Rhodium-Catalyzed Regioselective Synthesis of Isoindolium Salts from 2-Arylpyridines and Alkenes in Aqueous Medium under Oxygen

Article abstract of DOI:10.1002/adsc.201600452

A highly regioselective synthesis of pyrido[2,1-a]isoindolium salts from 2-arylpyridines and two equivalents of electron-deficient alkenes catalyzed by rhodium is demonstrated. The reaction was carried out in aqueous medium at 110 °C using inexpensive oxygen as oxidant. Reverse aza-Michael addition of the isoindolium salt occurs when the salt was treated with base to give a β-disubstituted alkene product. A reaction mechanism involving an ortho C–H olefination of 2-arylpyridine by alkene, intramolecular aza-Michael addition, deprotonation at the β-carbon of the alkene fragment followed by another Michael addition to give the final product is proposed. (Figure presented.).