Enhanced Catalyst Activity and Enantioselectivity with Chirality-Switchable Polymer Ligand PQXphos in Pd-Catalyzed Asymmetric Silaborative Cleavage of meso-Methylenecyclopropanes

The poly(quinoxaline-2,3-diyl)-based helically chiral phosphine ligands PQXphos exhibited high enantioselectivities up to 97% ee in palladium-catalyzed desymmetrization of meso-1,2-dialkylsubstituted-3-methylenecyclopropanes through silaborative cleavage of the C C bond. The observed enantioselectivities were higher than those obtained with 2-diarylphosphino-1,1'-binaphthyl in our original report. Remarkable rate enhancement was also observed with a series of PQXphos in comparison with the corresponding low-molecular weight ligands.