One-pot,three-component cascade synthesis of new tetrasubstituted pyrroles by coupling reaction of 2-functionally substituted 2-alkenals,amines, and nitroethane

The reactivity of 2-alkylthio(2-alkoxy)-substituted 3-aryl(hetaryl)propenals in a one-pot, three-component reaction with primary amines and nitroethane has been studied. A method for the synthesis of highly functionalized pyrroles (in 36–80% yield) from 2-alkylthiopropenals has been developed on the basis of this reaction. It is found that the reaction proceeds via formation of the intermediate imine of the starting enal, which undergoes 1,2-addition by nitroethane to give kinetically controlled 2-alkylthio-3-alkylamino-1-aryl(hetaryl)-4-nitropentene. When left to stand, upon heating or under microwave assistance, this adduct can be transformed into the thermodynamically controlled 1,4-adduct. The latter undergoes intramolecular cyclization to afford the target pyrrole. A possibility of such isomerization of addition products of nitroalkane to 2-functionalized α,β-unsaturated imines is revealed for the first time. Scope of the reaction depending upon its conditions as well as structure of the starting substrates and amines has been studied.