Modular furanoside diphosphite ligands for Pd-catalyzed asymmetric allylic substitution reactions:: Scope and limitations

We have synthesized a library of furanoside diphosphite ligands for the Pd-catalyzed allylic substitution reactions of acyclic and cyclic allylic esters. The library has been designed to rapidly screen the ligands to uncover their important structural features and to determine the scope of diphosphite ligands in these catalytic reactions. After the systematic variation of the sugar backbone, the substituent at C-5 and the phosphite moieties, the diphosphite ligand 4c was found to be optimal in the Pd-catalyzed asymmetric allylic substitution of hindered (S1) and unhindered (S2-S5) substrates, yielding high activities [TOFs up to > 3000 mol x (mol x h) (-1)] and enantioselectivities (ees up to 99%). In addition, the screening of the library enabled us to find other suitable ligands for hindered disubstituted linear substrate S1 (ligands 1b-d, g and 4b, d, g) and for unhindered cyclic substrates S3-S5 (ligands 6c and 7c).