Development of new sterically hindered chiral phosphoric acids: synthesis and catalytic applications

In the broad field of stereoselective synthesis, Chiral Phosphoric Acids (CPAs) have recently found widespread application in several and crucial chemical transformations, considered powerful tools for the synthesis of pharmaceuticals and natural products. Due to the important applications of chiral phosphoric acids in organic synthesis, in the last few years the design and the synthesis of new chiral phosphoric acids have attracted much attention. A new class of chiral phosphoric acids, with a two-carbon-atom-spacer between the aromatic rings bearing the acidic functional group and a decahydroquinoxaline scaffold derived from the trans-1,2-diaminocyclohexane through a diastereoselective pinacol-type coupling reaction, has been developed. Decahydroquinoxaline-based chiral phosphoric acids have been successfully applied in the model stereoselective Friedel-Crafts addition of indoles to N-tosylimines with good to excellent yields and enantioselectivities.