Catalytic application of recyclable silica-supported bismuth(III) chloride in the benzo[N,N]-heterocyclic condensation

• Immobilization of Bi(III) ion onto silica surface.
• Formation of –O–BiOCl as stable Lewis acid sites.
• Protocol applicability to a wide range of arene-1,2-diamines as substrate.
• Low catalyst loading with high activity.
• Catalyst recycled four times without any significant loss in activity.

Silica-supported bismuth(III) chloride (BiCl3/SiO2) has been successfully employed in the condensation of 1,2-dicarbonyls with a variety of arene-1,2-diamines bearing either electron withdrawing or donating functional groups. The catalyzed reaction proceeded smoothly under ambient temperature in methanol to give the corresponding quinoxaline and pyrido[2,3-b]pyrazine compounds in good to excellent yields. The catalyst exhibited remarkable reusable activity and higher catalytic performance than homogeneous BiCl3. A plausible mechanism for the catalytic action of BiCl3/SiO2 has been introduced. Moreover, the crystal structure of the prepared unsymmetrical benzo[N,N]-heterocycles has been determined by single crystal X-ray diffraction.

A convenient combination of (NH4)6Mo7O24 and PEG was used as an efficient polar paste catalyst system for tandem synthesis of quinoxalines and pyrido[2,3-b]pyrazines under open-vessel focused microwave irradiation. Low conversions were obtained when (NH4)6Mo7O24 or PEG was used individually.Figure optionsDownload as PowerPoint slide