Stereoselective synthesis of a tricyclic guanidinium model of cylindrospermopsin

An 11-step enantioselective synthesis of the A-ring of cylindrospermopsin is described using an intramolecular conjugate addition as the key step to forming the piperidine ring. Further elaboration generates a tricyclic guanidine via a sequential double displacement strategy as a model for the cylindrospermopsin guanidinium core.