Abstract
A heliannane-type sesquiterpene, heliannuol E (1),
has been successfully synthesized. The key step was conversion of
the electrochemically produced spiro compounds (8,
and 18) into the corresponding dihydrobenzopyrans
(11, 12, 19, and 20) by
a selective ring expansion process.
Key words
heliannuol E - anodic oxidation - sesquiterpene - dihydrobenzopyran - two-electron oxidation
References
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9 The ortho-bromophenol
derivative without methyl groups, might be available: the bromo
substituent would be converted into the appropriate alkyl group.
Although this method would require a rather longer synthetic process,
the feasibility of the method is under consideration.
10 Despite similar CV curves (first peak:
ca. 1.05 V vs SCE), 5 and 7 provided
different oxidation reactions.
11 Several unknown by-products were observed.
Upon employing acetone as a solvent, anodic oxidation of 7 provided 8 (40%),
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Selected Spectroscopic
Data. Compound 8: 1H NMR (CDCl3): δ = 2.01
(3 H, d, J = 1.5
Hz), 2.1 (4 H, complex), 4.15 (2 H, t, J = 6.6
Hz), 6.67 (1 H, dd, J = 3,
1.5 Hz), 7.29 (1 H, d, J = 3
Hz).
Compound 11: 1H
NMR (CDCl3): δ = 2.00 (2 H, complex), 2.16
(3 H, s), 2.61 (t, J = 6.6
Hz), 4.06 (2 H, t, J = 5
Hz), 6.82 (1 H, s).
Compound 12: 1H
NMR (CDCl3): δ = 2.00 (2 H, complex), 2.20
(3 H, s), 2.69 (2 H, t, J = 6.6
Hz), 4.06 (2 H, t, J = 5
Hz), 6.59 (1 H, s).
Compound 1: 1H
NMR(CDCl3): δ = 1.24 (3 H, s), 1.30
(3 H, s), 1.9 (2 H, complex), 2.20 (3 H, s), 3.46 (1 H, m), 3.74 (1
H, dd, J = 3.6,
10 Hz), 4.91 (1 H, dd, J = 17,
1.5 Hz), 5.11 (1 H, dd, J = 10.4,
1.5 Hz), 5.97 (1 H, ddd, J = 17,
10.4, 6.4 Hz), 6.49 (1 H, s), 6.66 (1 H, s). The spectroscopy was superimposable
to the reported one. Found: m/z = 248.1428. Calcd for C15H20O3 (M):
248.1412.
Compound 23: 1H
NMR(CDCl3): δ = 1.26 (3 H, s), 1.31
(3 H, s), 1.65 (1 H, q, J = 12
Hz), 2.01 (1 H, br dd. J = 11.7,
12 Hz), 2.19 (3 H, s), 3.48 (1 H, m), 3.80 (1 H, br d, J = 17 Hz), 5.20
(1 H, br d, J = 10
Hz), 5.24 (1 H, br d, J = 17
Hz), 5.68 (1 H, ddd, J = 17,
10, 9.8 Hz), 6.60 (1 H, s), 6.64 (1 H, s). Found: m/z = 248.1416. Calcd for C15H20O3 (M):
248.1412
