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Synthesis 2011(5): 715-722  
DOI: 10.1055/s-0030-1258412
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© Georg Thieme Verlag Stuttgart ˙ New York

Total Syntheses of (±)-(Z)- and (±)-(E)-9-(Bromomethylene)-1,5,5-trimethylspiro[5.5]undeca-1,7-dien-3-one and (±)-Majusculone

Jia-Liang Zhu*a, Po-Wei Huanga, Ruei-Yi Youa, Fa-Yan Leea, Sheng-Wei Tsaoa, I-Chia Chenb
a Department of Chemistry, National Dong Hwa University, Hualien 974, Taiwan, R. O. C.
Fax: +886(3)8633570; e-Mail: jlzhu@mail.ndhu.edu.tw;
b Department of Cosmetic Applications and Management, Cardinal Tien College of Healthcare and Management, Taipei, Taiwan, R. O. C.
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Publication History

Received 16 November 2010
Publication Date:
18 January 2011 (online)

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Abstract

A new total synthesis of the chamigrene sesquiterpenoids (Z)-9-(bromomethylene)-1,5,5-trimethylspiro[5.5]undeca-1,7-diene-3-one and its 15-E-epimer has been accomplished in 13 steps. In our sequence, a Diels-Alder reaction and subsequent reductive alkylation of the resulting adduct was utilized as the key strategy to create the A-ring and the quaternary spirocenter with the suitable functionalities for accessing the B-ring. Additionally, from the advanced intermediate, a total synthesis of (±)-majusculone, a nor-chamigrene natural product, was also readily achieved in two steps.

Key words

chamigrenes - sesquiterpenes - majusculone - total syntheses - Diels-Alder reaction

11

To resolve the stereochemistry of 11, we further converted it into (3S*,5S*)-3,5-dimethyl-4-acetylcyclohexanone by treating with TBAF in THF. Given with the fixed trans relationship between the C-4 acetyl and C-3 methyl groups, the relative steric relationships between the C-5 methyl and the C-4 acetyl groups could be deduced from the coupling constants of C-4 methine proton at δ = 2.72 (dd, J = 9.1, 3.7 Hz) from the ¹H NMR spectrum (see Supporting Information).