Ytterbium triflate catalyzed heterocyclization of 1,2-phenylenediamines and alkyl oxalates under solvent-free conditions via phillips reaction: A facile synthesis of quinoxaline-2,3-diones derivatives

Article abstract of DOI:10.1081/SCC-120030683

Ytterbium triflate are found to catalyze efficiently the Phillips-type heterocyclization reactions of 1,2-phenylenediamine and alkyl oxalate under solvent-free and mild conditions to afford the corresponding quinoxaline-2,3-dione derivatives in high yields. The catalyst could be recovered almost quantitatively from the aqueous layer after the reaction was completed and it could be reused in subsequent reaction without decrease in activity.

Full text of DOI:10.1081/SCC-120030683

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Ytterbium Triflate Catalyzed Heterocyclization of
1,2‐Phenylenediamines and Alkyl Oxalates Under
Solvent‐Free Conditions via Phillips Reaction:
A Facile Synthesis of Quinoxaline‐2,3‐diones
Derivatives
a
a
a
b
Limin Wang , Jijun Liu , He Tian & Changtao Qian
a
Institute of Fine Chemicals, East China University of Science and Technology, 130
Meilong Lu, Shanghai, 200237, P.R. China
b
Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, Shanghai, P.R. China
Version of record first published: 21 Aug 2006.
To cite this article: Limin Wang, Jijun Liu, He Tian & Changtao Qian (2004): Ytterbium Triflate Catalyzed
Heterocyclization of 1,2‐Phenylenediamines and Alkyl Oxalates Under Solvent‐Free Conditions via Phillips Reaction: A
Facile Synthesis of Quinoxaline‐2,3‐diones Derivatives, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 34:8, 1349-1357
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w
SYNTHETIC COMMUNICATIONS
Vol. 34, No. 8, pp. 1349–1357, 2004
Ytterbium Triflate Catalyzed
Heterocyclization of 1,2-Phenylenediamines
and Alkyl Oxalates Under Solvent-Free
Conditions via Phillips Reaction: A Facile
Synthesis of Quinoxaline-2,3-diones
Derivatives
1
,
1
1
2
Limin Wang, * Jijun Liu, He Tian, and Changtao Qian
1
Institute of Fine Chemicals, East China University of Science and
Technology, Shanghai, P.R. China
2
Laboratory of Organometallic Chemistry, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences, Shanghai, P.R. China
ABSTRACT
Ytterbium triflate are found to catalyze efficiently the Phillips-type
heterocyclization reactions of 1,2-phenylenediamine and alkyl oxalate
under solvent-free and mild conditions to afford the corresponding
quinoxaline-2,3-dione derivatives in high yields. The catalyst could be
recovered almost quantitatively from the aqueous layer after the reaction
*
Correspondence: Limin Wang, Institute of Fine Chemicals, East China University of
Science and Technology, 130 Meilong Lu, Shanghai 200237, P.R. China; Fax: 86-21-
6
4252288, 64252758; E-mail: wanglimin@ecust.edu.cn/wcathy@china.com.
1
349
DOI: 10.1081/SCC-120030683
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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Wang et al.
was completed and it could be reused in subsequent reaction without
decrease in activity.
Key Words: Quinoxaline-2,3-diones; Yb(OTf) ; Solvent-free synthesis;
3
Phillips reaction.
INTRODUCTION
The quinoxaline skeleton, when selectively functionalized, is a building
block for the preparation of numerous amino acids and substances with
[
1]
pronounced biological activities.
reported that certain quinoxaline-2,3-diones are structural units in many
Recently, several publications have
[
2]
antagonists for the excitatory system. The most common synthetic method
[3]
of quinoxaline-2,3-diones are based on the general Phillips reaction, which
[4]
involves oxalate derivatives with 1,2-phenylenediamines and analogs. The
ring closure of 1,2-phenylenediamine with oxalate derivatives used to form
the six-member paradiazine ring of a quinoxaline-2,3-dione, is usually the
last and crucial step. Normally, this step is carried out using the method of
Phillips under lengthy and harsh conditions. The Phillips heterocyclization
[5]
reaction is carried out slowly at the catalysis of strong Lewis acid or at
[4]
elevated or reflux (diether oxalate has a b.p. 182–1868C ) temperatures
that are not amenable to molecules bearing sensitive functional groups.
[6]
Sometimes a solvent is also used. However, it suffers from many disadvan-
[7]
tages, either high temperatures or protic Lewis acids. Stone-Elander et al.
described the successful use of solid supports and/or solvent-free media with
[8]
focused microwave fields to achieve heterocyclization. Other authors
described the rotary evaporation of 1,2-diamino aromatic compounds in
diethyl oxalate at 50–808C and 20 mbar leads to formation of quinoxaline-
2,3-diones. In their modified procedure, no other solvents and no catalysts
have been employed. Therefore, the development of simple and novel
reagents, which are more efficient and convenient procedures with improved
yield, is needed.
Recently, lanthanide triflates has attracted the interest of synthetic
organic chemists because they have emerged as potential and water-tolerant
Lewis acids imparting high regio- and chemoselectivity in various chemical
transformation. The reaction can be conveniently carried out under mild con-
ditions either in aqueous and in nonaqueous or in solvent-free conditions, and
[9]
the catalyst can be recovered and recycled in subsequent reactions. The
unique catalytic features of lanthanide triflates prompted us to investigate
the use of this catalyst for Phillips reaction. In continuting our research into
[10]
lanthanide triflates catalyzed organic synthetic reactions,
we describe

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Yb(OTf) Catalyzed Heterocyclization
3
1351
a remarkable, efficient and high yielding protocol for the preparation of
through Phillips reaction of 1,2-phenylenediamines and alkyl oxalate deriva-
tives in solvent-free conditions employing ytterbium triflates as efficient and
mild catalyst.
RESULT AND DISCUSSION
At the outset, we have examined the reaction of 1,2-phenylenediamine
1a) with diethyl oxalate (2a) in the presence of ytterbium triflate and have
(
tested a variety of reaction conditions (Sch. 1). The modification Phillips
reaction under solvent-free proceeded smoothly to afford the corresponding
quinoxaline-2,3-dione (3a) in high yield (89%) using a catalytic amount of
ytterbium triflate (0.05 equiv.) at 808C for 1 hr (Sch. 2). To optimize the
cyclization reaction, the reaction results are summarized in Table 1. It
shows that Yb(OTf) did effectively catalyze the cyclocondensation reac-
3
tion. Use of just 5 mol% of Yb(OTf) is sufficient to push the reaction
3
forward, and Yb(OTf) could be reused three times without showing any
3
loss of activity (entry 8). Typically, eight or nine molecules of water are
contained in the ytterbium triflate after removal of water at room tempera-
ture. Anhydrous ytterbium triflate are obtained after drying at elevated
[9]
temperature under high vacuum. We had already found that the catalytic
activity of anhydrous Yb(OTf) was higher than that of hydrous Yb(OTf) in
this reaction. When the reaction were attempted using H SO (5 M) in
3
3
2
4
solvent-free conditions, only trace amounts of 3a were obtained at 808C
for 1 hr. The reaction did not occur without any Yb(OTf) even for 24 hr.
3
Experiments with conventional reflux conditions in e.g. DMSO or DMF indi-
cated that reflux 6 hr in an oil-bath afforded the desired products.The reactions
in DMSO and DMF were very slow, and gave low yields, such as DMSO
(36%), DMF (41%). It is apparent that reactions under solvent-free conditions
plays an important role for attaining good yield, and the reaction time was
Scheme 1.

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1
352
Wang et al.
Scheme 2.
shortened from 6 to 1 hr. On the other hand, the reaction temperature was
decreased from 1808C to 808C.
In all cases, several 1,2-phenylenediamine derivatives reacted well with
alkyl oxalate derivatives to give the respective quinoxaline-2,3-dione deriva-
tives in good yields under optimized reaction condition in the presence of
ytterbium triflate (Table 2). The ester groups of oxalate had minor effect on
the yields. The oxalate with ethyl group is more reactive than those with iso-
propyl and n-butyl groups (Table 2, entries 1, 2, 3). For instance, treatment of
the 1,2-phenylenediamine with the di-n-butyl oxalate gave the corresponding
compound 3a in 87% yield (entry 3). Most importantly, 1,2-phenylenedi-
amines carrying either electron-withdrawing substituents such as nitro or
chloro groups on the aromatic ring or electron-donating substituents such as
methyl or amino groups on the aromatic ring all reacted very well, giving
Table 1. Reaction of 1,2-phenylenediamine and diethyl oxalate under
different reaction conditions.
Amount of
catalyst (mol%)
a
b
Entry
Solvent
Catalyst
Yield (%)
c
1
2
3
4
5
6
7
8
None
None
DMSO
DMF
None
5
5
No reaction
Trace
H
2
SO
Yb(OTf)
Yb(OTf)3
4
3
5
36
41
5
d
None
Yb(OTf)
Yb(OTf)
3
3
5
89
89
None
None
None
10
2.5
5
Yb(OTf)3
86
e
3
Yb(OTf)
88, 86, 85
a
Refluxed for 6 hr.
Isolated yield.
b
c
8
08C for 24 hr.
08C for 1 hr.
d
8
Catalyst was reused three times.
e

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Yb(OTf) Catalyzed Heterocyclization
3
1353
3
Table 2. Yb(OTf) catalyzed synthesis of different quinoxaline-2,3-
diones under the solventless conditions.
a
Entry
R1
R2
X
Product
Yield (%)
1
2
3
4
5
6
7
8
H
C
i-Pr
2
H
5
NH
NH
2
2
3a
3a
3a
3b
3c
3d
3e
3f
89
81
87
82
79
83
80
78
H
H
n-C H
4
NH2
9
CH
3
C
C
2
H
H
5
5
5
5
5
NH
NH
2
2
NH
Cl
2
2
C H
2
NH2
NH2
OH
NO2
H
C H
2
2
C H
a
Isolated yield.
good yields. Further we examined the reactivity of ortho-aminophenol and
diethyl oxalate in the presence of ytterbium triflate, and the reaction proceeded
smoothly under the same conditions to afford the corresponding compound 3f
in moderate yield (78%), which showed that ytterbium triflate effectively cata-
lyzed this reaction indeed.
In summary, we have demonstrated that Yb(OTf) is a superior Lewis
3
acid for the Phillips reaction of 1,2-phenylenediamine derivatives with
alkyl oxalate derivatives. The catalyst was recovered from the aqueous
layer during work-up and recycled in subsequent reaction without loss of
activity. The method avoids prolonged heating at high temperature with
protic acids as well as Lewis acids, for instance, sulfuric acid. The yields
[7]
of the Phillips reaction can be increased from 19–46% to 79–89% while
[8]
the reaction time was shortened from 4–24 hr to 1 hr. The procedure
has the advantages of mild reaction condition, high yields of products,
short reaction times, low reaction temperature, small quantity of catalyst,
environmentally friendly, operational and experimental simplicity which
makes this method a useful and attractive strategy for the synthesis of
quinoxaline-2,3-diones derivatives.
EXPERIMENTAL SECTION
General
1
Melting points were determined on a Kofler hot stage. H NMR spectra
were recorded at 500 MHz in DMSO using TMS as internal standard. IR

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1
354
Wang et al.
spectra were obtained as KBr plates on FTS-185. Mass spectra were deter-
mined on a Finigan 8230 mass spectrometer.
Yb(OTf) Catalyzed Synthesis of Different Quinoxaline-2,3-
3
diones Under the Solventless Conditions
1,2-Phenylenediamine derivatives (1 mmol), oxalate derivatives
1.5 mmol), and Yb(OTf) (0.05 mmol, 5 mol%) were mixed. The mixture
(
3
was stirred for 1 hr at 808C. Then water was added and the product was
extracted with ethyl acetate. After the organic layer was dried (MgSO ) and
evaporated, the residue was recrystallized by ethanol to products 3. The cata-
lyst remaining in the aqueous phase can be recovered by removing the water
4
through heating and then dying under vacuum at 1008C for 2 hr.
1
1,2,3,4-Tetrahydroquinoxaline-2,3-dione (3a). M.p. .3008C;
H
NMR (DMSO-d ): d ¼ 11.92 (s, 2H, NH), 7.07–7.14 (m, 4H, Ar), IR
6
2
1
þ
(
KBr): 2930, 2850, 2910, 1690 cm ; GC/MS: m/z (%) ¼ 162.1 (M ,
1
1
00), 163.1 (M þ 1, 8); HRMS calcd for C H N O : 162.0429. Found:
8
6 2 2
62.0432.
-Methyl-1,2,3,4-tetrahydroquinoxaline-2,3-dione (3b). M.p. .3008C;
6
1
H NMR (DMSO-d ): d ¼ 11.84 (s, 2H, NH), 7.02 (d, 1H, J ¼ 8.0 Hz, Ar),
6
6
.90 (d, 2H, J ¼ 11.2 Hz, Ar), 2.26 (s, 3H, CH ).
3
6
-Amino-1,2,3,4-tetrahydroquinoxaline-2,3-dione (3c). M.p. .3008C;
1
H NMR (DMSO-d ): d ¼ 11.86 (s, br, 2H, NH), 6.82 (d, 1H, J ¼ 9.11 Hz,
6
Ar), 6.34 (d, 2H, J ¼ 6.04 Hz, Ar), 5.11 (s, 2H, NH ).
2
6
-Chloro-1,2,3,4-tetrahydroquinoxaline-2,3-dione (3d). M.p. .2908C;
1
H NMR (DMSO-d ): d ¼ 12.07 (s, 2H, NH), 7.20 (d, 2H, J ¼ 12.89 Hz, Ar),
6
7
.14 (d, 1H, J ¼ 8.30 Hz, Ar).
6
-Nitro-1,2,3,4-tetrahydroquinoxaline-2,3-dione (3e). M.p. .3008C;
1
H NMR (DMSO-d ): d ¼ 12.25 (s, 2H, NH), 7.94 (d, 2H, J ¼ 12.91 Hz,
6
þ
Ar), 7.24 (d, 1H, J ¼ 8.43 Hz, Ar); GC/MS: m/z (%) ¼ 207.1 (M , 100),
2
08.1 (M þ 1, 9).
1
1
,2,3,4-Tetrahydroquinoxazine-2,3-dione (3f). M.p. .3008C; H NMR
(
(
DMSO-d ): d ¼ 11.82 (s, H, NH), 7.02–7.16 (m, 4H, Ar), GC/MS: m/z
6
þ
%) ¼ 163.0 (M , 68), 164.0 (M þ 1, 7), 135 (100).
ACKNOWLEDGMENT
We thank the National Nature Science Foundation of China and the
Science Foundation of East China University of Science and Technology
for their financial support.

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Received in Japan July 25, 2003

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