Novel approach towards the synthesis of skeletally diverse benzimidazole-pyrrolo[1,2-a]quinoxaline by S_NAr/Pictet-Spengler reaction under focused microwave irradiation

In a study aimed at developing a novel concise approach to the benzimidazole-pyrrolo[1,2-a]quinoxaline core of medicinal interest, a Pictet-Spengler reaction has been identified that gives direct access to the target compound on soluble polymer support under focused microwave irradiation. The pyrrole moiety has been introduced on polymer immobilized benzimidazole derivatives by S_NAr diversification which subsequently transformed to the title compounds via reduction followed by Pictet-Spengler cyclisation with various ketones in good yields and excellent purity. The work described here demonstrates the versatility of the base mediated S_NAr reaction coupled with Pictet-Spengler cyclisation in the construction of novel heterocycles.