Studies on the Doebner-Miller, Skraup, and Related Reactions. I. Isolation of Intermediates in the Formation of Quinolines

Aniline and substituted anilines have been found to react, in acid solution, with αβ-unsaturated carbonyl compounds (or with substances which can be converted into αβ-unsaturated carbonyl compounds by acid) to give β-arylaminoaldehydes or ketones (IV, VIII, X), or in some cases the anil of a β-arylaminoaldehyde. These adducts have been cyclized, sometimes in good yield, to the corresponding quinolines: and the evidence indicates that compounds of these types must be intermediates m the Skraup, the Doebner-Miller, and related reactions. The mechanisms of these reactions are critically discussed. Satisfactory methods for the preparation of many quinolines have been devised, and syntheses of several new quinolines are reported.