Synthesis of chiral biphenol-based diphosphonite ligands and their application in palladium-catalyzed intermolecular asymmetric allylic amination reactions

A library of new 2,2'-bis(diphenylphosphinoyloxy)-1,1'-binaphthyl (binapo)-type chiral diphosphonite ligands was designed and synthesized based on chiral 3,3',5,5',6,6'-hexasubstituted biphenols. These bop ligands have exhibited excellent efficiency in a palladium-catalyzed intermolecular allylic amination reaction, which provides a key intermediate for the total synthesis of Strychnos indole alkaloids with enantiopurities of up to 96% ee. A library of chiral diphosphonite (bop) ligands was synthesized based on chiral hexasubstituted biphenols with fine-tuning capability. Their application for the synthesis of a key intermediate to indole alkaloids through a palladium-catalyzed intermolecular asymmetric allylic amination is reported (TBS=tert-butyldimethylsilyl, TIPS=triisopropylsilyl, dba=dibenzylideneacetone).