Stereoselective tandem synthesis of oxazolo-fused pyrroloquinolines from o-alkynylaldehydes via Ag(I)-catalyzed regioselective 5-exo-dig ring closure

A tandem approach for the regio- and stereoselective synthesis of oxazolo-fused pyrroloquinolines 3a-l via the reaction of o-alkynylaldehydes 1a-i with chiral amino alcohols 2a-c under mild reaction conditions is described. The possible participation of pyridine ring in the regioselective formation of 5-exo-dig cyclized products was supported by the control experiments. The structures and stereochemistry of the products were confirmed by NOESY and X-ray crystallographic studies.