Diversity-oriented silver(i)-mediated synthesis of spiro-2-aminoimidazoles

A diversity-oriented protocol giving access to a novel class of spiro-cyclic guanidine derivatives is described. The copper(I)-catalyzed, three-component coupling of a ketone, an alkyne and a primary amine (KA ²-coupling) provides the required secondary propargylamines and assures the generation of diversity. The key step of the protocol, a silver(I)-mediated tandem guanylation of secondary propargylamines followed by an intramolecular heterocyclization, provides the target bis-Boc-protected-2- iminoimidazolines spiro-fused with a five-, six- or seven-membered (heterocyclic) ring, which could, in most cases, be further deprotected to the spiro-2-aminoimidazoles.