Synthesis of chiral 4, 4′-disubstituted 1, 1′-spirobiindane-7, 7′-diols and related phosphoramidites: the substituent effect of SIPHOS ligands in Rh-catalyzed …
Three chiral 4, 4′-substituted 1, 1′-spirobiindane-7, 7′-diols and related monodentate spiro phosphoramidite ligands have been readily synthesized from enantiomerically pure 1, 1′-spirobiindane-7, 7′-diol. Excellent enantioselectivities were obtained with these new ligands in the rhodium-catalyzed asymmetric hydrogenation of dehydroamino acid derivatives and enamides. Comparing SIPHOS, ligands 4, 4′-dibromo-SIPHOS and 4, 4 ...