Abstract
A series of amido-acetals were reacted with the Brønsted superacid, CF3SO3H, to provides indolizidine derives by a cyclization cascade. A mechanism is proposed involving formation of a vinylogous enol which undergoes a 6π-electrocyclization reaction with an adjacent N-acyl iminium ion group. With aryl substituents, there is a strong tendency for the N-acyl iminium ion group to undergo Friedel-Crafts type cyclizations with the aryl group. The synthetic methodology was used to prepare the alkaloid natural product, ipalbidine.
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