Intramolecular Vilsmeier processes: a new route to cyclopenta[b]- and cyclohexa[b]-fused quinolines by cyclisation of adipic and pimelic bis-amides

Abstract

Symmetrical and unsymmetrical bis-amides derived from adipic and pimelic acid and secondary amines react in POCl₃ solution to give the title compounds by way of a Vilsmeier reagent–α-chloro enamine interaction. Adipanilide and pimelanilide only cyclise with added PCl₅. However the bis-N-substituted derivatives (N-methyl or N-phenyl) of adipanilide and pimelanilide give quinolinium salts in good yield. Unsymmetrical amides with an N-substituted anilide at one end and an aliphatic unit at the other only proceed as far as the intermediate stage, giving 1,2-disubstituted cyclo-pentanes or -hexanes. Analogous amides derived from suberic and sebacic acid do not give quinolinium salts but instead give complex mixtures.