A ring fragmentation and intramolecular azomethine ylide 1,3-dipolar cycloaddition sequence of reactions was successfully used in the preparation of a known (±)-cycloclavine precursor in good overall yield. Results of efforts to incorporate the tetrasubstituted cyclopropane ring present in cycloclavine are also discussed.

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.

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