Bromination and Chlorination of Pyrrole and Some Reactive 1-Substituted Pyrroles

Article abstract of DOI:10.1021/jo00324a005

Monobromination of pyrrole and 1-methyl-, 1-benzyl-, and 1-phenylpyrrole with 1 mol of N-bromosuccinimide in tetrahydrofuran results in the regiospecific formation of the 2-bromopyrroles.A little disubstitution is observed.Similarly, brominations with 2, 3, or 4 mol of NBS form primarily the di-, tri-, and tetrabromopyrroles, respectively.The thermodynamically more stable 3-bromopyrroles are the major monobrominated products observed when bromine is used as the brominating agent due to isomerization of the 2-bromopyrroles with hydrogen bromide.These reaction mixtures are further complicated because of disproportionation reactions.Chlorination with N-chlorosuccinimide gave results similar to those for the bromination with NBS, but the reaction is not as selective.