A convergent approach to batzelladine alkaloids. Total syntheses of (+)-batzelladine E, (-)-dehydrobatzelladine C, and (+)-batzelladine K

We recently reported a convergent strategy to access the polycyclic guanidinium alkaloid (+)-batzelladine B via an aldol addition retro-aldol aza-Michael addition cascade. Here we describe the application of this approach toward the total syntheses of (+)-batzelladine E, (-)-dehydrobatzelladine C, and (+)-batzelladine K. The identification of suitable methods to functionalize a common tropane core by electrophilic alkynylation and nucleophilic 1,2-addition were essential to generalizing this approach. We provide evidence for the intermediacy of an acylallene species in the cascade reaction. (C) 2018 Published by Elsevier Ltd.