S. A. Yamashkin

Closure of the pyridine ring in the combes quinoline synthesis (Review)

Closure of the pyridine ring in the Combes quinoline synthesis occurs by a type of intramolecular electrophilic substitution. With two free ortho positions the direction of ring formation depends both on the initial electrophilic attack, i.e., the nucleophilicity of the ortho carbon atom, and on the possibility of stabilizing the intermediate complex. The steric requirements of substituents both in the enaminoketone chain and in the position ortho to the point of attack exert a significant effect on the direction of ring closure. The steric factor is decisive when forming condensed angular quinoline structures.

3-(indolylamino)vinyl ketones

The reaction of 5- and 6-aminoindoles with 1,3-diketones leads to 3-(indolylamino)vinyl ketones, which have an enamino ketone structure. A study of the mass-spectral fragmentation of the enamino ketones makes it possible to unambiguously determine the direction of the reaction and also to distinguish and identify isomeric pairs.