Syntheses and Characterization of N-(Indolyl)pyridinium Salts and of Their Ylides

Abstract

3-Methylindole reacts with pyridines in the presence of NBS to give indol-2-yl-pyridinium salts which were converted into their ylides by an anion exchange resin in its hydroxide form. Indol-3- amine was subjected to a nucleophilic ring transformation with pyrylium salts which resulted in the formation of indol-3-yl-pyridinium salts, the 2,4,6-trimethylpyridinium derivative of which proved to be unstable. The 2,4,6-triphenylpyridinium derivate was deprotonated to the corresponding ylide. The isomeric indol-2-yl and indol-3-yl derivatives are cycloimmonium ylides which are members of the compound class of heterocyclic mesomeric betaines (MB). By contrast, the ylide of indol- 2-yl-pyrrolidinium is a cycloammonium ylide. It was prepared by reaction of 3-methylindole with pyrrolidine in the presence of NBS, followed by deprotonation.