Copper/Iodine-Cocatalyzed C-C Cleavage of 1,3-Dicarbonyl Compounds Toward 1,2-Dicarbonyl Compounds

Article abstract of DOI:10.1002/ejoc.202000795

A new, general oxidative route to transformations of 1,3-dicarbonyl compounds to 1,2-dicarbonyl compounds by merging copper and I₂ catalysis is described. This method is applicable to broad 1,3-dicarbonyl compounds, including 1,3-diketones, 1,3-keto esters and 1,3-keto amides. Mechanistical studies show that the reaction is achieved via the C–C bond cleavage and CO release cascades.

Full text of DOI:10.1002/ejoc.202000795

European Journal of Organic Chemistry
Accepted Article
Accepted Article
Title: Copper/Iodine-cocatalyzed C-C Cleavage of 1,3-Dicarbonyl
Compounds Toward 1,2-Dicarbonyl Compounds
Authors: Li-Sha Chen, Lu-Bing Zhang, Yue Tian, Jin-Heng Li, and
Yong-Quan Liu
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.202000795
Link to VoR: https://doi.org/10.1002/ejoc.202000795
01/2020

10.1002/ejoc.202000795
European Journal of Organic Chemistry
COMMUNICATION
Copper/Iodine-cocatalyzed C-C Cleavage of 1,3-Dicarbonyl
Compounds Toward 1,2-Dicarbonyl Compounds
Li-Sha Chen*[a], Lu-Bing Zhang[a], Yue Tian[a], Jin-Heng Li*[b], and Yong-Quan Liu*[a]
[a]
L.-S. Chen, L.-B. Zhang, Y. Tian, Prof. Y. -Q. Liu
Occupational Medicine Monitoring Station
Institute of Occupational Medicine of Jiangxi
Nanchang 330006, China
Email: 529083967@qq.com, 529083967@qq.com
Homepage URL: http://www.jxszfs.com/plus/view.php?aid=891
Prof. Dr. J.-H. Li
[b]
Key Laboratory of Jiangxi Province for Persistent Pollutants Control and Resources Recycle
Nanchang Hangkong University
Nanchang 330063, China
Email: jhli@hnu.edu.cn
Homepage URL: http://huanhua.nchu.edu.cn/szll/jsxx/content_58147
Supporting information for this article is given via a link at the end of the document.
Abstract: A new, general oxidative route to transformations of 1,3-
dicarbonyl compounds to 1,2-dicarbonyl compounds by merging
copper and I2 catalysis is described. This method is applicable to
broad 1,3-dicarbonyl compounds, including 1,3-diketones, 1,3-keto
esters and 1,3-keto amides. Mechanistical studies show that the
reaction is achieved via the C-C bond cleavage and CO release
cascades.
obtained. Although a simple I2/DMSO oxidative catalytic system
has been developed by Yuan and Zhu,[5e] the system is limited to
1,3-diaryl 1,3-diketones. Moreover, the method required high
o
reaction temperature (150 C) and no desired reaction occurred
at 120 oC. Thus, development of new general and efficient routes
to conversion of broad 1,3-dicarbonyl compounds, such as 1,3-
diketones, 1,3-keto esters and 1,3-keto amides, is desirable.
Here, we report a new CuBr2/I2-cocatalyzed transformations of
various 1,3-dicarbonyl compounds, including 1,3-diketones, 1,3-
keto esters and 1,3-keto amides, to 1,2-dicarbonyl compounds,
using DMSO as the oxidant (Scheme 1b). The mechanistic
experiments provide evidence for this method which proceeds
through a sequence of C-C bond cleavage and CO release. This
reaction represents a general access to a wide range of 1,2-
dicarbonyl compounds, namely, 1,2-diketones, 1,2-keto esters
and 1,2-keto amides.
Dicarbonyl compounds, including 1,2-dicarbonyl compounds, are
important structural units of bioactive natural products,
pharmaceuticals and functional materials, as well as are
commonly functionalized and versatile synthetic intermediates in
synthesis.[1] Accordingly, seeking efficient, general methods for
the construction of 1,2-dicarbonyl frameworks has been a
longstanding goal. Such 1,2-dicarbonyl compounds are generally
prepared by (1) directly oxidation of unsaturated hydrocarbons
(e.g., alkynes, olefins)[2] or benzoin derivatives,[3] and (2)
substitution of oxalyl chlorides or α-keto acid chlorides.[4]
Alternatively, promising methods for conversions of 1,3-
dicarbonyl compounds to 1,2-dicarbonyl compounds through C–
C bond cleavage has emerged.[5] These approaches rely on an
oxidative C–C bond cleavage process via two strategies, the
oxidative transition-metal catalysis with releasing CO and the
oxidative I2 catalysis with discharging CO2 (Scheme 1a). However,
such approaches are rare, and most suffer from limited 1,3-
dicarbonyl compounds. In 2011, Zhang and coworkers found a
FeCl3/t-BuONO oxidative catalytic system that could efficiently
catalyzed transformation of 1,3-diketones to 1,2-diketones by
releasing CO2.[5a] Jiao and co-workers have also reported a CuBr-
catalyzed C-C bond cleavage of 1,3-diaryl 1,3-diketones for
producing 1,2-diaryl 1,2-diketones using sustainable O2.[5b] Zou
and
coworkers
have
established
an
efficiently
Scheme 1. Transformations of 1,3-Dicarbonyls to 1,2-Dicarbonyls.
CuBr/TEMPO/AcOH catalytic system which could be applicable
to both 1,3-diketones and 1,3-keto esters.[5c] In 2010, Itoh and
coworkers established a distinct mechanism method wherein
employed I2 as the catalyst and O2 as the oxidant under h
irradiation and basic conditions to enable conversion of 1,3-
diketones to 1,2-diketones through discharging CO2.[5d] They
have also an example of 1,3-keto ester, but lower reactivity was
We initiated our investigations with the use of the 1,3-
diphenylpropane-1,3-dione (1a) as the model substrate for
optimization of reaction conditions (Table 1). In the presence of
20 mol% CuBr2 and 100 mol% I2, the reaction of 1,3-diketoe 1a
o
was performed efficiently in DMSO at 120 C for 8 h, delivering
1
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10.1002/ejoc.202000795
European Journal of Organic Chemistry
COMMUNICATION
the desired benzil 2a in 94% yield (entry 1). As previously reported
by Yuan and Zhu,[5e] no desired reaction was observed in the
presence of 100 mol% I2 at 120 oC when omitting CuBr2 (entry 2).
Notably, the reaction could not occur without I2 (entry 9). These
results prove that emerging both CuBr2 and I2 as the cooperative
catalytic system is crucial for the reaction. Briefly screening the
loading of CuBr2 (entries 1 and 3-5) showed that 10 mol% of
CuBr2 was preferential since reducing the amount of CuBr2 to 5
mol% led to a decreased yield (68%; entry 3) and further
increasing the loading of CuBr2 to 100 mol% had no obvious
improvement on the yield (entry 5). Other catalysts, such as
Cu(OTf)2, CuBr, FeCl3, Fe(OTf)3 and BF3·Et2O, all were
competent in the reaction, and the copper salts displayed
especially high activity (entries 6-10). The amount of I2 was also
examined, and 20 mol% I2 was found to be the best option (entries
1 and 12-14). The reaction was sensitive to the reaction
17
18
19
20
21
22
in argon
95
H2O instead of DMSO
trace
42
DMSO (5 equiv)/H2O instead of DMSO
DMF or dioxane instead of DMSO
CuBr2 (10 mol%) and I2 (20 mol%)
0
90
CuBr2 (10 mol%), I2 (20 mol%) and 100 oC
64
[a] Reaction conditions: 1a (0.3 mmol), CuBr2 (20 mol%), I2 (100 mol%), DMSO
(anhydrous; 2 mL), 120 oC, air, and 8 h.
With optimized reaction conditions in hand, we turned our
attention to exploit the scope of this oxidative C-C bond cleavage
protocol with respect to 1,3-dicarbonyl compounds 1 (Table 2).
We found that a wide range of 1,3-dicarbonyl compounds 1,
including 3-diketones, 1,3-keto esters and 1,3-keto amides, could
be converted to the corresponding 1,2-dicarbonyl compounds in
good to excellent yields (entries 1-18). Two symmetrical 1,3-diaryl
1,3-diketones 1b-c engaged in the protocol smoothl to deliver 1,2-
diaryl 1,2-diketones 2b-c, respectively, in excellent yields (entries
1 and 2). The optimized conditions were also compatible to a wide
array of nonsymmetrical 1,3-diketones, such as 1,3-diaryl 1,3-
diketones (entries 3-11) and 1-aryl-3-alkyl 1,3-diketones 1m-o
(entries 12-14). A series of substituents, such as Me, MeO, Cl,
CO2Me, F and CF3, were well tolerated, and both the electronic
and steric hindrance properties affected the reaction to some
extent (entries 3-10). Two nonsymmetrical 1,3-ketones 1d-e
bearing an electron-donating substituent were highly reactive,
giving only 1,2-diketones 2d-e in excellent yields (entries 3 and 4),
which suggest the C-C bond cleavage via an intramolecular
process. While nonsymmetrical 1,3-ketones 1f-g having a para-
electron-withdrawing substituent (e.g., Cl, ester) accommodated
to the reaction with slight diminishing yields (entries 5 and 6), 1,3-
diketone 1h with an ortho-electron-withdrawing Cl substituent
exhibited a decreased reactivity and delivered 1,2-diketone 2h in
83% yield (entry 7). For 1,3-diketones 1i-k possessing two
different substituted aryl groups, the reaction also executed
efficiently (entries 8-10). Pleasedly, 1-phenyl-3-(thiophen-2-
yl)propane-1,3-dione 1l was a competent substrate to construct
heteroaryl-containing 1,2-diketone 2l (entry 11). In the case of 1-
aryl-3-alkyl 1,3-diketones 1m-o the reaction also proceeded
smoothly, albeit with slightly decreased reactivity (entries 12-14).
It was noted that 1,3-diketone 1o bearing a bulky tert-butyl group
was also transformed efficiently to 1,2-diketone 2o in 90% yield
(entry 14). However, 1-phenylpentane-2,4-dione (1p), a 1,3-
dialkyl 1,3-dicarbonyl compound, was inert, attributing to weak
electronic effect of alkyl groups to activate the corresponding 1,3-
dicarbonyl compound (entry 15). Strikingly, this protocol could be
applicable to 1,3-keto ester 1q and 1,3-keto amides 1r-t (entries
16-19). In the presence of CuBr2, I2 and DMSO, various 1,2-keto
ester 2q and 1,2-keto amides 2r-t were obtained in good yields.
o
o
temperatures: lowering the temperatures from 120 C to 100 C
o
or 80 C resulted in diminishing yields (entries 15 and 16). We
found that the reaction proceeded efficiently in air (entry 1) or
argon (entry 17). Other solvents, including H2O, DMF and dioxane,
had no reactivity (entries 18 and 20). The results suggest that
DMSO plays important roles in the reaction, which is also
supported by the results in a mixture of DMSO/H2O (entry 19),
probably attributing to oxidation property of DMSO. Gratifyingly,
use of 10 mol% CuB2 combined with 20 mol% I2 and DMSO at
120 oC proved to be optimal for the reaction (entries 21 and 22).
Table 1. Optimization of the Reaction Conditions[a]
.
Entry
1
Variation from the standard conditions
none
Isolated yield [%]
94
2
without CuBr2
trace
68
3
CuBr2 (5 mol%)
CuBr2 (10 mol%)
CuBr2 (100 mol%)
Cu(OTf)2 instead of CuBr2
CuBr instead of CuBr2
BF3·Et2O instead of CuBr2
FeCl3 instead of CuBr2
Fe(OTf)3 instead of CuBr2
without I2
4
90
5
92
6
93
7
89
8
55
9
83
10
11
12
13
14
15
16
78
trace
84
I2 (10%)
Table 2. Transformations of the 1,3-Dicarbonyl Compounds (1)[a]
.
I2 (20%)
92
I2 (40%)
93
at 100 oC
85
at 80 oC
62
2
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10.1002/ejoc.202000795
European Journal of Organic Chemistry
COMMUNICATION
18
19
Entry 1,3-Dicarbonyls 1
1,2-Dicarbonyls 2/Isolated Yield [%]
1
1s
2s/80%
2t/75%
1b
2b/90%
1t
2
[a] Reaction conditions: 1 (0.3 mmol), CuBr2 (10 mol%), I2 (20 mol%), DMSO
(anhydrous; 2 mL), 100 oC, air or argon, and 8 h. [b] >95% of 1p was recovered.
1c
2c/92%
3
4
As shown in Scheme 2, two other 1,3-diktones 1u-v were
examined [Eq (1)]. While 2-Me-substiuted substrate 1u was
converted smoothly to the desired 1,2-diketone 2a in 81% yield,
2,2-diMe-substituted substrate 1v had no reactivity. These results
suggest that the protocol might release CO, not CO2 that is often
discharged during the reported I2-catalyzed process.[5d-e] The
control experiment of a scale up to 1 g of 1a was performed
successfully, giving 2a in 95% yield [Eq (2)]. Notably, fresh yellow
phosphomolybdic acid-PdCl2 test paper turned dark-blue during
the reaction, which supported the formation of CO. No 18O-labeled
1,2-diketone 2a was obtained from the reaction with 18O-labeled
DMSO [Eq (3)]. Moreover, the reaction of 1,3-diketone 1a with
sulfinyldibenzene 3 afforded 1,2-diketone 2a in 31% yield
together with diphenylsulfane 4 in 15% yield, implying that DMSO
serves as an oxidation to initiate the reaction [Eq (4)]. These
results also suggest that the reaction is achieved by cleave the
C(sp3)-C(sp2) bonds.
1d
2d/96%
1e
2e/94%
5
6
1f
2f/90%
1g
2g/86%
7
8
1h
2h/83%
1i
2i/89%
9
1j
2j/91%
2k/93%
10
1k
11
12
1l
2l/87%
1m
Scheme 2. Control Experiments.
2m/80%
13
On the basis of the present results and the precedent results,[5]
we propose that the reaction is initiated by coordination of the Cu
catalyst with 1,3-diketone 1a to form the enol-[Cu] complex A.
Oxidative reaction of the complex A with iodine by DMSO affords
the 2-iodo-substituted 1,3-diketone-[Cu] complex intermediate B,
followed by replacement of the intermediate B with DMSO to
deliver the intermediate C. Decomposition of the intermediate C
produces the 1,2,3-triketone-[Cu] complex intermediate D, which
would sequentially undergo intramolecular C-C bond cleavage to
generate the carbonyl cation intermediate E. Finally,
decarbonylation of the intermediate E furnishes the desired 1,2-
diketone 2a and releases CO.
1n
2n/85%
14
1o
2o/90%
2p/trace
2q/81%
2r/83%
15[b]
1p
16
1q
17
1r
3
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10.1002/ejoc.202000795
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Scheme 3. Possible Mechanism.
In summary, we have developed a CuBr2 and I2 cooperative
catalysis for the oxidative C-C bond cleavage of 1,3-dicarbonyl
compounds to access synthetically valuable 1,2-dicarbonyl
compounds using DMSO as the oxidant. Considering the 1,2-
dicarbonyl compounds, high selectivity in the C-C bond cleavage
is achieved during the CO release process. Moreover, this
method is general to 1,3-dicarbonyl compounds, including 1,3-
diketones, 1,3-keto esters and 1,3-keto amides, with a broad
functional group tolerability, wherein use of a Cu catalyst to
enhance the activity of the iodine would spur conceptually new C-
C bond cleavage methodology.
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We thank the Key R&D Plan of Jiangxi Province
(20181BBG78034) for financial support.
Keywords: copper • iodine • oxidant • 1,3-dicarbonyls • 1,2-
dicarbonys
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COMMUNICATION
Entry for the Table of Contents
DMSO multi-taskings enabled a copper/I2-cocatalyzed transformations of 1,3-dicarbonyl compounds to 1,2-dicarbonyl compound is
depicted. This method is achieved through a sequence of C-C oxidative cleavage and CO release using DMSO as oxidant, oxygen
source and solvent, which is general to a wide range of 1,3-dicarbonyl compounds, including 1,3-diketones, 1,3-keto esters and 1,3-
keto amides, with excellent selectivity and a broad functional group tolerance.
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