M.-J. Ferna´ndez et al. / Tetrahedron Letters 42 (2001) 891–893
893
Cl
CH2
α,p−coupling
CH2
[4+2]
2
Scheme 5.
ing as a leaving group. In both mechanisms, the same
intermediate is generated that, after a [4+2] cycloaddi-
tion, yields lepidopterene 2.
7. Kaupp, G.; Schmitt, D. Chem. Ber. 1980, 113, 3932.
8. Lepidopterene was isolated directly from the reaction
mixture by removal of the solvent and precipitation with
diethyl ether. Purification was carried out by crystalliza-
tion from chloroform. Analytical data matched the
reported structure.
With the aim of establishing which is the predominant
pathway, we carried out the reaction in dry acetone at
reflux but using this time only 0.5 equiv. of sodium
9. Compound 4 is unstable and decomposes on standing. 1H
NMR (300 MHz, CDCl3, 25°C): l 8.32 (s, 1H, H-10),
8.04 (d, J=8.9 Hz, 2H, H-4, H-5), 7.86 (d, J=8.5 Hz,
2H, H-1, H-8), 7.51 (app t, 2H, H-2, H-7), 7.30 (app t,
2H, H-3, H-6), 5.29 (s, 2H, CH2); MS (EI, 70 eV) m/z
191 (M+−I, 100), 127 (26).
iodide. As
a result, a total consumption of 9-
(chloromethyl)anthracene was observed and lepi-
dopterene and 1,2-bis(9-anthracenyl)ethane were
obtained in 66 and 9% yield, respectively. This fact
indicates that a total conversion of 9-(chloromethyl)
anthracene into 9-(iodomethyl)anthracene is not
required in the formation of lepidopterene and supports
the second pathway. Moreover, a catalytic amount of
sodium iodide was not enough to produce lepi-
dopterene from 9-(chloromethyl)anthracene beyond a
2% yield, which invalidates the possibility of an auto-
catalytic process.
10. Compound 5 has been recently synthesized by Sampath
Kumar, H.M.; Subba Reddy, B.V.; Jagan Reddy, E.;
Yadav, J.S. Green Chem., 1999, 1, 141, but up to now
characterization has not been reported. mp (petroleum
1
ether/ethyl acetate) 150–152°C dec. H NMR (300 MHz,
CDCl3, 25°C): l 8.45 ( s, 1H, H-10), 8.15 (m, 2H, H-1,
H-8), 8.04 (m, 2H, H-4, H-5), 7.46 (m, 4H, H-2, H-3,
H-6, H-7), 6.74 (d, J=8.6 Hz, 1H, H-6%), 6.51 (dd,
J=8.6, 3.0 Hz, 1H, H-5%), 5.85 (d, J=3.0 Hz, 1H, H-3%),
4.90 (s, 2H, CH2). 13C NMR (75 MHz, CDCl3, 25°C): l
149.50 (C-1%), 146.82 (C-4%), 131.63 (C-4a, C-5a or C-8a,
C-9a), 131.23 (C-9), 130.68 (C-4a, C-5a or C-8a, C-9a),
129.08 (C-4, C-5), 128.45 (C-2%), 126.59 (C-10), 125.97
(C-3, C-6), 124.99 (C-2, C-7), 124.75 (C-1, C-8), 116.27
(C-3%), 115.66 (C-6%), 113.39 (C-5%), 27.09 (CH2); MS (EI,
70 eV) m/z 300 (M+, 15), 178 (100).
Acknowledgements
Support of this research by the CICYT (Project SAF96-
1704) and the Universidad de Alcala´ (Project E 039/
2000) is gratefully acknowledged. LG thanks to
Universidad de Alcala´ for a predoctoral fellowship. The
authors thank Dr. Cristo´bal Lo´pez for helpful
comments.
11. Yorimitsu, H.; Nakamura, T.; Shinokubo, H.; Oshima, K
J. Org. Chem. 1998, 63, 8604 and references therein.
12. Compound 8 was isolated by chromatography on silica
gel with hexane:ethyl acetate (99:1) and purified by
recrystallization from 2-propanol, mp 114–115°C. IR
(KBr) 3049, 3001, 2971, 2928, 2867, 1624, 1525, 1479
References
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