1004
Can. J. Chem. Vol. 85, 2007
nol (12.5 mL) (saturated with hydrochloric acid) was irradi-
ated at 25 W with a ramp period of 1 min until reflux was
reached. Heating of the solution was then maintained for
30 min, and after cooling the solvent was removed in vacuo.
The various products observed by TLC analysis were then
separated by column chromatography (petroleum ether) and
analyzed as in previous procedure. Yield of 13c 15%.
Microwaves
Microwave experiments were carried out at atmospheric
pressure using a focused microwave reactor (CEM Dis-
cover™) (28) or MAP technology (14, 15). The instrument
consists of a continuous focused microwave power output
from 0 to 300W. Reactions were performed in a glass vessel
equipped with a condenser; it is also possible to work under
dry atmosphere, in vacuo, or under pressure (0–20 torr, tubes
of 10 mL, sealed with a septum) (1 torr = 133.322 4 Pa).
The temperature content of a vessel is monitored using a cal-
ibrated IR sensor mounted under the vessel. All experiments
were performed using stirring option whereby the contents
of a vessel are stirred by means of a rotating plate located
below the floor of the microwave cavity and a Teflon-coated
magnetic stir bar in the vessel. In all experiments a power of
300 W was selected and the reflux temperature was reached
with a ramp of about 1 min. The time of the reaction does
not include the ramp period.
Acknowledgments
We would like to thank A. Savoie (U de Moncton) for
helpful discussion and his involvement in the primary stage
of this study, S. Arseneau (U de Moncton) for some molecu-
lar modelling and energy computing calculations and C.
Fajolles (CEA) for precious graphical assistance. One of the
authors (TB) thanks CEM Corp. for multiform support and
technical assistance. The generous financial support of Envi-
ronment Canada through Youth Horizons Fellowship was
greatly appreciated.
Synthesis
References
(4,10a-dimethyl-7b-iso-propyl-decaline-5ene)1a,4a-maleic
acid anhydride (9b)
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Diels–Alder condensation of 1 with maleic anhydride
(thermal reaction). Cubebene (1) (100 mg, ca. 0.5 mmol)
and maleic anhydride (40 mg, 0.45 mmol, less than
equimolar ratio) were dissolved in anhydrous toluene and
heated in the stainless vessel for 24 h at 130 °C. Two con-
secutive flash column chromatography separations on silica
gel column of adduct 9b were then performed on the oily
residue under TLC (hexane/ether 9:1, Rf = 0.7) and GC-MS
controls (using mass chromatogram at m/z 302). The yield of
pure adduct 9b was 12% (16–18 mg) with an optical rotation
of α25 = +38° (ethanol). MS eight main ions in 9b, EI-
spectrum m/z (I%): 302 (12, M+), 274 (72), 259 (16), 231
(56), 203 (100), 185 (17), 164 (82), 145 (39).
Diels–Alder condensation of 1 with maleic anhydride (mi-
crowave reaction). Yield of 9b 15%–23%. Conditions: CEM
Discover™ 300 W at the reflux temperature of toluene for
5–30 min.
4,10-dichloro-4␣,10␣-dimethyl-7-iso-propyl-trans-
decalin (13c)
Addition of HCl to 1 at 0–5 °C. To a solution of α-
cubebene (1) (90 mg, 0.5 mmol) in methanol (20 mL) (the
equal volume of dry methanol saturated with hydrochloric
acid (g) was added). The reaction mixture was left at 0–5 °C
for 24 h then cautiously evaporated in vacuo. The resulting
product 13c (14 mg), mp 104–107 °C, TLC: petroleum
ether, Rf = 0.4, isolated by column then by preparative TLC
chromatographies on silica gel, yield 25%. In this separa-
tion, 31 mg of starting compound 1 and three unidentified
compounds were separated. MS: For the compound 13c CI-
MS (NH3) mass spectra revealed the presence of m/z 294
7. J.A. Hirsch. Concepts in theoretical organic chemistry. Allyn
and Bacon, Boston, Mass. 1974. Chap. 3. pp. 77–78.
8. H.R. Sonawane, N.S. Bellur, D.G.T. Kulkarni, and J.R. Ahuja.
Synlett, 12, 875 (1993).
+
(100, NH4 ), 277 (3, MH+) 276 (2). The ESI spectrum con-
firmed double chlorination at m/z 277 (55, MH+) and 279
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(35, MH+).
Phytochemistry, 44, 1291 (1997).
10. A.M. Adio, C. Paul, H. Tesso, P. Kloth, and W.A. König. Tet-
rahedron: Asymmetry, 15, 1631 (2004).
Addition of DCl to 1 was performed in a similar mode
(also see ref. 3).
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6833 (2005); (b) A. Padwa and S. Clough. J. Am. Chem. Soc.
92, 5803 (1970).
Synthesis by microwave-assisted addition of HCl
A solution of α-cubebene (100 mg, 0.5 mmol) in metha-
© 2007 NRC Canada