Vinyl pyrrolidines tethered to isothioureas are activated to the corresponding carbodiimides with AgOTf and Et 3 N. Intramolecular addition of the vinyl pyrrolidine amine to the carbodiimide followed by a 1,3-diaza-Claisen rearrangement affords [9,5]-and [9,6]-bicyclic guanidines depending on the tether length in good to excellent yields. Density functional theory calculations reveal that the pathway involving intramolecular addition of the amine to carbodiimide to afford a zwitterionic intermediate followed by the zwitterionic 1,3-diaza-Claisen rearrangement was consistently a higher energy pathway than the path involving protonation of the zwitterionic intermediate followed by the cationic 1,3-diaza-Claisen rearrangement.