Cyclopenta[<i>b</i>]pyrroles from Triazines: Synthetic and Mechanistic Studies

The pyrrolidine-mediated reactions of 3,5-disubstituted 1,2,4-triazines with cyclobutanone lead to cyclopenta[b]pyrroles, which can be derivatized into hydrazones and oximes. The cyclopenta[b]pyrrole ring system likely arises through a tandem [4 + 2] cycloaddition/cycloreversion/ring rearrangement reaction. In contrast, 3,6-disubstituted 1,2,4-triazines undergo a simple nucleophilic 1,4-addition with cyclobutanone to give 1:1 adducts.