Highly modular assembly of cationic helical scaffolds: rapid synthesis of diverse helquats via differential quaternization

A protocol for rapid and highly modular assembly of a diverse set of helquats is described. From a common bis-isoquinoline precursor, two successive distinct pyridine-type nitrogen quaternizations followed by rhodium-catalyzed [2+2+2] cycloaddition afford non-symmetric [7]helquats. This route allows for straightforward molecular editing of cationic helical skeletons as exemplified by the synthesis of 15 different [5]-, [6]-, and [7]helquats.