DBU-Catalyzed One-Pot Domino Synthesis of Polycyclic Benzofuran(thiophene)-pyridine-Fused Indolizines

Herein, we have developed a DBU-catalyzed, iterative C–C/C–C/C–N/C–N bond forming domino reaction of 2-(pyridin-2-yl)acetonitrile, 2-aroyl-benzofuran-3-carbaldehyde/2-aroyl-benzothiophene-3-carbaldehyde, and trimethylsilyl cyanide that directly furnishes polycyclic benzofuran(thiophene)-pyridine-fused indolizines. This one-pot domino protocol efficiently enables a Knoevenagel condensation and concomitant [4 + 1] cycloaddition/cyclization cascade under very mild and simple reaction conditions, thereby paving the way for the fusion of five- and six-membered rings within a single molecular structure. The resultant products do not require chromatographic purification, as they can be crystallized directly from the reaction mixture using ethanol.