Oxidative Coupling of 1,3-Dicarbonyl Compounds by Cerium(IV) Ammonium Nitrate

Article abstract of DOI:10.1080/00397910903161876

A fast, mild, and highly efficient method for the intermolecular coupling of 1,3-dicarbonyl compounds using cerium ammonium nitrate in CH ₃CN/CH₃OH/H₂O has been described. The procedure provided a convenient method for the synthesis of 1,4-diketone derivatives with excellent yields (up to 96%) and powerful evidence for the oxidation mechanism mediated by cerium ammonium nitrate. Copyright

Full text of DOI:10.1080/00397910903161876

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Oxidative Coupling of 1,3-Dicarbonyl
Compounds by Cerium(IV) Ammonium
Nitrate
Jianan Song a , Hao Zhang a , Xianjun Chen b , Xinsheng Li a c
Dongcheng Xu a c
&
a College of Chemistry and Life Science, Zhejiang Normal University,
Jinhua, China
b Chuyang Honors College, Zhejiang Normal University, Jinhua, China
c Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces,
Institute of Physical Chemistry, Zhejiang Normal University, Jinhua,
China
Published online: 17 May 2010.
To cite this article: Jianan Song , Hao Zhang , Xianjun Chen , Xinsheng Li & Dongcheng Xu (2010)
Oxidative Coupling of 1,3-Dicarbonyl Compounds by Cerium(IV) Ammonium Nitrate, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
40:12, 1847-1855, DOI: 10.1080/00397910903161876
To link to this article: http://dx.doi.org/10.1080/00397910903161876
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Synthetic Communications1, 40: 1847–1855, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910903161876
OXIDATIVE COUPLING OF 1,3-DICARBONYL
COMPOUNDS BY CERIUM(IV) AMMONIUM NITRATE
Jianan Song,1 Hao Zhang,1 Xianjun Chen,2 Xinsheng Li,1,3
and Dongcheng Xu1,3
1College of Chemistry and Life Science, Zhejiang Normal University,
Jinhua, China
2Chuyang Honors College, Zhejiang Normal University, Jinhua, China
3Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces,
Institute of Physical Chemistry, Zhejiang Normal University, Jinhua, China
A fast, mild, and highly efficient method for the intermolecular coupling of 1,3-dicarbonyl
compounds using cerium ammonium nitrate in CH3CN/CH3OH/H2O has been described.
The procedure provided a convenient method for the synthesis of 1,4-diketone derivatives
with excellent yields (up to 96%) and powerful evidence for the oxidation mechanism
mediated by cerium ammonium nitrate.
Keywords: Cerium ammonium nitrate; coupling reaction; 1,3-dicarbonyl compound; radical reaction
INTRODUCTION
Carbon–carbon bond-formation reaction is considered to be one of the most
important reactions in the organic synthesis. Carbon–carbon bond formation was
usually carried out by coupling the double-bond functions of the compounds, such
[3]
as coupling of aldehydes,[1] ketones,[2] and imines with reducing agents including
magnesium,[4] aluminum,[5] and samarium.[6] Only a few examples of oxidative
reagents in coupling reaction were reported. On the other hand, cerium(IV)
ammonium nitrate (CAN), an efficient single-electron-transfer (SET) reagent, was
studied in the carbon–carbon bond-forming reactions[7] and deprotection reactions[8]
extensively. Most recently, Zhang and coworkers[9] reported that b-ketoesters could
be converted to corresponding carboxylic acids using CAN as an oxidative reagent in
42–95% yield. They assumed that the active cation radical 1 was the key intermediate
in the oxidation (Scheme 1). We thought that if the cation radical 1 exists in the reac-
tion system, the dimer of 1 could be formed under an appropriate condition, and the
dimers are useful intermediates in the synthesis of cyclopentanone and furan deriva-
tives. These encouraged us to explore the intermolecular coupling of 1,3-dicarbonyl
compounds using CAN as oxidative reagent to get the dimer of 1. In this article, we
Received January 21, 2009.
Address correspondence to Xinsheng Li, College of Chemistry and Life Science, Zhejiang Normal
University, Jinhua, China. E-mail: sky33@zjnu.cn
1847

1848
J. SONG ET AL.
Scheme 1. The key intermediate in the oxidative reaction.
describe a convenient and highly efficient method for the intermolecular coupling of
1,3-dicarbonyl using CAN as an oxidative reagent to get 1,4-diketone derivatives
with excellent yield (up to 96%).
RESULTS AND DISCUSSION
The reaction temperature is critical for the capture of an active intermediate in
the reaction. Moreover, the using of excessive CAN in the coupling reaction
decreased the desired product.[10] After many trials, the best result of the coupling
reaction was obtained by using acetylacetone (2a) as a typical substrate in the
presence of 1.1 eq. of CAN at ꢀ20 ꢁC for 15 min, and 80% yield was achieved under
these conditions.
With the optimum reaction conditions in hand, the coupled reactions of vari-
ous benzoyl acetone derivatives and ethyl benzoylacetate derivatives were explored.
The results are summarized in Table 1. The results showed that diketones are more
reactive than ketoesters, and the coupling rate of diketones is greater than ketoesters.
Completing the reaction of diketones needs 15 min, but 4 h was needed for the coup-
ling of ketoesters (Table 1, entries 1–10 and 11–14). In addition, the electronic nature
on the phenyl ring of the ketoester had remarkable influence on the yield of the reac-
tion. Better yields were achieved with electron-donating group on the phenyl ring,
while the para-substituent of electron-withdrawing provided lesser yield (Table 1,
entry 12). The substituent position had small effect on the yields of the coupling
of diketones. The electron-withdrawing group on the phenyl ring reduced the yield,
and the electron-donating group on the phenyl ring improved the yields (Table 1,
entries 4, 5, 9, and 10). The substrates with both electron-donating groups and
electron-withdrawing groups could achieve satisfying yield. Cross-coupling reaction
of diketone and ketoester was unsuccessful (Scheme 2). The cross-coupling reaction
gave benzoic acid derivatives, which were determined by gas chromatographic (GC)
analysis, and the unreactive ketoester was recovered. The result is reasonable accord-
ing the reported mechanism.[9a] One equivalent of CAN first oxidized a diketone to
give intermediate 4, and the other equivalent of CAN further oxidized 4 to provide a
benzoic acid derivative as the main product. Only the reaction of 2 g and 2 m, a Cl
substituent on the para- position of phenyl group, provided the cross-coupling
product with 10% yield in the cross-coupling reaction of diketone and ketoester.
Based on the experimental data and related report,[9a,11] the possible mechanism
is shown in Scheme 3. The enol of the 1,3-dicarbonyl compound was first oxidized by
Ce(IV) to form the cation radical 1. The proton of methene of the diketone has greater
acidity than the ketoester, so the diketone could change more easily into 4 than the
ketoester, which was further coupled to provide product 3 with lack of enough

OXIDATIVE COUPLING
1849
Table 1. CAN-mediated oxidative coupling reaction of 1,3-diketonea
Entry
1
Product
Yield (%)b
80
88
82
96
96
83
82
85
2
3
4
5
6
7
8
9
83
(Continued )

1850
J. SONG ET AL.
Table 1. Continued
Entry
10
Product
Yield (%)b
79
11
12
13
14
83c
91c
37c
35c
aReactions performed with the 1.1 eq. of CAN in CH3CN=CH3OH=H2O (2=1=1,
v=v=v) at ꢀ20 ꢁC for 15 min.
bIsolated yield.
cReactions performed with the 1.1 eq. of CAN in CH3CN=CH3OH=H2O (2=1=1,
v=v=v) at ꢀ20 ꢁC for 4 h.
CAN. The intermediate 4 was formed by oxidizing of diketone at first in the cross-
coupling of diketone and ketoester, and the ketoester was not oxidized at this state,
so the excessive CAN was further oxidized 4 to give benzoic acid derivative. The
internal ligand transfer of nitrate played an important role in the reaction, which
Scheme 2. Cross-coupling of diketones and ketoesters.

OXIDATIVE COUPLING
1851
Scheme 3. The mechanism of oxidative coupling of 1,3-dicarbonyl by CAN.
led to the completion of the reaction.[9a] After formation of 5, which could be trans-
ferred to the product 3 under the lack of enough CAN, the preproduct was transferred
to product by the action of H2O of the system, which reduced the by-product,
improved the yield, and accelerated the rate of the coupling reaction.
CONCLUSIONS
In conclusion, a fast, mild, and highly efficient method for the conversion of
1,3-dicarbonyl compounds to the corresponding dimers using CAN in CH3CN=
CH3OH=H2O has been developed. The procedure provided an alternative
convenient route for the synthesis of polycarbonyl compounds by using nontoxic
and inexpensive Ce(IV) under mild conditions. Aside from the coupling products,
the procedure offered a powerful proof of the oxidation mechanism by CAN.
Further exploration of the synthetic utility of this new reaction is under way.
EXPERIMENTAL
Melting points are determined by using an electrothermal melting-point
1
apparatus and are uncorrected. H NMR and 13C NMR spectra were recorded on
a Bruker Avance 400 spectrometer, and chemical shift values are recorded in d units
(ppm) relative to Me4Si as internal standard. Elemental analyses are performed on
an elemental Vario EL III CHNS analyzer.
General Procedure of CAN-Mediated Oxidative Coupling Reaction
of 1,3-Dicarbonyl Compounds
A solution of CAN (3 g, 5.5 mmol) in H2O (10 mL) was added dropwise to a
solution of 2a (0.512 g, 5 mmol) in CH3CN (20 mL) and CH3OH (10 mL) over a
period of 5 min at ꢀ20 ꢁC. The mixture was stirred at the same temperature for
another 10 min, and H2O was added. The organic layer was separated, and the
aqueous layer was extracted with EtOAc (2 ꢂ 15 mL). The combined organic phase
was washed with H2O (15 mL) and dried over Na2SO4. After removal of the solvent

1852
J. SONG ET AL.
under reduced pressure, the residue was recrystallized (EtOAc–hexane) to afford a
white solid.
1
3,4-Diacetylhexane-2,5-dione (3a). White solid. Mp 190–191 ꢁC. H NMR
(CDCl3): 16.76 (s, 2H), 2.00 (s, 12H). 13C NMR (CDCl3): 192.6, 108.1, 23.5. Anal.
calcd. for C10H14O4: C, 60.59; H, 7.12. Found: C, 60.50; H, 7.18.
1
3,4-Dibenzoylhexane-2,5-dione (3b)[12]. White solid. Mp 188–191 ꢁC. H
NMR (CDCl3): 8.19–8.17 (d, J ¼ 8 Hz, 4H), 7.69–7.65 (m, 2H), 7.59–7.55 (m, 4H),
5.92 (s, 2H), 2.08 (s, 6H). 13C NMR (CDCl3): 200.1, 194.8, 136.6, 134.1, 77.3,
77.0, 76.7, 62.5, and 30.6. Anal. calcd. for C20H18O4: C, 74.52; H, 5.63. Found: C,
74.60; H, 5.65.
3,4-Bis(2-methylbenzoyl)hexane-2,5-dione (3c). White solid. Mp 188–
1
190 ꢁC. H NMR (CDCl3): 17.3 (s, 2H), 7.22–7.18 (m, 2H), 7.09–7.04 (m, 4H),
6.83–6.81 (m, 2H), 2.38 (s, 6H), 1.44 (s, 6H).13C NMR (CDCl3): 197.3, 188.1,
137.8, 135.1, 131.3, 129.7, 127.6, 124.6, 108.7, 24.9, and 19.0. Anal. calcd. for
C22H22O4: C, 75.41; H, 6.33. Found: C, 75.52; H, 6.40.
3,4-Bis(3-methylbenzoyl)hexane-2,5-dione (3d). White solid. Mp 185–
1
188 ꢁC. H NMR (CDCl3): 7.99–7.95 (m, 4H), 7.47–7.43 (m, 4H), 5.89 (s, 2H),
2.47 (s, 6H), 2.07 (s, 6H). 13C NMR (CDCl3): 200.2, 195.0, 138.9, 136.7, 134.8,
129.6, 128.9, 128.9, 126.5, 62.5, 30.5, and 21.4. Anal. calcd. for C22H22O4: C,
75.41; H, 6.33. Found: C, 75.45; H, 6.45.
3,4-Bis(4-methylbenzoyl)hexane-2,5-dione (3e). White solid. Mp 205–
1
207 ꢁC. H NMR (CDCl3): 8.07–7.34 (dd, J1 ¼ 8 Hz, J2 ¼ 285 Hz, 8H), 5.86 (s, 2H),
2.45 (s, 6H), 2.07 (s, 6H). 13C NMR (CDCl3): 200.2, 194.2, 145.0, 134.2, 129.7, 129.3,
62.3, 30.4, and 21.71. Anal. calcd. for C22H22O4: C, 75.41; H, 6.33. Found: C, 75.52;
H, 6.44.
3,4-Bis(3-chlorobenzoyl)hexane-2,5-dione (3f). White solid. Mp 176–
177 ꢁC. 1H NMR (CDCl3): 8.11–8.08 (m, 4H), 7.65–7.63 (m, 2H), 7.55–7.51
(m, 2H), 5.80 (s, 2H), 2.06 (s, 6H). 13C NMR (CDCl3): 199.3, 193.6, 138.2, 135.5,
134.0, 130.4, 129.1, 127.3, 62.7, and 30.4. Anal. calcd. for C20H16Cl2O4: C, 61.40;
H, 4.12. Found: C, 61.38; H, 4.18.
3,4-Bis(4-chlorobenzoyl)hexane-2,5-dione (3g). White solid. Mp 190–
1
193 ꢁC. H NMR (CDCl3): 17.40 (s, 2H), 7.33–7.27 (dd, J1 ¼ 8.8 Hz, J2 ¼ 17.5 Hz,
8H), 5.78 (s, 2H), 2.07 (s, 6H). 13C NMR (CDCl3): 199.4, 194.7, 137.6, 131.9,
130.6, 129.9, 62.3, and 30.1. Anal. calcd. for C20H16Cl2O4: C, 61.40; H, 4.12. Found:
C, 61.45; H, 4.08.
3,4-Bis(4-bromobenzoyl)hexane-2,5-dione (3h). White solid. Mp 196–
197 ꢁC. 1H NMR (CDCl3): 8.05–7.71 (dd, J1 ¼ 8.6 Hz, J2 ¼ 127.7 Hz, 8H), 5.79
(s, 2H), 2.04 (s, 6H).13C NMR (CDCl3): 199.5, 193.8, 135.3, 132.4, 130.7, 129.6,
62.4, and 30.4. Anal. calcd. for C20H16Br2O4: C, 50.03; H, 3.36. Found: C, 50.12;
H, 3.40.
3,4-Bis(4-(trifluoromethyl)benzoyl)hexane-2,5-dione (3i). White solid.
Mp 180–183 ꢁC. 1H NMR (CDCl3): 17.2 (s, 2H), 7.55–7.33 (dd, J1 ¼ 8.2 Hz,

OXIDATIVE COUPLING
1853
J2 ¼ 80.0 Hz, 8H), 2.17 (s, 6H).13C NMR (CDCl3): 195.1, 180.9, 151.5, 142.6, 138.1,
135.7, 127.3, 125.6, 122.3, 110.0, 97.3, 67.9, 66.4, 34.2, 30.3, 26.1, and 21.1. Anal.
calcd. for C22H16F6O4: C, 57.65; H, 3.52. Found: C, 57.71; H, 3.49.
3,4-Bis(4-fluorobenzoyl)hexane-2,5-dione (3j). White solid. Mp 171–
1
173 ꢁC. H NMR (CDCl3): 17.4 (s, 2H), 7.42–6.96 (dd, J1 ¼ 8.6 Hz, J2 ¼ 151.6 Hz,
8H), 2.06 (s, 6H).13C NMR (CDCl3): 200.1, 193.1, 167.7, 165.1, 132.1, 131.9,
130.4, 116.4, 116.2, 62.4, 30.5, and 24.9. Anal. calcd. for C20H16F2O4: C, 67.04; H,
4.50. Found: C, 67.09; H, 4.46.
Diethyl-2,3-dibenzoylsuccinate (3k). White solid. Mp 127–129 ꢁC. 1H
NMR (CDCl3): 8.19–7.46 (m, 10H), 5.62 (s, 1H), 5.55 (s, 1H), 4.15–4.12 (m, 2H),
3.98–3.95 (m, 2H), 1.15–1.13 (m, 3H), 0.99–0.95 (m, 3H); 13C NMR (CDCl3):
194.0, 193.1, 167.5, 133.8, 167.1, 133.7, 130.1, 129.4, 129.3, 128.7, 128.6, 128.5,
62.0, 54.2, 53.2, 13.8, 13.6. Anal. calcd. for C22H22O6: C, 69.10; H, 5.80. Found:
C, 68.45;H, 5.63.
Diethyl-2,3-bis(4-methylbenzoyl)succinate (3l). White solid. Mp 164–
1
166 ꢁC. H NMR (CDCl3): 8.05–7.12 (m, 8H), 5.58 (s, 1H), 5.51 (s, 1H), 4.17–4.11
(m, 2H), 3.99–3.94 (m, 2H), 2.43 (s, 3H), 2.41 (s, 3H), 1.18–1.14 (m, 3H),
0.99–0.96 (m, 3H); 13C NMR (CDCl3): 193.5, 192.6, 167.7, 167.2, 144.7, 144.5,
133.7, 133.3, 130.2, 130.0, 129.6, 129.5, 129.4, 129.3, 129.2, 61.9, 54.0, 53.2, 21.7,
13.8, 13.6. Anal. calcd. for C24H26O6: C, 70.23; H, 6.38. Found: C, 70.20; H, 6.33.
Diethyl-2,3-bis(4-chlorobenzoyl)succinate (3m). White solid. Mp 161–
163 ꢁC. 1H NMR (CDCl3,): 8.13–7.49 (dd, J1 ¼ 6.7 Hz, J2 ¼ 247.1 Hz, 8H), 5.54
(s, 2H), 4.01–3.96 (m, 4H), 1.01–0.97 (m, 6H); 13C NMR (CDCl3): 192.8, 166.8,
140.4, 134.5, 130.8, 128.9, 62.2, 53.1, 13.6. Anal. calcd. for C22H20Cl2O6: C, 58.55;
H, 4.47. Found: C, 58.69; H, 4.53.
Diethyl-2,3-bis(4-bromobenzoyl)succinate (3n). White solid. Mp 159–
161 ꢁC. 1H NMR (CDCl3): 8.04–7.66 (dd, J1 ¼ 8.3 Hz, J2 ¼ 146.2 Hz, 8H), 5.53
(s, 2H), 4.01–3.96 (m, 4H), 1.01–0.98 (t, 6H); 13C NMR (CDCl3): 193.0, 166.7,
134.9, 131.9, 130.9, 129.2, 62.2, 53.0, 13.7. Anal. calcd. for C22H20Br2O6: C, 48.91;
H 3.73. Found: C, 47.76; H 3.69.
Ethyl-2,3-bis(4-chlorobenzoyl)-4-oxopentanoate. White solid. Mp 208–
1
210 ꢁC. H NMR (CDCl3): 8.12–8.00 (m, 4H), 7.51–7.29 (m, 4H), 5.82–5.69 (dd,
J1 ¼ 10.8 Hz, J2 ¼ 42.2 Hz, 2H), 4.16–4.11 (m, 2H), 2.07 (s, 3H), 1.18–1.12 (m,
3H); 13C NMR (CDCl3): 198.9, 193.2, 192.7, 167.1, 140.8, 134.9, 130.8, 130.7,
130.5, 129.4, 129.1, 128.9, 62.3, 54.1, 45.9, 30.2, 13.8. Anal. calcd. for C22H20Br2O6:
C, 59.87; H, 4.31. Found: C, 59.83; H, 4.29.
ACKNOWLEDGMENTS
This work was supported by National Natural Science Foundation of China
(Nos. 20572101 and 20672101) and Xin Miao Talent Scheme of Zhejiang (No.
2008R40G2030026).

1854
J. SONG ET AL.
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