An environmentally benign and atom-economical process to construct
a unique quinoline-based tetracyclic scaffold, through sequential
hydration-condensation-double cyclization reactions,
has been described. The reaction starts with readily available pyridine-substituted o-alkynylanilines and β-keto
esters, promoted by p-toluenesulfonic
acid in ethanol in one pot. In the absence of β-keto esters,
multisubstituted quinolines are formed bimolecularly in reasonable
yields.
alkynes - cyclization - heterocycles - quinoline - tandem reaction