Divergent total syntheses of pseudoberberine and nitidine through C[sbnd]H vinylation and switchable 6π electrocyclizations

Abstract

Quaternary protoberberine alkaloids and quaternary benzophenanthridine alkaloids are two biosynthetically related natural product families of biological importance. Although significant advances have been achieved in the synthetic chemistry of these alkaloids, a unified approach to these tetracyclic pyridinium-contained alkaloids remains elusive until our recent report. Herein, we report a concise, modular, divergent approach to two of them, pseudoberberine and nitidine, based on our newly developed strategy in five and seven steps. The key transformations include an Ag-promoted annulation, an isoquinoline-directed CH vinylation, and switchable aza-6π- or all-carbon-6π-electrocyclization.