Effect of N-chloro Structure and 1-substituent on (σ-substitution (Addition-Elimination) in Pyrroles

1-Methylpyrrole was reacted with a number of different types of N-chloro derivatives, and (σ-substitution was observed only with N-chloroimides. It is proposed that there is a qualitative relationship between the pK_aof the N-chloro precursor and the reaction path. The reaction of 1-substituted pyrroles (CH₃, C₆H₅, C₆H₆CH₂, CH₃CO0, (CH₃)₃C, CH₂—CHCH₂, (C₆H₆)₃C) with N-chlorosuccinimide in CHCl₃/NaHCO₃indicated that (σ-substitution was very sensitive to electronic factors, e.g. no reaction was observed with 1-acetylpyrrole. It was not as sensitive to steric effects, and only with 1-tritylpyrrole was σ-substitution not observed. Only chlorination was observed with pyrrole itself.