The Reactions of Electron‐Rich Heterocycles with Derivatives of Orthocarboxylic Acids; VIII. Proton Acid‐Catalyzed Acylation of Indoles by 2‐Alkoxy‐1,3‐dioxolanes

In acid‐catalyzed reactions with 3‐unsubstituted indoles 1, 2‐alkoxy‐1,3‐dioxolanes 2a‐c behave as acyl equivalents. Depending on the substitution patterns of the reaction partners, the 1,3‐dioxolanium ions 3a‐c, generated in situ from the cyclic ortho esters by the action of sulfosalicylic acid, react to form tris‐(3‐indolyl)alkanes 6 and 9, bis‐(3‐indolyl)ethenes 7, or 3‐benzoylindoles 8. Analogous reactivity was observed with related acyclic ortho esters.