Merging C-H Vinylation With Switchable 6 Pi-Electrocyclizations For Divergent Heterocycle Synthesis

Pyridinium-containing polyheterocycles exhibit distinctive biological properties and interesting electrochemical and optical properties and thus are widely used as drugs, functional materials, and photocatalysts. Here, we describe a unified two-step strategy by merging Rh-catalyzed C-H vinylation with two switchable electrocyclizations, including aza-6 pi-electrocyclization and all-carbon-6 pi-electrocyclization, for rapid and divergent access to dihydropyridoisoquinoliniums and dihydrobenzoquinolines. Through computation, the high selectivity of aza-electrocyclization in the presence of an appropriate "HCl" source under either thermal conditions or photochemical conditions is shown to result from the favorable kinetics and symmetries of frontier orbitals. We further demonstrated the value of this protocol by the synthesis of several complex pyridinium-containing polyheterocycles, including the two alkaloids berberine and chelerythrine.