Mo(CO)6-catalyzed oxidation of furan derivatives to E- and Z-enediones by cumyl hydroperoxide

Article abstract of DOI:10.1016/S0040-4039(02)02636-9

E- and Z-Enediones are easily accessible by controlled oxidation of 2,5-disubstituted furans with Mo(CO)₆/cumyl hydroperoxide system. The use of t-butyl hydroperoxide, as oxygen donor, leads to the formation of 2H-pyran-3(6H)-one derivatives.

Full text of DOI:10.1016/S0040-4039(02)02636-9

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 835–837
Mo(CO) -Catalyzed oxidation of furan derivatives to E- and
6
Z-enediones by cumyl hydroperoxide
Antonio Massa, Maria Rosaria Acocella, Margherita De Rosa, Annunziata Soriente,
Rosaria Villano and Arrigo Scettri*
Dipartimento di Chimica, Universit a` di Salerno, 84081 Baronissi (Salerno), Italy
Received 28 October 2002; revised 19 November 2002; accepted 20 November 2002
Abstract—E- and Z-Enediones are easily accessible by controlled oxidation of 2,5-disubstituted furans with Mo(CO) /cumyl
6
hydroperoxide system. The use of t-butyl hydroperoxide, as oxygen donor, leads to the formation of 2H-pyran-3(6H)-one
derivatives. © 2003 Elsevier Science Ltd. All rights reserved.
Furan derivatives represent important synthetic sub-
strates because of their latent enedicarbonyl functional-
ity that can be easily disclosed by a variety of oxidative
of several classes of compounds, as cyclopentenone
11,12 3 13
derivatives
polyfunctional open-chain systems, variously substi-
17
(rethrolones, prostaglandins ), chiral
14
1
,2
3
15
16
photochemical,
electrochemical
and chemical
tuted furans, 3(2H)-furanones, 2(3H)-furanones,
18
methodologies. In particular, as regards the chemical
conversion of furans 1 into products 2 very satisfactory
results have been obtained by using epoxidizing agents
2,5-dihydrofurans.
Now, we wish to report a very simple procedure, based
4
5
(
m-chloroperbenzoic acid, dioxirane, magnesium
6
on the employment of Mo(CO) /cumyl hydroperoxide
6
monoperoxyphtalate,
methyltrioxorhenium/urea-
(
CHP) system as mild oxidant of 2,5-dialkyl furans of
7
hydrogen peroxide adduct ), metal oxidants (pyri-
type 1, that allows to get alternatively E- or Z-ene-
diones 2 in satisfactory yields (Scheme 2).
8
dinium chlorochromate,
cerium(IV) ammonium
9
nitrate ), or by a two step sequence involving the
previous conversion of 1 into the corresponding 2,5-
dialkoxy-2,5-dihydrofurans, followed 0by controlled
In fact, when the starting materials 1 were submitted to
treatment with CHP (1 equiv.) in CHCl solution under
3
1
hydrolysis to 2 under acidic conditions. Furthermore,
the conditions reported in Scheme 2 and Table 1
it is noteworthy that 2 can be obtained in the desired E
or Z CꢀC geometry by a careful choice of the reagents
and/or the experimental conditions (Scheme 1).
(
entries a–d), the formation of E-2 was found to take
place in a satisfactory way.
Since all the previously reported procedures involving
the use of epoxidizing agents afforded exclusively Z-
enediones 2, we supposed that, under the conditions of
Proc. A, a ready Z“E isomerization could be pro-
moted by the slightly acidic reaction medium. In fact,
when the same experiments were performed in the
The wide availability of procedures can be surely
attributed to the important synthetic value of com-
pounds 2, used as key-intermediates in the preparation
presence of anhydrous Na CO3 (1 equiv.), Proc. B,
2
products 2 could be isolated as Z geometrical isomers
(
entries e–h, Table 1).
Furthermore, it has to be noted that when t-butyl
hydroperoxide (TBHP) was used in substitution of
CHP, very complex mixtures of products were obtained
in consequence of the unexpected high reactivity of
compounds 2 under the standard conditions. However,
under more controlled conditions involving treatment
Scheme 1.
*
Corresponding author. Tel.: +39-89-965-374; fax: +39-89-965-296;
e-mail: scettri@unisa.it
0
040-4039/03/$ - see front matter © 2003 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)02636-9

8
36
A. Massa et al. / Tetrahedron Letters 44 (2003) 835–837
Scheme 2.
Table 1. Mo(CO) -catalyzed oxidation of 2,5-dialkyl furans 1 with CHP
6
Entry
R
Reac. time (h)
Procedure
Product
Yield (%)a
a
b
c
d
e
f
g
h
n-C H
20
16
20
24
20
20
24
12
A
A
A
A
B
B
B
B
E-2a
E-2b
E-2c
E-2d
Z-2a
Z-2b
Z-2c
Z-2d
65
67
63
93
64
61
63
53
4
9
n-C H
7
15
19
n-C H
9
-H
n-C H
4
9
n-C H
7
15
n-C H1
9
9
-H
a
All the yields refer to isolated chromatographically pure compounds whose structures were confirmed by IR and 1H NMR data and by
comparison with authentic samples prepared through known procedures.
4
,8
with TBHP (1 equiv.), in CHCl solution at 40°C, in
the presence of a very reduced amount of Mo(CO)6
in order to get the complete conversion of the starting
material (entry d, Table 2) the corresponding products
E-2b and 4b were obtained in 45 and 55% yield,
respectively.
3
(
0.01 equiv.), the formation of E-2 enediones was again
found to occur in appreciable yields (Table 2) although
incomplete conversion was required in order to mini-
mize the formation of the additional reaction products
A set of experiments has then allowed to disclose an
unprecedented reactivity both of Z- and E-2 and fur-
thermore, to obtain useful information on the reaction
pathway leading to compounds 4. In fact, irrespective
4
(Scheme 3).
It is noteworthy that, when 3 equiv. of TBHP were used
Table 2. Mo(CO) -catalyzed oxidation of dialkyl furans 1 with TBHP
6
a
b
Entry
R
Reac. time (h)
Conv. (%)
E-2 Yield (%)
4 Yield(%)
a
b
c
n-C H
24
24
32
8
80
82
83
52
50
52
10
4
4
9
n-C H
7
15
19
15
n-C H
10
9
c
b
b
d
n-C H
100
45
55
7
a
All the yields refer to isolated chromatographically pure compounds whose structures were confirmed by IR and 1H NMR data and by
8
,19
comparison with authentic samples obtained by previously reported procedures.
b
c
1
In this entry the yields were calculated by H NMR analysis on the crude reaction mixture.
In this entry 3 equiv. of TBHP were used.
Scheme 3.

A. Massa et al. / Tetrahedron Letters 44 (2003) 835–837
837
the time reported in Table 1. Then, a 0.1N aqueous
solution of Na S O (15 ml) was added and the mixture
2
2
3
was stirred at rt for 1 h. The absence of unreacted
hydroperoxide was established with acidified starch–
2
0
iodide test paper, according to Sharpless’ report.
Then, diethyl ether (50 ml) was added and the organic
phase was washed with brine (3×10 ml) until neutrality.
Scheme 4.
After drying over anhydrous Na SO , the solvent was
2 4
removed under a reduced pressure and the resulting
crude product 2 was purified by silica gel column
chromatography by elution with n-hexane–diethyl ether
mixtures.
Table 3. Mo(CO) -catalyzed oxidation of 2 to 5 with
6
TBHP
a
Entry
Substrate
Reac. time
h)
Conversion
(%)
5 Yield (%)
(
References
a
b
c
Z-2b
E-2b
E-2c
E-2d
62
60
64
64
91
88
87
90
58
57
59
63
1
2
. Feringa, B. L. Recl. Trav. Chim. Pays-Bas 1987, 106, 469.
. Graziano, M. L.; Iesce, M. R.; Carli, B.; Scarpati, R.
Synthesis 1983, 125.
3. Shono, T.; Matsumura, Y.; Hamaguchi, H.; Nakamura,
K. Chem Lett. 1976, 1249.
4. Kobayashi, Y.; Katsuno, H.; Sato, F. Chem Lett. 1983,
d
a
All the yields refer to isolated chromatographically pure compounds
and are calculated on the starting materials. Structural determina-
tion is based on IR, H and C NMR and by comparison with
authentic samples obtained by a previously reported procedure. In
all entries mixed peroxides of type 4 were obtained as less abundant
products (8–10% yields).
1
13
1
9
1771.
5
. Adger, B.; Barrett, C.; Brennan, J.; McKervey, M. A.;
Murray, R. W. J. Chem. Soc., Chem. Commun. 1991,
1553.
6
7
8
9
. Dominguer, C.; Csaky, A. G.; Plumet, J. Tetrahedron
Lett. 1990, 31, 7669.
. Finlay, J.; McKervey, M. A.; Nimal-Gunaratne, H. Q.
Tetrahedron Lett. 1998, 39, 5651.
. Piancatelli, G.; Scettri, A.; D’Auria, M. Tetrahedron
of the CꢀC bond geometry, enediones 2 were smoothly
converted into the peroxypyranone derivatives 5 under
the usual oxidative conditions [TBHP (3 equiv.),
Mo(CO) (0.01 equiv.) in CHCl solution at rt for 72 h]
6
3
1980, 36, 661.
(
Scheme 4, Table 3).
. Lepage, L.; Lepage, Y. Synthesis 1983, 1018.
1
1
0. Hirsch, J. A. J. Heterocyclic Chem. 1972, 9, 523.
1. Shinoara, T.; Kurata, T.; Kitano, Y.; Matsumoto, K.;
Takahashi, I.; Hosoi, S.; Ota, T.; Hatanaka, M. Synlett
Although the mechanistic aspects have not been fully
clarified, the involvement of intermediates 3b and 4b in
the oxidative conversion of Z-2b (chosen as representa-
tive substrate) into 5b has been supported by the
achievement of the synthetic sequence reported in
Scheme 5.
2002, 8, 1245.
1
2. Kitano, Y.; Minami, S.; Morita, T.; Matsumoto, K.;
Hatanaka, M. Synthesis 2002, 6, 739.
1
1
1
3. Floyd, M. B. J. Org. Chem. 1978, 43, 1641.
4. Raczko, J. Polish J. Chem. 1999, 73, 77.
5. Antonioletti, R.; D’Auria, M.; Piancatelli, G. J. Chem.
Soc., Perkin 1 1981, 2398.
In conclusion, both E- and Z-enediones are readily
accessible by a simple and convenient procedure and,
furthermore, products 2 prove to be useful intermedi-
ates in the preparation of furan and 2H-pyran-3(6H)-
one derivatives.
1
6. Antonioletti, R.; Bonadies, F.; Scettri, A. Tetrahedron
Lett. 1987, 28, 2297.
7. D’Auria, M.; De Mico, A.; Piancatelli, G.; Scettri, A.
Tetrahedron Lett. 1982, 38, 1661.
1
Typical procedure for the oxidation of 1 to enediones 2
by CHP
18. D’Annibale, A.; Scettri, A. Tetrahedron Lett. 1995, 36,
4659.
19. Antonioletti, R.; Arista, L.; Bonadies, F.; Locati, L.;
A mixture of 1 (2 mmol), Mo(CO) (0.2 mmol), CHP (2
Scettri, A. Tetrahedron Lett. 1993, 34, 7089.
20. Sharpless, K. B. Aldrichim. Acta 1979, 12, 63 (see Ref.
6
mmol), anhydrous Na CO (2 mmol) (required for the
2
3
synthesis of Z-2) CHCl (4 ml) was stirred at 50°C for
80).
3
Scheme 5. Reagents and conditions: (a) TBHP (3 equiv.), Mo(CO) (0.01 equiv.), CHCl , 24 h, rt.
6
3