Asymmetric total synthesis of (-)-stenine and 9a-epi-stenine.

A route for the asymmetric synthesis of (-)-stenine, a member of the Stemona alkaloid family used as folk medicine in Asian countries, is described. The key features of the sequence employed include stereoselective transformations on a cyclohexane ring controlled by a chiral auxiliary unit and an intramolecular Mitsunobu reaction to construct the perhydroindole ring system. By using an intermediate in the route to (-)-stenine, an asymmetric synthesis of 9a-epi-stenine was also executed. The C(9a) stereocenter in 9a-epi-stenine was installed by using a Staudinger/aza-Wittig reaction of a keto-azide precursor followed by reduction of the resulting imine. The results of this effort demonstrate the applicability of the chiral auxiliary based strategy to the preparation of naturally occurring alkaloids that contain highly functionalized cyclohexane cores.

Asymmetric total synthesis of clavolonine.

The asymmetric total synthesis of clavolonine (1) has been achieved based on chiral auxiliary multiple-use methodology. Our synthetic route features stereoselective transformations on the cyclohexane ring utilizing the steric environment of the chiral auxiliary and an intramolecular Mannich reaction to construct the fused ring system.

Intramolecular iodoetherification of ene or diene ketals: facile synthesis of spiroketals.

A novel and rapid approach to chiral mono- or di-substituted spiroketals based on remote asymmetric induction by intramolecular iodoetherification of ene or diene ketals has been developed. This strategy concisely offers 5,5- and 5,6-spiroketals including the natural insect pheromone of the wasp.