Nucleophilic character of alkyl radicals. Part 15. Selective homolytic alkylation of quinoxaline by N-chloro-amines; influence of medium acidity

Abstract

Selective homolytic alkylation of protonated quinoxaline has been achieved by using an alkyl derivative with N-chlorodialkylamine as radical source. The method shows great synthetic potential and can also be used for other heteroaromatic bases. A free-radical chain process involving amine radical cations is suggested to explain the clean reaction. Positional selectivity is strongly affected by the medium acidity, and a correlation between the π-electron density of mono- and di-protonated quinoxaline and the substitution orientation is found, in agreement with the nucleophilic character of the alkyl radicals.