Quinoline conjugated imidazopyridine and pyridopyrimidine synthesis in water as highly selective fluoride sensors via a catalyst-free four-component reaction

A green and convenient procedure for the synthesis of quinoline-conjugated imidazopyridines and pyridopyrimidines has been developed by a simple one-pot reaction in the absence of any transition metal catalyst in water. This green process can be readily performed by reacting inexpensive starting materials of 2-chloroquinoline-3-carbaldehyde, malononitrile, 1,1-bis(methylthio)-2-nitroethylene, and diamine in aqueous solution. The present synthesis shows attractive characteristics, such as the use of water as reaction media, convenient one-pot operation, and reduced waste production without the use of any base or metal promoters. The products are purified by crystallization from ethanol, and the process does not involve any hazardous solvent. Also, the fluorescence study of these conjugated systems was also considered, which revealed that they have highly selective sensing of fluoride.