SCHEME 1
F a cile Micr ow a ve-Med ia ted
Tr a n sfor m a tion s of 2-Bu ten e-1,4-d ion es a n d
2-Bu tyn e-1,4-d ion es to F u r a n Der iva tives
H. Surya Prakash Rao* and S. J othilingam
Department of Chemistry, Pondicherry University,
Pondicherry 605 014, India
TABLE 1. Micr ow a ve-Med ia ted Red u ction -
Deh yd r a tive Cycliza tion of 2-En e-1,4-d ion es/
2-Yn e-1,4-d ion es to F u r a n Der iva tives
hspr@satyam.net.in
Received February 7, 2003
sl. no.
dione
furan
time (min)
Power (W)
yield (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
1
2
3
4
5
6
7
19
20
21
22
23
24
8a
1.0
3.0
2.0
5.0
5.0
5.0
5.0
4.0
4.0
4.0
5.0
5.0
5.0
400
400
200
200
200
400
200
155
155
155
200
200
200
95
96
Abstr a ct: Several di- and triarylfuran derivatives were
prepared in high yields from but-2-ene-1,4-diones/but-2-yne-
1,4-diones using formic acid in the presence of a catalytic
amount of palladium on carbon and in poly(ethylene glycol)-
200 medium in a one-pot operation under microwave ir-
radiation (1-5 min).
9b
10b
11a
12a
13
14c
8
91
96d
96d
96
84d
93
9
92
The most widely used approach to furan synthesis is
the Paal-Knorr method in which 1,4-dicarbonyl com-
pounds are converted to furan derivatives via acid-
mediated dehydrative cyclization.1 In this century-old
reaction, the 1,4-dicarbonyl compounds provide all the
carbons as well as one oxygen necessary for the ring
closure to the furan ring. For example, 2,5-diphenylfuran,
the heterocycle relevant to the present study, has been
prepared from 1,4-diphenylbutane-1,4-dione under de-
hydrative conditions by refluxing in toluene containing
a catalytic amount of p-TSOH,2 ZnCl2 in acetic anhy-
dride,3 or polyphosphoric acid.4 Even though the reaction
is simple to perform, the limitation is the availability of
suitably substituted 1,4-diketones. Only recently have a
few good methods been developed for the synthesis of the
substrate 1,4-diketones,5 and there is still enormous
scope for improvement, particularly with regard to condi-
tions, efficiency, and applicability to a wider range of
substrates.
The 1,4-diketones for the furan synthesis can be made
by the hydrogenation of the corresponding enediones. We
envisaged that the two steps, viz. reduction of the double
bond and subsequent cyclization, could be combined in a
one-pot procedure by employing a reagent that would
effect both conversions. Previously, this concept was
explored by treating 2-ene-1,4-diones with Lewis acids,
tin(II)chloride,6 diphosphorus tetraiodide (P2I4),7 or tri-
10
11
12
13
93
89d
88d
90d
Reference 11. Reference 16. c Reference 8. Concentrated
H2SO4 (5 mol %) was used.
a
b
d
ethyl phosphite8 to furnish substituted furan derivatives.
The main disadvantages of the above procedures were
the requirement of stringent conditions, long reaction
times, and lack of applicability to 2-yne-1,4-diones. We
report here a facile, high-yielding, one-flask preparation
of furan derivatives from 2-ene-1,4-diones and 2-yne-1,4-
diones using formic acid in the presence of a catalytic
amount of palladium on carbon (5%). The rationale is that
formic acid decomposes at elevated temperature to
hydrogen and carbon dioxide and the hydrogen generated
can be used for metal-mediated hydrogenation of double
or triple bonds. Formic acid also serves as a catalyst for
the dehydrative cyclization of the 1,4-diketones to furan
derivatives. Thus, it was expected that 2-ene or 2-yne
1,4-diketones could be transformed to furan derivatives
in a one-pot operation. Recently, we reported the micro-
wave-mediated synthesis of 2,5-di- and 1,2,5-trisubsti-
tuted pyrrole derivatives from 2-butene-1,4-diones using
ammonium formate or alkylammonium formate in the
presence of palladium on carbon.9
When a two-phase reaction mixture of (E)-1,4-diphenyl-
2-butene-1,4-dione 1, formic acid, and catalytic palladium
on carbon (5%) in poly(ethylene glycol)-200 (PEG-200)
was exposed to microwaves in a domestic microwave oven
at 400 W, 2,5-diphenylfuran 8 was obtained in 95% yield
in 2 min (Scheme 1 and Table 1). In this transformation,
formic acid acted both as a source of hydrogen and as an
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1 1999, 2849. (b) Hou, X. L.; Cheung, H. Y.; Hon, T. U.; Kwan, P. L.;
Lo, T. H.; Tong, S. Y.; Wong, H. N. C. Tetrahedron 1998, 54, 1955. (c)
Benassi, R. In Comprehensive Heterocyclic Chemistry; Katrizky, A. R.,
Rees, C. W., Scriven, E. F., Eds.; Pergamon: New York, 1996; Vol. 2,
p 259. (d) Dean, F. M.; Sargent, M. V. In Comprehensive Heterocyclic
Chemistry; Katrizky, A. R., Rees, C. V., Eds.; Pergamon: New York,
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A. J . Org. Chem. 1963, 28, 148.
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(7) Demirdji, S. H.; J addadin, M. J .; Issidorides, C. H. J . Heterocycl.
Chem. 1985, 22, 495.
(4) Nowlin, G. J . Am. Chem. Soc. 1950, 72, 5754.
(5) (a) Mackay, D.; Neeland, E. G.; Taylor, N. J . J . Org. Chem. 1986,
51, 2351. (b) Hegedus, L. S.; Parry, R. J . J . Org. Chem. 1985, 50, 4955.
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10.1021/jo0341766 CCC: $25.00 © 2003 American Chemical Society
Published on Web 05/17/2003
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J . Org. Chem. 2003, 68, 5392-5394