α-Arylation of β-diketones with aryl halides catalyzed by CuO/aluminosilicate

Article abstract of DOI:10.1016/j.tetlet.2014.10.098

α-Arylation of β-diketones has been carried out over CuO/aluminosilicate catalyst under ligand-free condition. The reaction conditions were optimized with different solvents, bases, catalyst amounts, and temperatures using acetylacetone and 4-bromobenzaldehyde as a model system. The scope of the catalytic system was extended to include various substituted aryl halides. 27 examples were successfully demonstrated and the yields were ranging from 55% to 94%. C-Br bond was regioselectively activated in the presence of C-Cl bond. Similarly acetylacetone was chemoselectively arylated by 4-bromobenzaldehyde in the presence of dibenzoylacetone. Heterogeneous nature of the catalyst was confirmed by hot-filtration test. The catalyst was also found to be reusable.

Full text of DOI:10.1016/j.tetlet.2014.10.098

Accepted Manuscript
α-Arylation of β-diketones with aryl halides catalyzed by CuO/aluminosilicate
S. Ganesh Babu, R. Sakthivel, N. Dharmaraj, R. Karvembu
PII:
S0040-4039(14)01792-4
DOI:
http://dx.doi.org/10.1016/j.tetlet.2014.10.098
TETL 45327
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
18 August 2014
14 October 2014
15 October 2014
Please cite this article as: Ganesh Babu, S., Sakthivel, R., Dharmaraj, N., Karvembu, R., α-Arylation of β-diketones
with aryl halides catalyzed by CuO/aluminosilicate, Tetrahedron Letters (2014), doi: http://dx.doi.org/10.1016/
j.tetlet.2014.10.098
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Graphical Abstract
α-Arylation of β-diketones with aryl halides
Leave this area blank for abstract info.
catalyzed by CuO/aluminosilicate
S. Ganesh Babu, R. Sakthivel, N. Dharmaraj, R. Karvembu

1
Tetrahedron Letters
journal homepage: www.elsevier.com
-Arylation of -diketones with aryl halides catalyzed by CuO/aluminosilicate
S. Ganesh Babua,b, R. Sakthivela, N. Dharmarajc, R. Karvembua,*
a
Department of Chemistry, National Institute of Technology, Tiruchirappalli – 620015, India
SRM Research Institute, SRM University, Kattankulathur – 603203, Chennai, India
b
c Department of Chemistry, Bharathiar University, Coimbatore – 641046, India
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
-Arylation of -diketones has been carried out over CuO/aluminosilicate catalysts under
ligand-free condition. The reaction conditions were optimized with different solvents, bases,
catalyst amount and temperature using acetylacetone and 4-bromobenzaldehyde as a model
system. The scope of the catalytic system was extended to include various substituted aryl
halides. 27 examples were successfully demonstrated and the yields were ranging from 55 to
94%. C‒Br bond was regioselectivly activated in the presence of C‒Cl bond. Similarly
acetylacetone was chemoselectivly arylated by 4-bromobenzaldehyde in the presence of
dibenzoylacetone. Heterogeneous nature of the catalyst was confirmed by hot-filteration test.
The catalyst was also found to be reusable.
Available online
Keywords:
CC coupling
CuO/aluminosilicate
-diketones
© 2014 Elsevier Ltd. All rights reserved.
Aryl halides
Reusable
Ullmann type reaction was reported and the effect of particle size
of CuNPs on the self-coupling of aryl halide was studied.16
CC bond formation is one of the challenging and important
tasks in the field of synthetic chemistry.1,2 Heck, Negishi and
Suzuki were honored with the 2010 Nobel prize for their
contribution towards the development of Pd-catalyzed cross
coupling for CC bond formation. C–C couplings find much
attention because the final products can be used in
pharmaceutical and fine chemical industries.3-7 For instance,
SuzukiMiyaura reaction is a noble method to produce CC
bond via cross-coupling of aryl halide with arylboronic acid,
which is a key synthetic step in the production of agrochemicals,
polymers and pharmaceuticals. Cu based nanocatalysts are
cheaper and effective, which are being used in many C–C
coupling reactions.8 Thathagar et al., reported the Cu nanocluster
as a superior catalyst for the Suzuki cross-coupling.9 Calo et al.,
have used nano Cu as an inexpensive and eco-friendly catalyst
for the Heck reaction in ionic liquid.10 Ligand-free Cu2O-
catalyzed Mizoroki–Heck cross-coupling was achieved by Peng
et al., to produce CC bonds.11 Kantam et al., prepared
nanocrystalline CuO, tested its catalytic activity towards A3-
coupling to produce propargylamines and proposed a plausible
mechanism.12 CC bond formation is a vital step in the
Friedlander quinoline synthesis to obtain quinoline moiety and it
was economically carried out using reusable CuO nanoparticles.13
Kantam et al., have reported CuO nanoparticles-catalyzed
asymmetric aldol reaction with good yields and
enantioselectivities in the presence of (1S, 2S)-()-1, 2-
diphenylethylenediamine at -30 C to generate optically active -
hydroxy carbonyl compounds via CC coupling reaction.14
Higher activity was observed for Cu nanocluster catalyst towards
Sonogashira cross-coupling.15 Cu nanoparticles-catalyzed
Figure 1. Curcumin analogues (a) androgen receptor antagonists and
(b) zinc chelators.
Even though there are numerous literature available for
heterogeneous nano Cu-catalyzed C–C coupling reactions, only
limited reports deal with the -arylation of -diketones. But -
arylation of -diketones is an important transformation in
pharmaceutical and agrochemical industries. For example, some
of the pharmaceutically important α-arylated β-diketones are
shown in Figure 1. Moreover, acetylacetone-coumarin (an -
arylated -diketone) can be used to anchor robust TiO2 to
develop dye sensitized solar cell.17 Hence, He et al., tried to
develop a novel catalytic system for -arylation of -diketones,
but accidentally -aryl ketones were formed instead of -aryl
diketones (Scheme 1).18
Scheme 1. CuCl/pincer-catalyzed formation of -aryl ketones.

2
Tetrahedron Letters
Some homogeneous Cu salts with co-ligands can behave as
and the yield of -arylated product was noted against time.
Initially the yield was proportional to time and the reaction
attained saturation at 18 h. So the optimum time for this reaction
is 18 h (Table 1, entries 2, 17-20).
effective catalysts for the -arylation of -diketones. A Cu(II)
complex which formed in-situ from Cu(OAc)2H2O and 1,1'-
trimethylene-2,2'-biimidazole acts as a catalyst to produce -
arylated -diketones (Scheme 2).19
Table 1. Optimization of reaction conditionsa
Scheme 2. Cu(OAc)2·H2O with co-ligand as a catalyst for the -
arylation of -diketones.
Catalyst
amount (mg) (C)
Temp. Time Yield
Similarly CuI/L-proline catalytic system has been utilized for
Entry Solvent Base
(%)b
the -arylation of -diketones (Scheme 3).20-22
(h)
1
2
3
4
5
6
7
8
9
DMSO K3PO4
DMF K3PO4
DMAc K3PO4
Toluene K3PO4
20
20
20
20
20
20
20
100 18
100 18
100 18
100 18
100 18
100 18
100 18
100 18
100 18
100 18
100 18
100 18
91
94
54
14
DMF
DMF
DMF
DMF
DMF
No base
KOH
K2CO3
No reaction
47
88
2
Scheme 3. CuI/L-proline-catalyzed -arylation of -diketones.
Similar to L-proline, pivalic acid can also be used as a ligand
for CuI-catalyzed -arylation of -diketones in DMF at 130 C
(Scheme 4).23
(CH3)3COK 20
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
0
No reaction
10 DMF
11 DMF
12 DMF
13 DMF
14 DMF
15 DMF
16 DMF
17 DMF
18 DMF
19 DMF
10
30
40
20
20
20
20
20
20
20
20
64
65
46
8
37
49
89
59
80
95
96
27
50
80
18
18
18
Scheme 4. CuI/pivalic acid-catalyzed -arylation of -diketones
followed by O-arylation.
120 18
100
6
100 12
100 24
100 36
To overcome the drawbacks of homogeneous catalysts such as
instability and lack of recyclability, development of
heterogeneous catalytic system has been progressing. Kidwai et
al., successfully achieved -arylated -diketones using
heterogeneous CuO nanoparticles (Scheme 5).24 However, no
information was provided regarding the leaching of Cu catalyst.
20 DMF
a
Reaction conditions: acetylacetone (3 mmol), 4-bromobenzaldehyde (1
mmol), base (3 mmol) and CuO/aluminosilicate in 10 mL solvent.
b GC yield.
Scope of the present protocol has been extended with various
substituted aryl halides and the results are given in Table 2. The
yields of the products were ranging from 35 to 94% (Table 2,
entries 1-27). No previous literature is available for the formation
of 3-(4-formyl)phenylpentane-2,4-dione via CC coupling or α-
arylation of β-diketone method. The present CuO/aluminosilicate
catalyst gave excellent yield in this case (Table 2, entries 1 and
5). To the best of our knowledge, this is the first report for
producing -arylated -diketones using aryl chlorides. Though
CCl bond is difficult to cleave compared to CI and CBr
bonds, the present catalyst activated the CCl bond also and
hence the -arylation of -diketones can be carried out using aryl
chlorides. This was evident from entries 5, 7, 9, 12, 20, 22 and 23
provided in Table 2.
The electron withdrawing substituent in para position
accelerated the reaction. No catalytic system has been reported so
far with meta and ortho substituted aryl halides. But this catalytic
system works well with these substrates (Table 2, entries 3, 10,
11, 15 and 21). These factors clearly showed the importance of
the present catalytic system. -Arylation was not only restricted
to acetylacetone (Table 2, entries 1-18) but also extended with
dibenzoylmethane (Table 2, entries 19-27). Because of the steric
hindrance associated with dibenzoylmethane, it reacted slowly
with aryl halides as compared to acetylacetone. Heterocyclic aryl
halide viz 2-bromopyridine was also used, which yielded 89% of
the product with acetylacetone (Table 2, entry 18) and 81% with
dibenzoylmethane (Table 2, entry 25). Similarly, coupling of 3-
iodopyridine with acetylacetone gave a good yield of 75% (Table
2, entry 17). Excellent functional group tolerance was observed
in all the cases. The aryl halides bearing an electron donating
Scheme 5. CuO nanoparticles-catalyzed -arylation of -diketones.
Herein we report a cheap, air stable, ligand-free, efficient,
reusable and heterogeneous CuO/aluminosilicate25 catalytic
system for -arylation of -diketones.
In order to get effective results, the reaction conditions were
optimized by changing the reaction variables such as reaction
time, base, solvent, catalyst amount and temperature. For this
purpose, acetyl acetone (3 mmol) and 4-bromobenzaldehyde (1
mmol) were chosen as model substrates. The reaction has been
performed in different solvents like DMSO, DMF, DMAc and
toluene (Table 1, entries 1-4). In DMF, the coupled product was
formed in good yield (94%). No reaction occurred without the
addition of
a base (Table 1, entry 5). -Arylation of
acetylacetone was carried out with four different bases [K3PO4,
K2CO3, (CH3)3COK or KOH] and a maximum yield was obtained
with K3PO4 (Table 1, entries 2, 6-8). No reaction proceeded
without the addition of the catalyst (Table 1, entry 9). Coupling
reactions were examined with 10, 20, 30 and 40 mg of the
catalyst, and the yield was found to be better with 20 mg of the
catalyst (Table 1, entries 2, 10-12). Reactions were conducted at
27, 50, 80, 100 and 120 oC and the yield of the product was 8, 37,
49, 94 and 89%, respectively which indicated that 100 oC was the
optimum reaction temperature (Table 1, entries 2, 13-16). The
progress of the reaction was monitored by GC at regular intervals

3
substituent were also tested (Table 2, entries 6, 14, 26 and 27)
and found to be moderately reactive.
19
20
24
12
70
63
(2)
(2)
Table 2. CuO/aluminosilicate-catalyzed -arylation of -
diketonesa
21
22
30
18
71
70
(2)
(2)
Time
(h)
Yield
(%)b
Entry
126
Aryl halide
-Diketone
23
20
24
74
56
(2)
(2)
94 (89)c
91 (89)c
80
2434
18
12
24
18
24
16
15
(1)
227
2535
20
81
(1)
(1)
(1)
(1)
(1)
(1)
(2)
2636
2736
24
24
57
35
3
(2)
(2)
420
526
628
720
90 (82)c
84 (80)c
84 (79)c
66
a Reaction conditions: -diketone (3 mmol), aryl halide (1 mmol), K3PO4 (3
mmol) and CuO/aluminiosilicate (20 mg, 8.0 mol%) at 100 C in 10 mL
DMF.
b GC yield.
c Isolated yield.
The coupling of acetylacetone with 1-bromo-4-chlorobenzene
revealed the regioselectivity of CuO/aluminosilicate-catalyzed -
arylation of -diketones (Scheme 6). In this case, there were two
products possible. But only one product (due to cleavage of
CBr) was formed predominantly (92%) over the other (8%).
This can be explained by the fact that bromo is a better leaving
group than chloro. Thus, this method can be easily adopted for
the regioselective coupling of acetylacetone with bromo group in
the presence of chloro group.
829
929
16
15
83 (82)c
73
(1)
(1)
10
24
20
75
(1)
(1)
1130
90 (83)c
Scheme 6. Regioselective coupling of acetylacetone with 1-bromo-
4-chlorobenzene.
1231
1327
1427
18
24
18
91 (87)c
62
(1)
(1)
(1)
To study the chemoselectivity, acetylacetone (3 mmol),
dibenzoylmethane (3 mmol) and 4-bromobenzaldehyde (2 mmol)
were allowed to react over CuO/aluminosilicate catalyst (Scheme
7). Coupling of acetylacetone with 4-bromobenzaldehyde
occurred faster with the GC yield of 82% whereas the other
reaction (between dibenzoylmethane and 4-bromobenzaldehyde)
proceeded to form only 18% of the corresponding product. This
study clearly revealed that this method can be applied for the
chemoselective coupling of acetylacetone with aryl halide in the
presence of dibenzoylmethane.
69
1532
1633
18
18
48
79
(1)
(1)
1729
1831
15
18
75
(1)
(1)
Scheme 7. Chemoselectivity of CuO/aluminosilicate catalyst.
89 (86)c
In order to prove the heterogeneous nature of the catalyst
and the absence of Cu leaching during the course of the reaction,
heterogeneity test was performed with the reaction between

4
Tetrahedron Letters
acetylacetone and 4-bromobenzaldehyde. The catalyst was
good yield. Regioselectivity, chemoselectivity, heterogeneity and
reusability of the catalyst have been tested. The results were
found to be reasonable.
separated through centrifugation from the reaction mixture at
approximately 62% formation of the coupled product. The
reaction progress in the filtrate was monitored. No further
coupling was occurred even after extended reaction time,
indicating that no active Cu species leached from the support
during the reaction (Fig. 2).
Acknowledgments
We acknowledge DST, Ministry of Science and Technology
Government of India for financial support under the Nanomission
project (SR/NM/NS-27).
References and notes
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2003, 345, 979.
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Chem. Soc. 2011, 32, 3853.
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Tetrahedron Lett. 2008, 49, 1498.
15. Thathagar, M. B.; Beckers, J.; Rothenberg, G. Green Chem. 2004, 6,
215.
Figure 2. Heterogeneity test [Reaction conditions: acetylacetone (3
mmol), 4-bromobenzaldehyde (1 mmol), K3PO4 (3 mmol) and
CuO/aluminosilicate (20 mg, 8.0 mol%) at 100 C in 10 mL DMF
for 18 h].
After washing the recovered CuO/aluminosilicate catalyst in
diethyl ether, we could reuse it for the reaction between
acetylacetone and 4-bromobenzaldehyde. The reaction was
carried out four times under identical reaction conditions with the
recycling of CuO/aluminosilicate catalyst. The yield of product
was 93% at the 1st run. No significant decrease was observed in
the 2nd and 3rd runs as the yield of product was 92% and 90%
respectively. There was a decrease in the yield of the product
during 4th (72%) run. The yield, however was good and
indicating a good reusability of the catalyst (Fig. 3).
16. Samim, M.; Kaushik, N. K.; Maitra, A. Bull. Mater. Sci. 2007, 30,
535.
17. Xiao, D.; Martini, L. A.; Snoeberger, R. C.; Crabtree, R. H.; Batista,
V. S. J. Am. Chem. Soc. 2011, 133, 9014.
18. He, C.; Guo, S.; Huang, L.; Lei, A. J. Am. Chem. Soc. 2010, 132,
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19. Liu, J.; Zeng, R.; Zhou, C.; Zou, J.; Chin. J. Chem. 2011, 29, 309.
20. Ullah, I.; Sher, M.; Khera, R. A.; Ali, A.; Nawaz, M.; Shkoor, M.;
Iqbal, I.; Imran, M.; Villinger, A.; Fischer, C.; Langer, P.
Tetrahedron 2010, 66, 3824.
21. Ali, A.; Ullah, I.; Sher, M.; Villinger, A.; Langer, P. Tetrahedron
Lett. 2009, 50, 118.
22. Ruttinger, R.; Leutzow, J.; Wilsdorf, M.; Wilckens, K.; Czekelius, C.
Org. Lett. 2011, 13, 224.
23. Aljaar, N.; Malakar, C. C.; Conrad, J.; Strobel, S.; Schleid, T.;
Beifuss, U. J. Org. Chem. 2012, 77, 7793.
24. Kidwai, M.; Bhardwaj, S.; Poddar, R.; Beilstein J. Org. Chem. 2010,
6, 35.
25. Babu, S. G.; Neelakandeswari, N.; Dharmaraj, N.; Jackson, S. D.;
Karvembu, R. RSC Adv. 2013, 3, 7774.
26. Sazanovich, I. V.; Balakumar, A.; Muthukumaran, K.; Hindin, E.;
Kirmaier, C.; Diers, J. R.; Lindsey, J. S.; Bocian, D. F.; Holten, D.
Inorg. Chem. 2003, 42, 6616.
27. Nguyen, A. T.; Nguyen, L. T. M.; Nguyen, C. K.; Phan, T. T. N. T.
S. ChemCatChem 2014, 6, 815.
28. Odunola, O. A.; Woods, J. A. O. Synth. React. Inorg. Met.-Org.
Chem. 2001, 31, 1297.
29. Dell'Erba, C.; Novi, M.; Petrillo, G.; Tavani, C.; Bellandi, P.
Tetrahedron 1991, 47, 333.
30. Durrell, A. C.; Li, G.; Koepf, M.; Young, K. J.; Negre, C. F. A.;
Allen, L. J.; McNamara, W. R.; Song, H.; Batista, V. S.; Crabtree, R.
H.; Brudvig, G. W. J. Catal. 2014, 310, 37.
31. Lambert, J. B.; Liu, Z. J. Chem. Crystallogr. 2007, 37, 629.
32. Provent, C.; Chautemps, P.; Pierrea, J. L. Synth. Commun. 1995, 25,
1907.
33. Gong, F.; Wang, Q.; Chen, J.; Yang, Z.; Liu, M.; Li, S.; Yang, G.
Inorg. Chem. 2010, 49, 1658.
34. Lutz, R. E.; Dien, C. K. J. Org. Chem. 1956, 21, 551.
35. Dobosz, R.; Kolehmainen, E.; Valkonen, A.; Osmia1owski, B.;
Gawinecki, R. Tetrahedron 2007, 63, 9172.
36. Padwa, A.; Brookhart, T. J. Org. Chem. 1979, 44, 23.
37. Catalyst preparation and characterization: CuO/aluminosilicate
catalyst was prepared from CuCl2∙6H2O, aluminium nitrate and
Figure 3. Reusability test [Reaction conditions: acetylacetone (3
mmol), 4-bromobenzaldehyde (1 mmol), K3PO4 (3 mmol) and
CuO/aluminosilicate (20 mg, 8.0 mol%) at 100 C in 10 mL DMF
for 18 h].
The formation of CC bond between -diketone and aryl
halide was achieved using CuO/aluminosilicate catalyst.37 This
procedure is general, simple, ligand-free, air stable, efficient,
high yielding and safe. Both aryl bromides and chlorides gave

5
CH3) ppm; 13C-NMR (125 MHz, CDCl3) δ 191.3 (CO), 180.3
tetraethyl orthosilicate (TEOS) (Scheme S1) and characterized by
XRD, HR-TEM, SEM-EDX, XPS and BET analyses.
(CHO), 136.7, 133.2, 131.7, 130.8, 129.9, 128.7, 124.3, 29.5
Product analyses: The coupled products were analyzed by GC
(Shimadzu-2010) equipped with a 5% diphenyl and 95% dimethyl
polysiloxane, Restek-5 capillary column (60 m length, 0.32 mm dia)
and a flame ionization detector (FID). The column temperature was
220 oC. The temperatures of the injection port and FID were kept
constant at 250 C and 280 C, respectively during product analyses.
NMR spectra were recorded in Bruker 500 or 400 MHz NMR
spectrometer.
(CH3) ppm.
3-phenylpentane-2,4-dione (Table 2, entry 2): 1H-NMR (400 MHz,
DMSO-d6) δ 6.18 (s, 1H, CH), 7.25-7.46 (m, 6H, CH), 2.18 (s,
6H, CH3) ppm; 13C-NMR (100 MHz, DMSO-d6) δ 189.2 (CO),
115.5, 126.1, 129.4, 135.1, 162.6, 18.9 (CH3) ppm.
o
o
1
3-(2-formyl)phenylpentane-2,4-dione (Table 2, entry 10): H-NMR
(400 MHz, DMSO-d6) δ 9.94 (s, 1H, CHO), 6.13 (s, 1H, CH),
7.51 (d, 1H, CH, J=7.2 Hz), 7.62 (d, 1H, CH, J=7.2 Hz), 7.83
(d, 1H, CH, J=7.2 Hz), 7.93 (d, 1H, CH, J=7.2 Hz), 2.14 (s, 6H,
CH3) ppm; 13C-NMR (100 MHz, DMSO-d6) δ 193.2 (CO), 178.4
(CHO), 148.6 , 143.1, 141.9, 139.2, 137.3, 136.7, 134.5, 27.1
(CH3) ppm.
Procedure for -arylation of -diketones: In a typical procedure, a
mixture of 4-bromobenzaldehyde (0.184 g, 1 mmol), acetylacetone
(0.300 g, 3 mmol), CuO/aluminosilicate (20 mg, 8.0 mol%) and
o
K3PO4 (0.756 g, 3 mmol) in DMF (10 mL) was stirred at 100 C for
18 h. After completion of the reaction as indicated by GC, the
reaction mixture was centrifuged to recover the catalyst. The
centrifugate was treated with HCl (2 M) and extracted with
ethylacetate. The combined organic layers were dried over anhydrous
Na2SO4. The crude product was purified by column chromatography
using n-hexane/ethylacetate (8:2) eluent to obtain pure 3-(4-
formyl)phenylpentane-2,4-dione. Then it was characterized by 1H-
and 13C-NMR techniques.
Supplementary Material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.xxxx.xx.
3-(4-formyl)phenylpentane-2,4-dione (Table 2, entry 1): 1H-NMR
(500 MHz, CDCl3) δ 10.96 (s, 1H, CHO), 6.55 (s, 1H, CH), 7.49
(d, 2H, CH, J=7.6 Hz), 7.64 (d, 2H, CH, J=7.6 Hz), 2.36 (s, 6H,

Highlights
Research Highlights
ꢀ CuO/aluminosilicate is prepared from CuCl2·6H2O, Al(NO₃)₃·9H₂O and Si(OC₂H₅)₄
ꢀ α-Arylation of β-diketones is performed using CuO/aluminosilicate catalyst
ꢀ Scope is extended with various substituted aryl halides and β-diketones
ꢀ Chemoselectivity and heterogenity tests are demonstrated successfully
ꢀ The catalyst is heterogeneous and highly reusable