Synthesis of Biologically Active Pyridoimidazole/Imidazobenzothiazole Annulated Polyheterocycles using Cyanuric Chloride in water

Abstract

An efficient and mild protocol for rapid access to N-fused polyheterocycles via Pictet-Spengler type 6-endo cyclization using cyanuric chloride in aqueous reaction medium has been developed. The protocol is successfully applied to a wide range of aryl/heteroaryl aldehydes (8a-o), ketones (10a-e), electron rich metallocene aldehyde (8e) and indoline-2,3-diones (12a-c) using cyanuric chloride (15-20 mol %) with tetra-n-butylammonium bromide (TBAB) (2.0 equiv.) as an additive at 80-90 ˚C to give polyheterocycles in good to excellent yield (66-92%). Moreover some of the synthesized compounds were found to exhibit antiplasmodial activity against chloroquine sensitive (CQ-S) 3D7 and chloroquine resistant (CQ-R) K1 strains of Plasmodium falciparum.