Simple, efficient, and stereoselective oxidation of triphenylfurans to cis-but-2-ene-1,4-diones

Article abstract of DOI:10.1080/00397910601055065

Triphenylfurans are stereoselctively oxidized to cis-but-2-ene-1,4-diones, suitable precursors of 3(2H)-furanones, in very good yields using ammonium nitrate or potassium nitrate in 80% aqueous acetic acid. Copyright Taylor & Francis Group, LLC.

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Simple, Efficient, and Stereoselective
Oxidation of Triphenylfurans to
cis‐But‐2‐ene‐1,4‐diones
John P. Rappai a , Sreedharan Prathapan a , Manthitta V. Vishnu Unni a &
Perupparampil A. Unnikrishnan a
a Department of Applied Chemistry , Cochin University of Science and
Technology , Kochi, Kerala, India
Published online: 05 Mar 2007.
To cite this article: John P. Rappai , Sreedharan Prathapan , Manthitta V. Vishnu Unni & Perupparampil
A. Unnikrishnan (2007) Simple, Efficient, and Stereoselective Oxidation of Triphenylfurans to
cis‐But‐2‐ene‐1,4‐diones, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 37:4, 569-572, DOI: 10.1080/00397910601055065
To link to this article: http://dx.doi.org/10.1080/00397910601055065
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Synthetic Communicationsw, 37: 569–572, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910601055065
Simple, Efficient, and Stereoselective
Oxidation of Triphenylfurans
to cis-But-2-ene-1,4-diones
John P. Rappai, Sreedharan Prathapan,
Manthitta V. Vishnu Unni, and
Perupparampil A. Unnikrishnan
Department of Applied Chemistry, Cochin University of Science
and Technology, Kochi, Kerala, India
Abstract: Triphenylfurans are stereoselctively oxidized to cis-but-2-ene-1,4-diones,
suitable precursors of 3(2H)-furanones, in very good yields using ammonium nitrate
or potassium nitrate in 80% aqueous acetic acid.
Keywords: cis-but-2-ene-1,4-diones, 3(2H)-furanones, stereoselective oxidation,
triphenylfurans
Oxidation of suitably substituted furans to cis-but-2-ene-1,4-diones has
been effected by a variety of reagents including nitric acid, chromic acid–
acetic acid mixture,[1,2] lead tetraacetate,[3,4] hydrogen peroxide,[5,6]
ozone,[2,7] photooxidation,[2,8–11] halogen,[3,12] phosphorous pentahalides,[13]
cerium(IV) ammonium nitrate (CAN),[14] and dimethyldioxirane.[15] It has
also been reported that the reaction of benzoin with lithium nitrate in acetic
anhydride gave benzil, although in low yields.[16] Later, Klein found that
ammonium nitrate in acetic acid acts as a mild oxidizing agent and can be
used to oxidize a-hydroxyketones to diketones in near quantitative yields.[17]
Received July 7, 2006
Address correspondence to John P. Rappai, Department of Applied Chemistry,
Cochin University of Science and Technology, Kochi 682 022, Kerala, India.
E-mail: jones@cusat.ac.in
569

570
J. P. Rappai et al.
Table 1. Oxidative cleavage of furan derivatives
Yield
(%)
Entry
Substrate
X
R
Product
1
2
1a
1b
1c
1d
1e
1f
1g
3
Br
Br
Br
Br
Br
Br
Cl
–
H
2a
2b
2c
2d
2e
2f
2g
4
74a
73a
73a
75a
74a
72a
78a
72a
70a
80b
76b
Me
OMe
Cl
3
4
5
Br
C6H11
H
6
7
8
–
9
5
–
–
6
10
11
1a
3
Br
–
H
2a
4
–
a
Note. The reaction was conducted using ammonium nitrate in
aqueous acetic acid (80%, v/v) at reflux for 90 min with occasional
b
stirring; potassium nitrate in aqueous acetic acid (80%, v/v) at
reflux for 30 min.
RESULTS AND DISCUSSION
The furans were prepared according to the literature procedures. The oxidation
of 3-halofurans 1a–g using a stoichiometric amount of ammonium nitrate in
aqueous acetic acid (80%, v/v) produced cis-1-aryl-2-halo-3,4-diphenylbut-2-
ene-1,4-diones 2a–g in high yields (Table 1, Scheme 1).
We also found that the oxidative cleavage of 2,3,5-triphenylfuran 3 under
the same oxidative condition gives the corresponding cis-but-2-ene-1,4-dione
4 in near quantitative yields (Scheme 2), whereas 2,5-diphenylfuran 5
gives the corresponding trans-but-2-ene-1,4-dione 6 in good yields
(Scheme 3).The formation of trans-enedione in this case may be due to the
acid-catalyzed isomerization of the initially formed cis-enedione under the
Scheme 1.

Stereoselective Oxidation of Triphenylfurans to cis-But-2-ene-1,4-diones
571
Scheme 2.
reaction conditions.[18] The exclusive formation of the cis-enediones shows
that in all these instances the reaction is consistently stereoselective.
Interestingly, KNO3 was also found to be an efficient oxidizing agent for
the oxidation of furans. cis-But-2-ene-1,4-diones were formed in better yields
when KNO3 was used as the oxidizing agent than when obtained with
ammonium nitrate (Table 1, entries 10 and 11).
In summary, we have developed a simple, efficient, and ecofriendly route
for the oxidation of triphenylfurans to the corresponding cis-but-2-ene-1,4-
diones, suitable precursors of 3(2H)-furanones, in high yields. Studies on
the oxidation reactions of furans using transition-metal nitrates are in progress.
EXPERIMENTAL
General Procedure for the Synthesis of cis-But-2-ene-1,4-diones
A mixture of furan (10 mmol), aqueous acetic acid (80%, v/v) (10 mL), and
ammonium nitrate (1.3 g, 12.5 mmol) was heated at reflux for 90 min. The
Scheme 3.

572
J. P. Rappai et al.
reaction mixture was cooled, diluted with cold water, and filtered. The crude
product was purified by recrystallization from methanol. The cis-but-2-ene-
1,4-diones were characterized by comparing their spectral and analytical
data with those of authentic samples prepared by reported procedures.[19,20]
ACKNOWLEDGMENT
This work was supported by Department of Science and Technology, Govern-
ment of India, in the form of Research Grant No. SP/S1/G-23/2000. J. P. R.
acknowledges Council for Scientific and Industrial Research, India, for
financial assistance in the form of a research fellowship. M. V. V. U. acknowl-
edges the University Grants Commission, India, for financial assistance.
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