Novel one-pot procedure for the synthesis of 1,2-diketones

Article abstract of DOI:10.1080/00397910802398264

A simple and convenient one-pot procedure is reported for the synthesis of 1,2-diketones from corresponding benzoin-type condensation reaction of aromatic aldehydes in water with N,N-dialkylbenzimidazolium salt as condensation catalyst and ferric chloride as oxidizing reagent. Copyright Taylor & Francis Group, LLC.

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Novel One-Pot Procedure for
the Synthesis of 1,2-Diketones
Xiaobi Jing a , Xin Pan a , Zhen Li a , Yaocheng Shi a
& Chaoguo Yan a
a College of Chemistry and Chemical Engineering,
Yangzhou University, Yangzhou, China
Published online: 08 Jan 2009.
To cite this article: Xiaobi Jing , Xin Pan , Zhen Li , Yaocheng Shi & Chaoguo Yan
(2009): Novel One-Pot Procedure for the Synthesis of 1,2-Diketones, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 39:3, 492-496
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Synthetic Communications1, 39: 492–496, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910802398264
Novel One-Pot Procedure for the Synthesis
of 1,2-Diketones
Xiaobi Jing, Xin Pan, Zhen Li, Yaocheng Shi, and Chaoguo Yan
College of Chemistry and Chemical Engineering, Yangzhou University,
Yangzhou, China
Abstract: A simple and convenient one-pot procedure is reported for the
synthesis of 1,2-diketones from corresponding benzoin-type condensation
reaction of aromatic aldehydes in water with N,N-dialkylbenzimidazolium salt
as condensation catalyst and ferric chloride as oxidizing reagent.
Keywords: Benzils, benzimisazolium catalysts, benzoin condensation, 1,2-diketones
INTRODUCTION
Benzils have received a great deal of attention because of their applications
as photosensitive reagents in photocurable coatings, as starting materials
in organic and pharmaceutical synthesis,[1] and also as biologically active
compounds.[2] Conventionally, benzils are prepared by several different
methods, such as coupling of acid chlorides with SmI2,[3] oxidation of
mono ketones with SeO2, and oxidation of acetylenes with NaIO4=
RuO2,[4] Tl(NO3)3,[5] and KMnO4.[6] Some organooxidants, such as
4-MeO-2,2,6,6-tetramethylpiperidinyl-l-oxy
(TEMPO),[7a]
(4-AcNH-
TEMPO)-OTs-TsOH,[7b] 4-phCO2-TEMPO,[7c] n-Bu4N[MoO(O)2C5H4-
N(O)O2)],[8] and H2O2-[C5H5N(CH2)15CH3]3{PO4[W(O)(O2)]4},[9] can also
oxidize 1,2-diols to 1,2-diketones; however, these oxidants are complex
and expensive. Meanwhile, benzils are able to be prepared by the oxidation
of corresponding benzoins with inorganic oxidants such as CuSO4=Py,
Received May 10, 2008.
Address correspondence to Xiaobi Jing, College of Chemistry and Chemical
Engineering, Yangzhou University, Yangzhou 225002, China. E-mail: jingxiaobi@
yahoo.com.cn
492

Synthesis of 1,2-Diketones
493
Bi2O3=Hþ, and HNO3 in aq. solution[10] and RuO4.[11] All these methods
have drawbacks in terms of expensive regents, difficult reaction conditions,
and low yields. Surprisingly, to our knowledge, there are no examples of sim-
ple synthesis of benzils directly from aldehydes in one pot. We report herein
a simple and convenient procedure for the synthesis of a variety of benzils
from corresponding aldehydes.
RESULTS AND DISCUSSION
In 2006, Iwamoto et al.[12] reported that benzion condensation reaction
can be catalyzed by N,N-dialkylbenzimidazole in water to yield
a-hydroxy ketones. We repeated this reaction and found that the yield
of proucts is usually very low (Scheme 1).
When we studied this reaction, it was found that one of the by-
product is benzils in the same system. Unfortunately, the yield of benzils
was only 10% when the reaction was carried out in a nitrogen atmos-
phere. It can be concluded that in the reaction process, some of a-
hydroxy ketones was oxidized in air to give benzil. Hence, It is possible
to add one oxidant to the system and make the oxidation reaction
complete. We chose FeCl3 ꢀ 6H2O as the oxidizing agent and directly
added it into the reaction mixture after the catalytic benzoin conden-
sation was finished. The good yield (71%) of the benzil was observed
after workup.
To optimize the reaction condition, we examined this one-pot reac-
tion by varying benzimidazolium salts, solvent, and time and using the
reaction of benzaldehyde as a comparing reference (Scheme 2). The
results are summarized in Tables 1 and 2.
From Table 1, it can be seen that as the number of the carbon atoms
of the N-substituent increased from two to eight, the yields of benzil
improved gradually. The yield was slightly reduced when the carbon
Scheme 1. Benzoin condensation catalyzed by benzimidazolium salt.

494
X. Jing et al.
Scheme 2. Synthesis of benzils in one-pot reaction.
atom number increased to more than eight. So, 2e is the best catalyst in
the reaction. We also found that the reaction takes place more smoothly
than in the other organic solvent (Table 2).
Under optimized conditions (catalyzed by 2e in water), the reac-
tivity of a series of aromatic aldehydes in this reaction was examined;
the results are summarized in Table 3. From the table it can be seen
that aromatic aldehyde containing chloro-, bromo-, and methyl sub-
stituent afforded the desired benzils in higher yields. The reactions
of 3-nitrobenzaldehyde or 4-nitrobenzaldehyde and p-hydroxyl benzal-
dehyde were considerably slow, and the yields of benzils were much
lower. Furfural only gave furil in about 5% yield, mainly because of
its easily oxidation by FeCl3.
In conclusion, we developed a one-pot synthesis of benzils by the
dimeric reaction of aldehydes with benzimidazolium salt as catalyst
and ferric chloride as oxidant. This kind of reaction under the mild
conditions opens a novel green entry to synthesis of benzils by a simple
procedure.
Table 1. Synthesis of benzils catalyzed by benzimidazolium salts
Entry
Catalyst R
CH2CH3
CH2CH2CH3
CH2(CH2)2CH3
CH2(CH2)3CH3
CH2(CH2)6CH3
CH2(CH2)10CH3
CH2(CH2)14CH3
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
8
8
8
8
8
8
32
55
63
72
83
82
80

Synthesis of 1,2-Diketones
495
Table 2. Synthesis of benzils in different solvents
Entry
Solvent
Time (h)
Yield (%)
1
2
3
4
CH3CH2OH
CH3OH
H2O
24
24
24
24
67
36
83
55
THF
EXPERIMENTAL
Typical procedure for the synthesis of 1,2-diketones: Benzaldehyde 1a
(1.06 g, 10 mmol) was added to water (10 mL). To the mixture were added
2e (0.5 mmol) and 10% NaOH aq (2.5 ml) under vigorous stirring. The
reaction mixture was stirred for about 30 min at refluxing temperature.
The solution was neutralized to pH ¼ 5–6 by HOAc. Then 12 mmol
FeCl3 ꢀ 6H2O were added into the solution. The solution was refluxed
for another 7.5 h. The crude 1,2-diketone was obtained by extracted
with ethyl acetate and concentrated in vaccuo. Pure 1,2-diketone was
obtained by column chromatography (silica, hexane–EtOAc ¼ 4:1) and
1
characterized by IR and H NMR spectral data. Their melting points
were compared with authentic samples.
Table 3. Synthesis of benzils in one-pot reaction
Mp (ꢁC)
Entry
Ar
Product Time (h) Yield (%)a Found Reported
1
2
3
4
5
6
7
8
Ph
3a
3b
3c
3d
3e
3f
3g
3h
3i
8
24
24
36
8
8
8
36
8
36
8
83
75
70
None
94
86
80
Trace
90
95–96
103–105 103–105
130–131 131–132
95–96
4-MeꢂC6H4
4-MeOꢂC6H4
4-OHꢂC6H4
4-ClꢂC6H4
3-BrꢂC6H4
4-BrꢂC6H4
4-NO2ꢂC6H4
3-ClꢂC6H4
3-NO2ꢂC6H4
Furan-2-yl
—
—
195–198 195–196
122–124
224–226 225–227
—
—
—
9
10
11
114–116 116–117
124–126
165–166 167–168
3j
3k
Trace
<5
—
aIsolated yields.

496
X. Jing et al.
ACKNOWLEDGMENTS
This research was supported by the National Natural Science
Foundation of China (20572091 20576111) and the Cultivation and
Construction Fund for the State Key Subject of Physical Chemistry.
REFERENCES
1. Mattay, J.; Runsink, J. Additions of 1,1-diethoxyethene to 1,2-diketones.
J. Org. Chem. 1985, 50, 2815–2818.
2. Hillis, L. R.; Ronald, R. C. Total synthesis of (ꢂ)-grahamimycin A1. J. Org.
Chem. 1985, 50, 470–473.
3. Souppe, J.; Namy, J. -L.; Kagan, H. B. Reactions of acyl anions generated from
acid chlorides and diiodosamarium. Tetrahedron Lett. 1984, 25, 2869–2872.
4. Zibuck, R.; Seebach, D. Note on the preparation of 1,2-diketones from acet-
ylenes. Helv. Chim. Acta 1988, 71, 237–240.
5. McKillop, R.; Oldenziel, O. H.; Swann, B. P.; Taylor, E. C.; Robey, R. L.
Thallium in organic synthesis, XXXIV: Oxidations of acetylenes with
thallium(III) nitrate (TTN). J. Am. Chem. Soc. 1973, 95, 1296–1303.
6. Lee, D. G.; Chang, V. S. The preparation of alpha-diones: Phase-transfer assisted
oxidation of alkynes by potassium permanganate. Synthesis 1978, 462–463.
7. (a) Anelli, P. L.; Banfi, S.; Montanari, F.; Quici, S. Oxidation of diols with
alkali hypochlorites catalyzed by oxammonium salts under two-phase con-
ditions. J. Org. Chem. 1989, 54, 2970–2972; (b) Banwell, M. G.; Bridges,
V. S.; Dupuche, J. R.; Richards, S. L.; Walter, J. M. Oxidation of vic-diols
to a-dicarbonyl compounds using the oxoammonium salt derived from
4-acetamido-TEMPO and p-toluenesulfonic acid. J. Org. Chem. 1994, 59,
6338–6343; (c) Inokuchi, J.; Matsumoto, S.; Nishiyama, T.; Torii, S. Indirect
electrooxidation of alcohols by
a double mediatory system with
[R2Nþ ¼ O]=R2N-O and [Br. or Brþ]Brꢂ redoxes. Synlett 1990, 57–58.
8. Campestrini, S.; Furia, F. D.; Modena, G. Metal catalysis in oxidation
by peroxides, part 33: Chemoselective alcohol oxidations by the anionic
molybdenum-picolinate N-oxido peroxo complex MoO5PICO. J. Org.Chem.
1990, 55, 3658–3660.
9. Iwahama, T.; Sakaguchi, S.; Nishiyama, Y.; Ishii, Y. A direct conversion of
vic-diols into 1,2-diketones with aqueous hydrogen peroxide catalyzed by
peroxotungstophosphate (PCWP). Tettrahedron Lett. 1995, 36, 1523–1526.
10. (a) Rigby, W. A new reagent for the oxiation of acyloins to diketones. J. Chem.
Soc. 1951, 793–795; (b) Clarke, H. T.; Dreger, E. E. Benzil. Org. Synth. Coll.
1941, 1, 87–89.
11. Baskaran, S.; Das, J; Chandrasekaran, S. Heterogeneous permanganate
oxidations: An improved procedure for the direct conversion of olefins to
a-diketones=a-hydroxy ketones. J. Org. Chem. 1989, 54, 5182–5184.
12. Iwamoto, K.; Hamaya, M.; Hashimoto, H.; Kimura, H.; Suzuki, Y.; Sato, M.
Benzoin reaction in water as an aqueous medium catalyzed by benzimida-
zolium salt. Tetrahedron Lett. 2006, 47, 7175–7177.