Facile and stereoselective access to nonracemic tricyclic cyclobutanes by asymmetric intramolecular Michael-aldol reaction: thermodynamic equilibrium and activation by iodonium ion.
Intramolecular Michael-aldol reactions of (-)-phenylmenthyl enoates tethered to cycloalkanone affords tricyclic cyclobutanes with high degrees of diastereochemical control. Kinetic and thermodynamic studies revealed that the Michael-aldol reaction is reversible under conditions in which trimethylsilyl iodide is used in the presence of hexamethyldisilazane at ambient temperature. Different levels of diastereoselectivity are observed when this cyclization process is carried out under kinetic vs thermodynamic conditions. Finally, an influence of added iodonium donors on the reaction rate has been noted.
Takasu
K
K
Department of Organic Chemistry, Graduate School of Pharmaceutical Sciences, Tohoku University, Aobayama, Sendai 980-8578, Japan. kay-t@mail.pharm.tohoku.ac.jp
Ueno
M
M
Ihara
M
M