Gassman's Intramolecular [2 + 2] Cationic Cycloaddition. Formal Total Syntheses of Raikovenal and epi-Raikovenal.

[摘要]：The first intramol. version of Gassman's cationic [2 + 2] cycloaddn. employing vinyl acetals tethered to an unactivated olefin and its application in the formal syntheses of raikovenal and epi-raikovenal are described. The two intermediates I and II for the total synthesis of raikovenal and epi-raikovenal were prepd.

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