Diastereoselective synthesis of highly functionalized quinolizines via a pyridine-based three-component reaction and a DFT investigation on the reaction mechanism

Novel, one-pot, three-component reactions of the zwitterions generated in situ from pyridine and acetylenic esters with alkoxymethylenemalononitriles via 1,4-dipolar cycloadditions are described. The reactions afforded dialkyl 1,1-dicyano-2-alkoxy-1,9a-dihydro-2H-quinolizine-3,4-dicarboxylate derivatives in good to high yields without using any catalyst or activation. Structural, electronic, energetic, and mechanistic details of the reaction are also revealed by density functional theory (DFT) calculations, which strongly support the exclusive formation of the observed products. (C) 2013 Elsevier Ltd. All rights reserved.