Preparation of 1,7- and 3,9-Dideazapurines from 2‑Amino-3-iodo- and 3‑Amino-4-iodopyridines and Activated Acetylenes by Conjugate Addition and Copper-Catalyzed Intramolecular Arylation

The conjugate addition of N-formyl derivatives of 2-amino-3-iodo- and 3-amino-4-iodopyridines to acetylenes activated by sulfone, ester, or ketone groups, followed by intramolecular arylation, affords variously substituted 1,7- and 3,9-dideazapurines. The method employs DMF–water as the solvent and copper­(II) acetate as the catalyst for the cyclization step. Neither added ligands nor the exclusion of oxygen is necessary. The process therefore provides a simple, convenient, and inexpensive route to this biologically interesting class of products.