Asymmetric Synthesis Using Acetals : Formation of Chiral Oxonium Ion

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Formations of chiral oxonium ion intermediates by intramolecular haloetherification of ene acetals and their applications have been investigated.As an application of the chiral, non-racemic cyclohexene acetal obtained by an intramolecular haloetherification reaction of cyclohexadiene acetal from 3-(1,4-cyclohaxadien-3-yl)propanal and chiral hydrohenzoin, synthetic work of stemona alkaloids was held. As a result, 9a-epi-stenine has been achieved, and the synthesis of stenine itself is on the last stage. From the intermediate of their syntheses, the epoxy cyclohexenone core of scyphostatin having N-Smase inhibiting activity was synthesized.Furthermore, an unexpected domino intramolecular haloetherification reaction of acyclic σ-symmetic diene acetals was found, and the tetrahyderofurans having four asymmetric centers were obtained in one-pot operation.