Nucleophilic substitution in the side chain of five-membered heterocycles. Part 4. Reaction kinetics of selenophen compounds

Abstract

The polarity σ* constant of the selenophen ring has been obtained from the rates of acid- and base-catalysed hydrolysis of ethyl selenophen-2-carboxylate, following the Taft procedure. Kinetics of the reaction of selenophen-2-sulphonyl chloride and 2-chloromethylselenophen with aniline, and of selenophen-2-carbaldehyde with aniline and with a phosphorus ylide have been investigated. Comparison between the reactivities of selenophen and thiophen compounds confirms the similarity of the electrical effects of both heterocycles. The results, together with previous data for furan, thiophen, pyrrole, and benzene derivatives, are rationalized by correlation analysis with polar or electrophilic constants of heterocycles, depending on the side-chain electron demand.