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.

Palladium-Catalyzed α,ß-Dehydrogenation of Esters and Nitriles.

A highly practical and general palladium-catalyzed methodology for the α,ß-dehydrogenation of esters and nitriles is reported. Generation of a zinc enolate or (cyanoalkyl)zinc species followed by the addition of an allyl oxidant and a palladium catalyst results in synthetically useful yields of α,ß-unsaturated esters, lactones, and nitriles. Preliminary mechanistic investigations are consistent with reversible ß-hydride elimination and turnover-limiting, propene-forming reductive elimination.