Stereoselective Construction of Copaborneol and Longiborneol Frameworks by Intramolecular Double Michael Reaction.
Stereoselective syntheses of tricyclo[5.3.0.0(3,8)]decane 22 and tricyclo[6.3.0.0(3,9)]undecane 26, the basic skeletons of copaborneol and longiborneol, were achieved by the intramolecular double Michael reactions of 2-cyclopenten-1-ones 15-17. The substrates were prepared starting with tricyclo[5.2.1.0(2,6)]deca-4,8-dien-3-one (6). The intramolecular double Michael reactions were carried out under three different conditions: TMSCl-Et(3)N-ZnCl(2), TMSI-(TMS)(2)NH, and Bu(2)BOTf-(TMS)(2)NH. The framework 26 of longiborneol was constructed in good yields using the latter two reagent systems.
Ihara
Masataka
M
Pharmaceutical Institute, Tohoku University, Aobayama, Sendai 980-77, Japan.
Makita
Kei
K
Fujiwara
Yuki
Y
Tokunaga
Yuji
Y
Fukumoto
Keiichiro
K