One-Pot Three-Component Synthesis of Highly Functionalized 2,3-Dihydro-1,3-dioxo-1H,5H-pyrazolo[1,2-a][1,2,4]triazoles

The reactive 1 : 1 zwitterionic intermediate formed by the addition of isocyanides to dialkyl acetylenedicarboxylates was trapped with 4-arylurazoles to produce the highly functionalized pyrazolo[1,2-a][1,2,4]triazoles 5 in good yields (Table). The structures of the products 5a–h were corroborated spectroscopically (IR, 1H- and 13C-NMR), by EI-MS, and elemental analysis. A possible mechanism for this reaction is proposed (Scheme).