An efficient one pot synthesis of bicyclic dienones

Article abstract of DOI:10.1039/a902012h

Bicyclic dienones 4 are prepared in a one pot process from the reaction of 2-(acetoxymethyl)cyclohex-2-enone 1 with 1,3-dicarbonyl compounds 2 in the presence of K₂CO₃ in refluxing absolute ethanol.

Full text of DOI:10.1039/a902012h

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510 J. CHEM. RESEARCH (S), 1999
J. Chem. Research (S),
1999, 510^511y
An Efficient One Pot Synthesis of Bicyclic
Dienones
Farhat Rezgui and Mohamed Moncef El Ga|ed*
Laboratoire de Chimie Organique, Faculte des Sciences de Tunis Campus Universitaire, 1060
Tunis, Tunisia
Bicyclic dienones 4 are prepared in a one pot process from the reaction of 2-(acetoxymethyl)cyclohex-2-enone 1
with 1,3-dicarbonyl compounds 2 in the presence of K2CO3 in refluxing absolute ethanol.
3
Synthetic methods for dienones 4 are fairly sparse.1 We
2 h. The solvent was evaporated in vacuo and the reaction mixture
was partitioned between water (25 ml) and diethyl ether (50 ml).
have recently reported4 that cyclization of intermediates
Aqueous 2M HCl (5 ml) was added to dissolve salts and the mixture
3, obtained from the reaction of 2-(acetoxymethyl)cyclo-
was extracted with diethyl ether (3 Â 20 ml). The ether extracts were
hex-2-enone 15;6 with 1,3-dicarbonyl compounds 2 in the
dried over MgSO4 and concentrated in vacuo. The crude product
presence of Et3N, a¡orded compounds 4 (Scheme 1).
The overall yield of this Robinson annulation,7 e¡ected
in a two-step sequence, is ca. 20^40%.
As an improvement to this method, we report herein a
direct access to dienones 4 in satisfactory yields.
was puri¢ed by column chromatography [1 : 4 then 4 : 1 diethyl
ether^light petroleum (bp 40^60 ꢀC).
Dienone 4a yellow oil; IR (CHCl3): 1659, 1630, 1589 cm
1
;
dH(300 MHz, CDCl3): 6.10^5.93 (m, 1H), 5.75 (s, 1H), 2.65 (t,
2H, J ˆ 7 Hz), 2.50^2.45 (m, 4H) 2.29^2.27 (m, 2H), 1.85^1.76
(m, 2H); dC (75 MHz, CDCl3): 199.3, 155.9, 131.8, 131.7, 123.1, 37.3,
‡
30.8, 29.4, 25.8, 22.0; MS: m/z 148 (M , 69), 133 (12), 120 (43), 105
2-(Acetoxymethyl)cyclohex-2-enone
1 reacts with 1,3-
dicarbonyl compounds 29 in the presence of a large excess
(4 equiv.) of anhydrous K2CO3 in re£uxing absolute ethanol
by an SN2 type reaction to give products 3. These
intermediates generate, in situ, via cleavage followed by
cyclization, the target bicyclic dienones 4 in 43^58% overall
yield (Scheme 1).
(37), 91 (100), 77 (22), 65 (20), 51 (21) (Found: C, 81.2; H, 8.1.
C
10H12O requires C, 81.08; H, 8.11%).
1
Dienone 4b yellow oil; IR (CHCl3): 1659, 1630, 1591 cm
;
dH(60 MHz, CDCl3): 6.17^5.90 (m, 1H), 5.67 (s, 1H), 2.77^2.10
(m, 7H), 2.01^1.54 (m, 2H), 1.23^1.04 (m, 3H); dC (75 MHz, CDCl3):
202.0, 155.0, 131.8, 131.7, 122.2, 41.0, 37.6, 30.4, 25.7, 22.0, 15.4; MS:
‡
m/z 162 (M , 100), 147 (21), 134 (74), 119 (51), 105 (22), 91 (53)
(Found: C, 81.4; H, 8.6. C10H14O requires C, 81.48; H, 8.64%).
Dienone 4c yellow oil; dH(300 MHz, CDCl3): 6.00^5.98 (m, 1H),
5.57 (s, 1H), 2.64^2.59 (m, 1H), 2.38^2.33 (m, 3H), 2.20^2.15 (m, 3H),
1.72^1.66 (m, 3H), 1.33-1.29 (m, 1H), 0.84 (t, 3H, J ˆ 6 Hz); dC
In summary, we have developed a simple one-step method
for the preparation of bicyclic dienones 4 in overall yield
higher than those obtained in our previous paper.4
O
O
R′
O
Et3N
K2CO3
R
O
O
O
EtOH, reflux
42–70%
EtOH, reflux
R
O
41–67%
3
4
OAc
R′
20–40%
+
R
K2CO3
1
2
EtOH, reflux
43–58%
3
3a
H
3b
3c
Et
3d8
H
3e8
H
Me
Me
R
R′
Me
Me
OMe
OEt
Yield of 4 (%)
48
58
52
43
46
Scheme 1
(75 MHz, CDCl3): 201.9, 154.8, 132.1, 131.7, 122.4, 47.8, 34.5, 30.5,
Experimental
‡
26.0, 23.2, 22.2, 11.5; MS: m/z 176 (M , 16), 148 (100), 120 (76),
1H NMR spectra were recorded in CDCl3 solutions at 60 or
300 MHz with tetramethylsilane as an internal reference. 13C NMR
were recorded at 75 MHz with CDCl3 as the internal reference.
Chemical shifts are given in ppm (d) and coupling constants J are
reported in Hz. IR spectra were obtained on a Perkin Elmer Paragon
1000 PC IR spectrometer. Mass spectra were measured on a
Hewlett-Packard 5890 spectrometer at 70 eV (EI). Column
chromatography was performed using silica gel 60 (70^230 mesh).
Preparation of Dienones 4.öA representative experimental proce-
91 (63), 77 (24) (Found: C, 81.9; H, 9.0. C12H16O requires C, 81.82;
H, 9.09%).
We thank Professor Labassi, T. (FST) for interesting and
valuable discussions.
Received, 15th March 1999; Accepted, 22nd April 1999
Paper E/9/02012H
dure for the preparation of 4a is described.
A mixture of
2-(acetoxymethyl)cyclohex-2-enone 1 (1.00 g, 6 mmol), pentane-2,4-
dione (0.684 g, 6 mmol), commercial anhydrous potassium carbonate
(3.32 g, 24 mmol) and 20 ml of absolute ethanol, was re£uxed for
References
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2
R. C. Klix and R. D. Bach, J. Org. Chem., 1987, 52, 580.
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K. Sarma, J. Am. Chem. Soc., 1991, 113, 4558.
* To receive any correspondence.
3
J. Colonge and P. Brison, Bull. Soc. Chim. Fr., 1961, 98.

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J. CHEM. RESEARCH (S), 1999 511
4
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F. Rezgui and M. M. El Ga|ed, Tetrahedron, 1997, 53, 15711
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4e (both equivalent to 4a), respectively; spectroscopic data
for compounds 3d and 3e are consistent with those reported
in ref. 4.
6
9
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