Asymmetric Catalytic Insertion of α-Diazo Carbonyl Compounds into O–H Bonds of Carboxylic Acids

An efficient enantioselective insertion 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).