PALLADIUM-CATALYZED ALLYLIC ACETOXYLATION OF OLEFINS USING HYDROGEN-PEROXIDE AS OXIDANT

A new and efficient system for the allylic acetoxylation of olefins has been developed, which consists of a palladium (II) catalyst and hydrogen peroxide as oxidant in acetic acid. The acetoxylation reaction competes with the epoxidation by the peracetic acid generated in situ in this system. Increase of the concentration of palladium catalyst and addition of benzoquinone (BQ), enhance the acetoxylation considerably. For the Pd(OAc)(2)-BQ-H2O2 system, more than 1000 turnover number could be achieved in the acetoxylation of cyclohexene. Most internal and cyclic olefins tested gave the corresponding allylic acetates in fair to high yields. 1,3-Cyclohexadiene gave 1,4-diacetoxy-cyclohex-2-ene while 1,5-hexadiene afforded 3-acetoxy-methylenecyclopentane; 1,7-octadiene produced 1-octen-7-one and octan-2,7-dione. Terminal olefins gave methyl ketones in good yield with high turnover number both in the presence and absence of BQ. Possible mechanisms and involvement of palladium peroxidic species in both the catalytic acetoxylation and ketonization of olefins are discussed.