New sildenafil analogues containing an ether ring fused into the phenyl moiety, 6a–d and 7a– d, were efficiently synthesized from the readily available starting materials, 1a–d and 2, in five steps. Ab initio calculations indicated that introduction of a cyclic ether to the phenyl group might enhance the co-planarity of the molecule. The torsional angles were calculated to be 2− 3° for the 5-membered cyclic ether derivatives, 6a, 6c, 7a, and 7c, and 12− 16° for ...
