Efficient switching from the 2,3′- to 2,2′-bipyrrole scaffold via the recyclization of 1-(benzoylmethylanilino)-3-imino-3 H -2-cyanopyrrolizines: Crucial effect of the DBU organic superbase

The recyclization of readily available 1-(benzoylmethylanilino)-3-imino-3H-2-cyanopyrrolizines using the DBU organic superbase, unexpectedly gave 2,2′-bipyrroles with amino, keto and cyano functional groups on one of the pyrrole rings in 83–94% yield. Previously, using the KOH/DMSO system, this recyclization led to 2,3′-bipyrroles in low yields (12–26%). This selective switching was explained by sterically hindered access for the intermediate carbanion to the 1-position of the pyrrolizine ring due to the large size of the accompanying DBU countercation. The new methodology opens an efficient route to pharmaceutically and synthetically useful densely functionalized 2,2′-bipyrroles.