Racemic 1,2-diols and a-hydroxy carbonyl compounds can be asymmetrically benzoylated in a kinetic resolution in the presence of various Cu(II)-aza(bisoxazoline) catalysts. A novel bisbenzyl-substituted aza(bisoxazoline) ligand proved to be especially effective when immobilized on MeOPEG(5000), giving from 91 to >= 99% ee in 37-49% yield for each of five sequential reactions.
Asymmetric Catalytic Insertion of α-Diazo Carbonyl Compounds into O–H Bonds of Carboxylic Acids
An efficientenantioselectiveinsertion of α-diazoesters and α-diazoketones into O–H bonds of carboxylic acids was realized by the use of Rh2(OAc)4 and a chiral guanidine. Optically active α-acyloxy carbonyl compounds were generated under mild reaction conditions in high yields (up to 99%) and good enantioselectivities (up to 97.5:2.5 er).