Alkynylbenzaldehyde cyclizations catalyzed by Ag(I) complexes of chiral pyridine containing macroclyclic ligands (Pc-L*)

The tandem acetalization/cycloisomerization of ortho-alkynylbenzaldehydes, originally reported by Yamamoto using Pd(OAc)2 as a catalyst, gives 1H-isochromene derivatives that can have useful medicinal properties. Although several related tandem processes using different nucleophiles are known, no enantioselective version of this reaction has appeared until the very recent report by Slaughter and coworkers. Their study, published after we started our investigations, is based on the use of chiral gold(I) acyclic diaminocarbene complexes as catalysts in the presence of LiNTf2 (Tf=trifluoromethanesulfonyl) as a necessary additive to achieve useful activity. Recent studies in our research group demonstrated the efficacy of Cu(I) complexes derived from novel macrocyclic ligands containing a pyridine ring (Pc-L*) in the cyclopropanation reaction. The excellent results obtained up to now with copper prompted us to verify the application of silver(I) complexes of these ligands in catalysis. We herein report the synthesis of the new Ag(I) macrocyclic complexes, and their catalytic activity in the synthesis of oxygenated heterocycles by addition/cycloisomerization reactions of alcohols and ortho-alkynylbenzaldehydes.