Copper-catalyzed synthesis of 1,3,5-triarylpentane-1,5-diones from α,β-unsaturated ketones

Article abstract of DOI:10.1039/c5ra09155a

An efficient method for copper catalyzed synthesis of 1,3,5-triarylpentane-1,5-diones using α,β-unsaturated ketones as unique starting materials is described. The protocol offers several advantages such as simple, inexpensive reagents, mild reaction condi

Full text of DOI:10.1039/c5ra09155a

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Copper-catalyzed synthesis of 1,3,5-
triarylpentane-1,5-diones from a,b-unsaturated
ketones†
Cite this: RSC Adv., 2015, 5, 52121
*
Zheng Li, Gong Wen, Lili He, Jiasheng Li, Xianggui Jia and Jingya Yang
Received 16th May 2015
Accepted 9th June 2015
An efficient method for copper catalyzed synthesis of 1,3,5-triarylpentane-1,5-diones using a,b-
unsaturated ketones as unique starting materials is described. The protocol offers several advantages
such as simple, inexpensive reagents, mild reaction conditions and simple work-up procedure.
DOI: 10.1039/c5ra09155a
www.rsc.org/advances
materials with unpleasant odors that oen cause environment
pollution. In this work, a novel method for the synthesis of
Introduction
1,3,5-triarylpentane-1,5-diones is reported using a,b-unsatu-
rated ketones as the unique starting materials and inexpensive
cuprous iodide as the catalyst (Scheme 2).
Michael addition of a,b-unsaturated carbonyl compounds as
substrates is a benecial method to obtain 1,5-dicarbonyl
compounds,1 which are important synthetic building blocks
and have attracted the attention of many organic chemists.
The reported synthetic methods for 1,3,5-triarylpentane-1,5-
diones (Scheme 1) include: (1) using benzaldehyde and aceto-
phenone as the raw materials by Michael addition reaction;2 (2)
using a,b-unsaturated ketones (or benzaldehyde) and silyl enol
ethers as the starting materials in the presence of magnesium
chloride (or sodium hydroxide);3 (3) using a,b-unsaturated
ketones and diphenacyl suldes as the starting materials under
microwave irradiation.4 However, some of these methods use
air- and moisture-sensitive materials and require manipulation
using complex techniques; some of these methods use
Results and discussion
Initially, the synthesis of 1,3,5-triarylpentane-1,5-diones were
investigated using chalcone (1a) as a selected substrate. The
reaction was performed under the conditions of a wide range of
catalysts, bases and solvents.
It was found that the reaction desired to proceed under an
appropriate catalyst (Table 1), and the copper(I) salts, such as
CuCl, CuBr, CuI, CuOTf and CuCN, were revealed certain
activities for the synthesis of 1,3,5-triphenylpentane-1,5-dione
(2a) (Table 1, entries 2–6). Among them, the best yield was
obtained from CuI as a catalyst (Table 1, entry 4). However,
copper(II) salts and other metal compounds tested had no
activations for the reaction (Table 1, entries 7–9).
The bases were also indispensable for the reaction, and
NaOH, KOH, Ca(OH)2, Na2CO3, t-BuONa and t-BuOK were
tested for the reaction using CuI as a catalyst. It was found that
these bases had certain effects for the reaction (Table 1, entries
4, 10–14). Among them, NaOH was the most suitable base for
the reaction (Table 1, entry 4).
Meanwhile the solvents also played an important role in the
reaction. It was found that the yield of 2a could be signicantly
Scheme
1 The common synthetic methods for 1,3,5-triphe-
nylpentane-1,5-dione.
College of Chemistry and Chemical Engineering, Northwest Normal University,
Lanzhou, Gansu, 730070, P. R. China. E-mail: lizheng@nwnu.edu.cn
† Electronic supplementary information (ESI) available: Copies of IR, 1H and 13
C
Scheme 2 Synthesis of 1,3,5-triphenylpentane-1,5-dione from a,b-
NMR spectra of all compounds. See DOI: 10.1039/c5ra09155a
unsaturated ketone.
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Table 1 The effect of reaction conditions on the yield of 2aa
Table 2 Scope of a,b-unsaturated ketonesa
Entry
R1
R2
Yieldb (%)
Mp (ꢀC)
Entry
Catalyst
Base
Yieldb (%)
1
2
3
4
5
6
7
8
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
4-CH3C6H4
4-CH3OC6H4
4-CH3C6H4
4-CH3OC6H4
4-CH3OC6H4
4-CH3C6H4
3-CH3OC6H4
83
72
70
68
65
67
58
76
74
78
80
78
77
71
63–65
102–104
100–102
106–108
96–98
100–102
90–92
104–106
105–107
88–90
Oil
4-CH3C6H4
4-CH3OC6H4
2-CH3OC6H4
4-ClC6H4
2-ClC6H4
4-BrC6H4
C6H5
1
2
3
4
5
6
7
8
None
CuCl
CuBr
CuI
CuOTf
CuCN
Cu(OAc)2
FeCl2
AgCl
CuI
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
Ca(OH)2
Na2CO3
KOH
0
41
55
83
62
56
0
9
C6H5
0
0
10
11
12
13
14
4-CH3C6H4
4-CH3OC6H4
4-CH3C6H4
4-FC6H4
9
10
11
12
13
14
15
45
42
70
78
76
0
Oil
108–110
Oil
CuI
CuI
CuI
CuI
2,4-Cl2C6H3
t-BuONa
t-BuOK
None
15
4-ClC6H4
73
86–88
CuI
a
Reaction condition: 1a (0.2 mmol), base (0.6 mmol), and catalyst (0.02
16
C6H5
63
89–91
mmol) were stirred at 120 ꢀC in DMF–H2O (50 : 1) for 8 h under air.
b
Isolated yields.
a
Reaction condition: a,b-unsaturated ketones (0.2 mmol), NaOH (0.6
mmol), and CuI (0.02 mmol) in DMF (3 mL) and H2O (0.06 mL) were
b
stirred at 120 ꢀC for 8 h under air. Isolated yields.
elevated if addition of some water to organic solvents, such as
DMF and DMSO. However, the highest yield for 2a was obtained
in DMF–H2O (50 : 1). Other solvents, such as 1,4-dioxane,
PhMe, MeCN and EtOH in the presence of a certain amount of
water were found no effects on the reaction.
In addition, it was worthy of mentioning that keeping the
reaction under air condition at 120 ꢀC were also an essential
condition for the reaction.
Based on the above ndings, a series of a,b-unsaturated
ketones were investigated to synthesize 1,3,5-triarylpentane-1,5-
diones using CuI as a catalyst and NaOH as a base in DMF–H2O
(50 : 1) (Table 2). It was found that a,b-unsaturated ketones with
electron-donating (CH3, CH3O) or electron-withdrawing (F, Cl,
Br) groups on the aromatic rings could be successfully con-
verted to the corresponding products in good to excellent yields.
And the substituent groups at o-, m-, p-position on the aromatic
rings did not show strong steric effects. In addition, a,b-
unsaturated ketones bearing heterocyclyl such as thiophen-2-yl
could also converted into the corresponding product in good
yield (Table 2, entry 16).
A plausible mechanism was proposed for the synthesis of 1,3,5-
triarylpentane-1,5-diones (Scheme 3). First, a,b-unsaturated
ketones 1 were coordinated with Cu(I) to form Cu(I) complexes A.
Complexes A were attacked by the hydroxide ion in a conjugate
fashion to give the intermediates B. B were protonated to form b-
hydroxy ketones C.5 The base-induced retro-aldol reactions of C
would provide the corresponding benzaldehydes and acetophe-
nones. The resulting acetophenones could undergo base-catalyzed
conjugate additions to 1 to yield the observed compounds 2. And
the benzaldehydes subsequently were oxidized by air in the system
to benzoic acids, which could reduce the concentration of
Scheme 3 Plausible mechanism.
benzaldehydes and render the reaction equilibrium favorable to
the formation of 2.
Conclusions
A novel method for the synthesis of 1,3,5-triarylpentane-1,5-
diones using a,b-unsaturated ketones as unique starting
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materials and copper(I) as a catalyst under air condition has
been developed. The advantages of this protocol are the use of
inexpensive and non-toxic raw materials, mild conditions and
simple work-up procedure.
3-(2-Methoxyphenyl)-1,5-diphenylpentane-1,5-dione (2d)
1
White solid; Mp: 106–108 C; IR (KBr cmꢁ1): n 1680; H NMR
(400 MHz, CDCl3): d 7.99 (d, J ¼ 7.2 Hz, 4H, ArH); 7.52–7.54 (m,
2H, ArH); 7.43–7.46 (m, 4H, ArH); 7.15–7.30 (m, 2H, ArH); 6.82–
6.89 (m, 2H, ArH); 4.33–4.36 (m, 1H, CH); 3.77 (s, 3H, OCH3);
3.41–3.53 (m, 4H, 2CH2); 13C NMR (100 MHz, CDCl3): d 199.1,
157.0, 137.0, 132.8, 131.3, 128.4, 128.1, 127.6, 120.6, 110.7, 55.1,
43.0, 32.7.
ꢀ
Experimental
IR spectra were recorded using KBr pellets on an Alpha Centauri
1
FTIR spectrophotometer. H NMR and 13C NMR spectra were
obtained with Mercury-400 BB or Mercury-600BB instrument
using CDCl3 as solvent and Me4Si as the internal standard.
Melting points were observed in an electrothermal melting
point apparatus. a,b-Unsaturated ketones were prepared
according to literature procedure.6
3-(4-Chlorophenyl)-1,5-diphenylpentane-1,5-dione (2e)
Yellow solid; Mp: 96–98 ꢀC; IR (KBr, cmꢁ1): n 1674; 1H NMR (400
MHz, CDCl3): d 7.94 (d, J ¼ 7.2 Hz, 4H, ArH), 7.53–7.57 (m, 2H,
ArH), 7.42–7.46 (m, 4H, ArH), 7.22–7.23 (m, 4H, ArH), 4.04–4.07
(m, 1H, CH), 3.48 (dd, J ¼ 5.6, 16.8 Hz, 2H, CH2), 3.33 (dd, J ¼
6.0, 16.0 Hz, 2H, CH2); 13C NMR (100 MHz, CDCl3): d 198.1,
142.3, 136.8, 133.1, 132.3, 128.9, 128.7, 128.6, 128.0, 44.7, 36.5.
The general procedure for the preparation of 1,3,5-
triarylpentane-1,5-diones
The mixture of a,b-unsaturated ketones (0.2 mmol), NaOH
(0.6 mmol) and CuI (0.02 mmol) in DMF (3 mL) and H2O
(0.06 mL) was stirred under air at 120 ꢀC for 8 h. Aer the
completion of the reaction, the mixture was cooled to room
temperature, diluted with ethyl acetate and washed with satu-
rated sodium carbonate solution. The resulting organic phase
was dried over anhydrous magnesium sulfate, and concentrated
under reduced pressure. The residue was isolated by column
chromatography using petroleum ether and ethyl acetate
(30 : 1) as eluent to give pure product. The analytical data for
products are given below.
3-(2-Chlorophenyl)-1,5-diphenylpentane-1,5-dione (2f)
Yellow solid; Mp: 100–102 C; IR (KBr, cmꢁ1): n 1677; H NMR
1
ꢀ
(400 MHz, CDCl3): d 7.94 (d, J ¼ 7.6 Hz, 4H, ArH), 7.50–7.54 (m,
2H, ArH), 7.39–7.43 (m, 4H, ArH), 7.30–7.33 (m, 2H, ArH), 7.14–
7.18 (m, 1H, ArH), 7.08–7.11 (m, 1H, ArH), 4.48–4.55 (m, 1H,
CH), 3.51 (dd, J ¼ 7.2, 17.2 Hz, CH2), 3.43 (dd, J ¼ 6.8, 17.2 Hz,
CH2); 13C NMR (100 MHz, CDCl3): d 198.3, 140.8, 136.8, 133.7,
133.1, 130.0, 128.5, 128.4, 128.1, 127.7, 127.0, 42.9, 34.0.
3-(4-Bromophenyl)-1,5-diphenylpentane-1,5-dione (2g)
1,3,5-Triphenylpentane-1,5-dione (2a)
1
Red solid; Mp: 90–92 C; IR (KBr, cmꢁ1): n 1674; H NMR (400
ꢀ
Gray solid; Mp: 63–65 ꢀC; IR (KBr, cmꢁ1): n 1684; 1H NMR
(400 MHz, CDCl3): d 7.96 (d, J ¼ 7.2 Hz, 4H, ArH), 7.53–7.57
(m, 2H, ArH), 7.42–7.47 (m, 4H, ArH), 7.28 (d, J ¼ 13.6 Hz,
4H, ArH), 7.19–7.20 (m, 1H, ArH), 4.06–4.11 (m, 1H, CH), 3.55
(dd, J ¼ 7.2, 16.8 Hz, 2H, CH2), 3.37 (d, J ¼ 6.8, 16.4 Hz, 2H,
CH2); 13C NMR (100 MHz, CDCl3): d 198.5, 143.8, 137.0, 133.0,
128.6, 128.5, 128.1, 127.5, 126.7, 44.9, 37.2.
MHz, CDCl3): d 7.95 (d, J ¼ 6.8 Hz, 4H, ArH), 7.55–7.58 (m, 2H,
ArH), 7.44–7.47 (m, 4H, ArH), 7.39 (d, J ¼ 6.8 Hz, 2H, ArH), 7.18
(d, J ¼ 6.8 Hz, ArH), 4.04–4.07 (m, 1H, CH), 3.49 (dd, J ¼ 6.8, 16.8
Hz, 2H, CH2), 3.33 (dd, J ¼ 6.0, 16.8 Hz, 2H, CH2); 13C NMR (100
MHz, CDCl3): d 198.1, 142.8, 136.8, 133.2, 131.6, 129.3, 128.6,
128.1, 120.4, 44.6, 36.5.
1,5-Diphenyl-3-p-tolylpentane-1,5-dione (2b)
1,5-Bis-(4-methoxyphenyl)-3-phenylpentane-1,5-dione (2h)
White solid; Mp: 102–104 C; IR (KBr, cmꢁ1): n 1674; H NMR
1
ꢀ
1
Yellow solid; Mp: 104–106 C; IR (KBr, cmꢁ1): n 1680; H NMR
ꢀ
(400 MHz, CDCl3): d 7.95 (d, J ¼ 7.6 Hz, 4H, ArH), 7.52–7.57 (m,
2H, ArH), 7.42–7.46 (m, 4H, ArH), 7.17 (d, J ¼ 6.8 Hz, 2H, ArH),
7.08 (d, J ¼ 7.2 Hz, ArH), 4.02–4.05 (m, 1H, CH), 3.48 (dd, J ¼ 6.8,
16.4 Hz, 2H, CH2), 3.32 (dd, J ¼ 6.8, 16.4 Hz, 2H, CH2), 2.28 (s,
1H, CH3); 13C NMR (100 MHz, CDCl3): d 198.6, 140.7, 136.9,
136.1, 133.0, 129.2, 128.5, 128.1, 127.2, 45.0, 36.8, 21.0.
(400 MHz, CDCl3): d 7.85 (d, J ¼ 6.0 Hz, 4H, ArH), 7.17–7.27 (m,
9H, ArH), 4.03–4.06 (m, 1H, CH), 3.45 (dd, J ¼ 6.8, 16.4 Hz, 2H,
CH2), 3.30 (dd, J ¼ 4.8, 14.4 Hz, 2H, CH2), 2.39 (m, 6H, CH3); 13
C
NMR (100 MHz, CDCl3): d 198.2, 143.9, 143.8, 134.3, 129.2,
128.5, 128.2, 127.4, 126.5, 44.8, 37.2, 21.6.
3-(4-Methoxyphenyl)-1,5-diphenylpentane-1,5-dione (2c)
1,5-Bis(4-methoxyphenyl)-3-phenylpentane-1,5-dione (2i)
1
1
White solid; Mp: 100–102 C; IR (KBr, cmꢁ1): n 1677; H NMR White solid; Mp: 105–107 C; IR (KBr, cmꢁ1): n 1670; H NMR
(400 MHz, CDCl3): d 7.95 (d, J ¼ 7.6 Hz, 4H, ArH), 7.53–7.56 (m, (600 MHz, CDCl3): d 7.93 (d, J ¼ 8.4 Hz, 4H, ArH), 7.24–7.26 (m,
2H, ArH), 7.42–7.46 (m, 4H, ArH), 7.19 (d, J ¼ 8.4 Hz, 2H, ArH), 4H, ArH), 7.15–7.17 (m, 1H, ArH), 6.91 (d, J ¼ 9.0 Hz, ArH), 4.0–
6.81 (d, J ¼ 8.0 Hz, 2H, ArH), 4.00–4.04 (m, 1H, CH), 3.76 (s, 3H, 4.05 (m, 1H, CH), 3.84 (s, 6H, OCH3), 3.42 (dd, J ¼ 7.2, 16.2 Hz,
OCH3), 3.47 (dd, J ¼ 6.8, 16.4 Hz, 2H, CH2), 3.31 (dd, J ¼ 7.2, 16.8 2H, CH2), 3.27 (dd, J ¼ 6.6, 16.2 Hz, 2H, CH2); 13C NMR (100
Hz, 2H, CH2); 13C NMR (100 MHz, CDCl3): d 198.7, 158.2, 137.0, MHz, CDCl3): d 197.1, 163.4, 144.0, 130.4, 130.0, 128.5, 127.4,
ꢀ
ꢀ
135.8, 133.0, 128.5, 128.4, 128.1, 114.0, 55.2, 45.1, 36.5.
126.5, 113.6, 55.4, 44.6, 37.6.
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197.2, 147.8, 146.3, 139.6, 137.2, 135.1, 129.5, 128.9, 120.4,
108.3, 107.7, 100.9, 45.0, 37.0.
1,3,5-Tri-p-tolylpentane-1,5-dione (2j)
Yellow solid; Mp: 88–90 ꢀC; IR (KBr, cmꢁ1): n 1674; 1H NMR (400
MHz, CDCl3): d 7.85 (d, J ¼ 7.6 Hz, 4H, ArH), 7.23 (d, J ¼ 7.6 Hz,
4H, ArH), 7.16 (d, J ¼ 7.2 Hz, 2H, ArH), 7.07 (d, J ¼ 7.2 Hz, 2H,
ArH), 3.99–4.02 (m, 1H, CH), 3.43 (dd, J ¼ 7.2, 16.4 Hz, 2H, CH2),
3.28 (dd, J ¼ 6.8, 16.4 Hz, 2H, CH2), 2.36 (s, 6H, CH3), 2.27 (s,
3H, CH3); 13C NMR (100 MHz, CDCl3): d 198.2, 143.7, 140.9,
136.0, 134.5, 129.2, 129.2, 128.2, 127.2, 44.9, 37.0, 21.5, 20.9.
1,5-Diphenyl-3-thiophen-2-yl-pentane-1,5-dione (2p)
Gray solid; Mp: 89–91 ꢀC; IR (KBr, cmꢁ1): n 1686; 1H NMR (400
MHz, CDCl3): d 7.96 (d, J ¼ 7.6 Hz, 4H, ArH), 7.53–7.55 (m, 2H,
ArH), 7.43–7.46 (m, 4H, ArH), 7.10–7.11 (m, 1H, ThH), 6.88–6.89
(m, 2H, ThH), 4.42–4.45 (m, 1H, CH), 3.53 (dd, J ¼ 6.8, 16.8 Hz,
2H, CH2), 3.42 (dd, J ¼ 6.8, 16.8 Hz, 2H, CH2); 13C NMR (100
MHz, CDCl3): d 198.0, 147.4, 136.8, 133.1, 128.5, 128.1, 126.6,
124.2, 123.2, 45.5, 23.4.
1,3,5-Tris(4-methoxyphenyl)pentane-1,5-dione (2k)
Yellow liquid; IR (KBr, cmꢁ1): n 1670; 1H NMR (400 MHz,
CDCl3): d 7.94 (d, J ¼ 6.8 Hz, 4H, ArH), 7.18 (d, J ¼ 6.8 Hz, 2H,
ArH), 6.89 (d, J ¼ 6.8 Hz, 4H, ArH), 6.79 (d, J ¼ 6.8 Hz, 2H, ArH),
3.97–4.00 (m, 1H, CH), 3.83 (s, 6H, OCH3); 3.73 (s, 3H, OCH3),
3.40 (dd, J ¼ 6.4, 16.0 Hz, 2H, CH2), 3.23 (dd, J ¼ 5.6, 15.6 Hz,
2H, CH2); 13C NMR (100 MHz, CDCl3): d 197.3, 163.4, 158.1,
136.0, 130.4, 130.1, 128.4, 113.9, 113.7, 55.4, 55.1, 44.9, 37.0.
Acknowledgements
The authors thank the National Natural Science Foundation of
China (21162024, 21362034, 21462038) and Key Laboratory of
Eco-Environment-Related Polymer Materials for Ministry of
Education for the nancial support of this work.
1,5-Bis(4-methoxyphenyl)-3-p-tolylpentane-1,5-dione (2l)
Yellow liquid; IR (KBr, cmꢁ1): n 1670; 1H NMR (400 MHz,
CDCl3): d 7.94 (d, J ¼ 7.6 Hz, 4H, ArH), 7.16 (d, J ¼ 6.8 Hz, 2H,
ArH), 7.07 (d, J ¼ 7.2 Hz, 2H, ArH), 6.90 (d, J ¼ 7.2 Hz, 4H, ArH),
3.98–4.01 (m, 1H, CH), 3.83 (s, 6H, OCH3), 3.42 (dd, J ¼ 6.8, 16.0
Hz, 2H, CH2), 3.24 (dd, J ¼ 6.4, 16.0 Hz, 2H, ArH), 2.29 (s, 3H,
CH3); 13C NMR (100 MHz, CDCl3): d 197.3, 163.4, 140.9, 136.0,
130.4, 130.1, 129.2, 127.3, 113.7, 55.4, 44.8, 37.3, 21.0.
Notes and references
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3-(4-Fluorophenyl)-1,5-di-p-tolylpentane-1,5-dione (2m)
1
Yellow solid; Mp: 108–110 C; IR (KBr, cmꢁ1): n 1680; H NMR
ꢀ
(600 MHz, CDCl3): d 7.83 (d, J ¼ 8.4 Hz, 4H, ArH), 7.22–7.25 (m,
6H, ArH), 6.91–6.94 (m, 2H, ArH), 4.01–4.06 (m, 1H, CH), 3.43
(dd, J ¼ 7.2, 16.8 Hz, 2H, CH2), 3.27 (dd, J ¼ 7.8, 16.8 Hz, 2H,
CH2), 2.38 (s, 6H, CH3); 13C NMR (150 MHz, CDCl3): d 193.3,
139.2, 134.9, 134.8, 129.6, 124.5, 124.2, 124.1, 123.5, 110.6,
110.5, 40.1, 31.9, 16.8.
3-(2,4-Dichlorophenyl)-1,5-bis-(3-methoxyphenyl)pentane-1,5-
dione (2n)
Yellow liquid; IR (KBr, cmꢁ1): n 1680; 1H NMR (600 MHz,
CDCl3): d 7.53–7.55 (m, 2H, ArH), 7.46–7.47 (m, 2H, ArH), 7.33–
7.36 (m, 3H, ArH), 7.24–7.25 (m, 1H, ArH), 7.15–7.17 (m, 1H,
ArH), 7.08–7.10 (m, 2H, ArH), 4.45–4.50 (m, 1H, CH), 3.82 (s, 6H,
2OCH3), 3.49 (dd, J ¼ 7.2, 17.4 Hz, 2H, CH2), 3.40 (dd, J ¼ 7.2,
17.4 Hz, 2H, CH2); 13C NMR (150 MHz, CDCl3): d 198.1, 160.0,
139.7, 138.1, 134.6, 133.0, 130.0, 129.9, 129.5, 127.5, 121.0,
120.2, 112.4, 55.7, 43.1, 33.7.
2 (a) H. Takahashi, T. Arai and A. Yanagisawa, Synlett, 2006, 2833–
2835; (b) A. Yanagisawa, H. Takahashi and T. Arai, Tetrahedron,
2007, 63, 8581–8585; (c) G. C. Das, M. B. Hursthouse,
K. M. A. Malik, M. M. Rahman, M. T. Rahman and T. Olsson,
J. Chem. Crystallogr., 1994, 24, 511–515; (d) M. Nagaraj,
M. Boominathan, S. Muthusubramanian and N. Bhuvanesh,
Org. Biomol. Chem., 2011, 9, 4642–4652.
3-Benzo[1,3]dioxol-5-yl-1,5-bis(4-chlorophenyl)pentane-1,5-
dione (2o)
Yellow solid; Mp: 86–88 ꢀC; IR (KBr, cmꢁ1): n 1681; 1H NMR (600
MHz, CDCl3): d 7.87 (d, J ¼ 8.4 Hz, 4H, ArH), 7.41 (d, J ¼ 8.4 Hz,
4H, ArH), 6.74 (s, 1H, ArH), 6.67 (s, 2H, ArH), 5.88 (s, 2H, CH2),
3.90–3.95 (m, 1H, CH), 3.39 (dd, J ¼ 7.2, 16.8 Hz, 2H, CH2), 3.23 3 (a) K. Miura, T. Nakagawa and A. Hosomi, Synlett, 2003, 2068–
(dd, J ¼ 7.2, 16.8 Hz, 2H, CH2); 13C NMR (150 MHz, CDCl3): d
2070; (b) A. Marx and H. Yamamoto, Angew. Chem., Int. Ed.,
52124 | RSC Adv., 2015, 5, 52121–52125
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