Study On Green Process For Synthesis Of Pyridines

Methylene-bridged bis-1,3-dicarbonyl compounds are useful building blocks or intermediates for transition-metal complexes and organic synthesis.Heterocyclic compounds play an important role in nature because of thequantity is huge.Among nitrous heterocyclic compounds,pyridine compounds have attracted a large number of chemists to explore new synthesis methods with green chemistry owing to their great values in pharmaceutical industry,pesticide industry and food additives industry.We described highly convergent one-pot synthesis of Hantzschtype pyridines has been developed based on a three-componentannulation of 1,3-dicarbonyl compounds,DMSO,and ammonium salt,which involving a transitionmetalfree oxidative methylenation reaction/Hantzsch pyridine synthesis cascade reaction.This intermolecular annulation reaction proceeds under mild conditions,wherein DMSO serves as solvent,methylenation reagent,and oxidant.Fully unsaturated monocyclic 1,4-oxazepines A are unstable and hard to be obtained by traditionally synthetic methods due to their antiaromatic character.We have developed a highly attractive and operationally simple inter-or intramolecular capture of in situ generated 1,4-oxazepines cascade reaction to construct 2-alkoxy pyridines and dihydrofuro[2,3-b]pyridines with readily available substrates.The transformation showed a wide range of functional-groups tolerance,including iodide,terminal alkyne,and free amine.This environmentally friendly procedure proceeded under metal-free conditions and generated H₂O as sole byproduct.