Versatile Syntheses of Quinolines by Annulation of Pyridines. Synthesis of Furo- and -quinolines

Article abstract of DOI:10.1021/jo00154a004

A new, versatile annulation route for the synthesis of substituted quinolines has been developed by using regioisomeric bifunctional pyridine derivatives with vicinal bromomethyl and (phenylsulfonyl)methyl groups.The sequence consists of (a) alkylation of substituted diethyl malonates with these (bromomethyl)pyridines and (b) intramolecular acylation with concomitant decarboxylation and leads to quinoline derivatives variously substituted in the carbocycle.A simultaneous desulfurization-aromatization of the carbocycle has been developed for these cyclized sulfones.5-(Phenylsulfonyl)-7-allyl-6-quinolinol (30), obtained via this cyclization and dehydrogenation, was then used for the preparation of furo<2,3-g>quinoline derivatives.The novel parent systems furo<2,3-g>- and -<3,2-g>quinoline (38 and 40) were obtained in good yield in a one-operation acid-induced cyclization-elimination sequence from the bicyclic annulation products 22 and 28, respectively.