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.

中文翻译：

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超强酸促进的吲哚并咪唑衍生物的合成

一系列酰胺基乙缩醛与布朗斯台德超酸CF ₃ SO ₃ H反应，通过环化级联反应提供吲哚并咪唑衍生物。提出了一种机理，该机理涉及形成乙烯基的烯醇，该乙烯基的烯醇与相邻的N-酰基亚胺离子基团进行6π-电环化反应。在具有芳基取代基的情况下，N-酰基亚氨基鎓离子基团具有与芳基基团一起进行Friedel-Crafts型环化的强烈趋势。合成方法用于制备生物碱天然产物ipalbidine。