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Synlett 2003(3): 0411-0413
DOI: 10.1055/s-2003-37124
LETTER
© Georg Thieme Verlag Stuttgart · New York

Synthesis of Bioactive Sesquiterpene Heliannuol E Involving a Ring-Expansion Reaction of Spirodienones

Fuminao Doi, Takahisa Ogamino, Takeshi Sugai, Shigeru Nishiyama*
Department of Chemistry, Faculty of Science and Technology, Keio University, Hiyoshi 3-14-1, Kohoku-ku, Yokohama 223-8522, Japan
Fax: +81(45)5661717; e-Mail: nisiyama@chem.keio.ac.jp;
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Publication History

Received 7 December 2002
Publication Date:
07 February 2003 (online)

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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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  • 13 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
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%), along with several by-products.