Atroposelective [2+2+2] cycloadditions catalyzed by a rhodium(I)–chiral phosphate system
Enantioselective cationic Rh(I)-catalyzed [2+2+2] cycloaddition reactions between diynes and isocyanates relying on the chiral anion strategy have been devised. In the presence of [Rh(cod)Cl]2, 1,4-bis(diphenylphosphino)butane, and the silver phosphate salt Ag(S)–TRIP as the unique source of chirality, axially chiral pyridones were isolated with ees up to 82%. This approach is novel in the field of chiral anion-mediated asymmetric catalysis since atroposelective transformations have so far remained unprecedented. It also proves to be complementary to the classical strategy based on chiral L-type ligands.