Base-Promoted Transannulation of Heterocyclic Enamines and 2,3-Epoxypropan-1-ones: Regio- and Stereoselective Synthesis of Fused Pyridines and Pyrroles

Base-promoted
transannulation of heterocyclic enamines and 2,3-epoxypropan-1-ones
has been successfully achieved, providing a new access to structurally
diverse fused pyridines and pyrroles with excellent regio- and stereoselectivity.
Treatment with N-aryl 4-aminofuran-2­(5H)-ones and 2,3-epoxypropan-1-ones under microwave heating resulted
in functional furo­[3,2-b]­pyridines in good
yields. The N-aryl 4-aminopyrrol-2­(5H)-ones bearing an electron-withdrawing group engaged in the reaction
afforded pyrrolo­[3,2-b]­pyridines, whereas their
counterparts with an electron-neutral or an electron-donating group
underwent a different reaction pathway to form pyrrolo­[3,2-b]­pyrroles through C–C bond cleavage.