Iron(III)-Catalyzed Methanesulfonic-Acid-Mediated [3 + 2 + 1C] Annulation of Enaminones with 1,3-Dioxolane: Access to 2-Hydroxy-1,2-dihydropyridines

An iron(III)-catalyzed methanesulfonic-acid-mediated [3 + 2 + 1C] annulation of enaminones assembling a 1,2-dihydropyridine (1,2-DHP) scaffold has been developed for the first time. This approach facilitates the rapid synthesis of 2-hydroxy-1,2-DHP derivatives in moderate to excellent yields with a broad substrate scope under mild conditions. The employment of 1,3-dioxolane as both a 1C synthon and solvent enables simultaneous incorporation of both a carbon atom and a hydroxy group into 1,2-DHPs. Application potential of this protocol is proven by its gram-scale preparation and further derivatizations.