Synthesis of pyrano[2,3-f]chromen-2-ones vs. pyrano[3,2-g]chromen-2-ones through site controlled gold-catalyzed annulations

Abstract

Regioselective access to 10-substituted-2H,8H-pyrano[2,3-f]chromen-2-ones through the gold-catalyzed intramolecular hydroarylation of readily available 7-(prop-2-yn-1-yloxy)-2H-chromen-2-one derivatives at their C-8 congested position was investigated by tuning the electronic and steric properties of the ligand on the gold complex. On the other hand, the combination of the JohnPhosAu(MeCN)SbF₆ catalyzed intramolecular hydroarylation of 8-iodo-7-(prop-2-yn-1-yloxy)-2H-chromen-2-one derivatives followed by selective palladium/formate C–I reduction allows for the exclusive formation of 2H,8H-pyrano[3,2-g]chromen-2-one regioisomers. The development of these two protocols provides versatile synthetic tools required for exploring the biological activities of these new pyranocoumarin derivatives.