Effect of the leaving group on the reaction of 2-aminopyrroles with electron deficient heteroaromatic azadienes: substitution by addition-elimination versus cycloaddition

When a good leaving group is present in the heteroaromatic azadiene, reaction with 2-aminopyrroles occurs by substitution by addition-elimination instead of cycloaddition. This novel reaction is sensitive to steric effects and takes place in 2-amino-1-methylpyrrole at C-5 and the exo amino group but at C-3 in 2-amino-1-t-butylpyrrole.