A versatile new synthesis of quinolines and related fused pyridines, Part 5. The synthesis of 2-chloroquinoline-3-carbaldehydes

Abstract

Acetanilides are converted into 2-chloroquinoline-3-carbaldehydes in good yield by the action of Vilsmeier's reagent in phosphoryl chloride solution. The reaction is shown to involve successive conversion of the acetanilide in to an imidoyl chloride and then an N-(α-chlorovinyl)aniline. The latter enamine is diformylated at its β-position and subsequently cyclised to the chloroquinolinecarbaldehyde. The diformylated intermediates may be isolated in several cases and separately cyclised with polyphosphoric acid.