Microwave‐Assisted Tandem Transformation on an Ionic‐Liquid Support: Efficient Synthesis of Pyrrolo/Pyridobenzimidazolones and Isoindolinone‐Fused Benzimidazoles

Abstract

A tandem transformation that involves the formation of three bonds and two heterocyclic rings in a one-pot fashion through amino-alkylation of an ionic-liquid-immobilized diamine with keto acids followed by successive double intramolecular cyclizations to afford a tricyclic framework has been explored. This tandem cyclization has been utilized to develop a rapid and efficient method to synthesize various pyrrolo[1,2-a]benzimidazolones and pyrido[1,2-a]benzimidazolones on an ionic-liquid support by using focused microwave irradiation. The application of this tandem cyclization was further extended to the aromatic keto acids to provide isoindolinone-fused benzimidazoles, a structurally heterogeneous library with skeletal diversity. The outcome of the cascade reaction was confirmed by the X-ray crystallographic study of the product directly attached to the ionic-liquid support. Use of the ionic liquid as a soluble support facilitates purification by simple precipitation along with advantages like high loading capacity, homogeneous reaction conditions, and monitoring of the reaction progress by regular conventional spectroscopic methods, whereas application of microwave irradiation greatly accelerates the rate of the reactions.

Heterocycles-Based Ionic Liquid-Supported Synthesis of Small Organic Molecules

“…IL-grafted 3-amino-4-hydroxy benzimidazolyl 100 was subjected with thiocarbonyl diimidazole under microwave irradiation followed by S-alkylation by various alkyl bromides at ambient temperature to afford IL-bound bis-benzimidazolyl benzoxazole 108 and subsequently basic methanolysis to remove IL support (Scheme 12) [45]. IL-grafted 3-amino-4-hydroxy benzimidazolyl 100 was subjected with thiocarbonyl diimidazole under microwave irradiation followed by S-alkylation by various alkyl bromides at ambient temperature to afford IL-bound bis-benzimidazolyl benzoxazole 108 and subsequently basic methanolysis to remove IL support (Scheme 12) [45].…”

Recent Progress of Microwave Irradiation in Synthesis and Diagnosis Treatment

“…A tandem transformation that involves the formation of three bonds and two heterocyclic rings in a one-pot fashion through amino-alkylation of an ionic-liquid-immobilized diamine with keto acids followed by successive double intramolecular cyclizations to afford a tricyclic framework has been explored. This tandem cyclization has been utilized to develop a rapid and efficient method to synthesize various benzimidazolones on an ionic-liquid support by using focused microwave irradiation.Use of the ionic liquid as a soluble support facilitates purification by simple precipitation along with advantages like high loading capacity, homogeneous reaction conditions, and monitoring of the reaction progress by regular conventional spectroscopic methods, whereas application of microwave irradiation greatly accelerates the rate of the reactions [16] .…”