Synthesis of Purines and Other Fused Imidazoles from Acyclic Amidines and Guanidines

[reaction: see text] Purines, xanthines, and other fused imidazoles can be prepared from amidines or guanidines, with retrosynthetic disconnection at the ring fusion. Ring closure proceeds using Cu(I), with no special ligands required. The method allows for easy modification of the heterocyclic nucleus and is tolerant of functionality pendant to the ring system.