due to the
aggregation of NPs during the course of the reactions or loss of
surface functional groups.15h The powder XRD pattern (Fig. S1,
ESI-7) of recycled CuO NPs after 4th run revels that the
monoclinic morphology of the particles was intact however,
the particles sizes increased (~ 15 nm, calculated from FWHM
using Sherrer formula).
Conclusions
In conclusion, we have demonstrated CuO NPs catalyzed
oxidative C-H/C-H functionalization of 1,3-dicarbonyls or β-
keto esters with α,β-unsaturated carbonyl compounds leading
to 3,4-dicarbonyl substituted poly-functionalized furan
derivatives in aqueous medium. The present protocol offered
several advantages such as (i) higher isolated yields (70-91 %),
(ii) faster reaction time (3 h), (iii) use of catalytic amount (10
mg for 1 mmol of 1,3-diketone) of CuO NPs, (iv) milder
reaction conditions, (v) use of aqueous ethanol as green
solvent and finally, (vi) recyclability of CuO NPs catalyst made
the protocol environment benign in nature.
Notes and references
80
70
60
50
40
30
20
10
0
‡Footnotes relating to the main text should appear here. These
might include comments relevant to but not central to the
matter under discussion, limited experimental and spectral data,
and crystallographic data.
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,
substituted furan derivative. Representative procedure for
the synthesis of 1-(4-Benzoyl-5-(4-methoxyphenyl)-2-
methylfuran-3-yl)ethanone (3c, Table 2): A mixture of(E)-3-
(4-methoxyphenyl)-1-phenylprop-2-en-1-one (0.5 mmol;
119.14 mg), acetyl acetone (2.5 mmol; 250 mg), TBHP (1
equiv.) and CuO nanoparticles (10 mg) was refluxed in
ethanol: water (1:1, 2 ml) for 3 hours. After completion of
the reaction (TLC monitored), the resulting mixture was
cooled to room temperature and centrifuged to separate the
catalyst. The organic layer was extracted with ethyl acetate
(25 mL), washed with brine solution (3 × 5 mL) and dried
over anhydrous sodium sulfate. Evaporation of solvent left
the crude solid product which was purified by column
chromatography on silica gel (ethyl acetate/petroleum ether
= 1/9) to provide pure 1-(4-benzoyl-5-(4-methoxyphenyl)-2-
methylfuran-3-yl)ethanone (135.4 mg, 81%, 3c; Table 2) as
pale yellow solid. The structure of the product was
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confirmed by spectroscopic (1H NMR and 13C NMR) studies
1
and elemental analysis. H NMR (500 MHz, CDCl3): δ 8.01 (d,
J = 7.5 Hz, 2H), 7.61-7.55 (m, 3H), 7.51 (t, J = 7.5 Hz, 2H), 6.93
(d, J = 8.5, 2H), 3.86 (s, 3H), 2.55 (s, 3H), 2.16 (s, 3H), Anal
calc for C21H18O4: C, 75.43; H, 5.43 %; Found: C, 75.40; H,
5.45 %. These results are in good agreement with those of
reported one.7
The similar method was followed for all the furan
derivatives listed in Table 2 and Table 3 except in case of
table 3 β-keto esters was used in place of 1,3-diketones.
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DOI: 10.1039/C6RA04181G
Graphical Abstract
Direct CuO nanoparticles catalyzed synthesis of poly-substituted furans via oxidative C-H/C-H
functionalization in aqueous medium
Here, we have reported synthesis of 3,4-dicarbonyl substituted poly-functionalized furan derivatives via direct functionalization of α,β-
unsaturated carbonyl compounds through conjugate addition initiated domino reactions using CuO nanoparticles as reusable catalyst in
aqueous ethanol.