Construction of the Tetracyclic Framework of Sulfur-Containing Discorhabdin-Type Alkaloids.

Herein, we report an efficient synthetic method for constructing the tetracyclic scaffold of sulfur-containing discorhabdin-type alkaloids. The key to success is the BF 3 •Et 2 O-promoted dienone-phenol-type rearrangement/sulfur insertion cascade reaction, which converts the common and readily available N,O -acetal-bridged tetracyclic framework to the labile and synthetically challenging N,S -acetal-bridged tetracyclic framework in a single step. Additionally, the hypervalent iodine promoted intramolecular oxidative dearomatization terminated with amide and indium(III) acetate-facilitated radical cyclization were also essential elements in this study.