Aza-Henry and aza-Knoevenagel reactions of nitriles for the synthesis of pyrido[1,2-a]indoles†
N-(Propargyl)indole-2-carbonitriles undergo DBU-catalyzed addition of CH-acids to nitriles, followed by cyclization to give 9-aminopyrido[1,2-a]indoles. The reaction proceeds through the initial formation of a push–pull enamine, alkyne–allene rearrangement and intramolecular nucleophilic cyclization. Nitromethane and malonate esters can be employed as the CH-acids. The resulting compounds were found to exhibit fluorescence properties.