Palladium(II)-catalyzed asymmetric oxidative cyclization of 2-allylphenols in the presence of copper(II) acetate and molecular oxygen. Study of the catalysis of the Wacker-type oxidation

Article abstract of DOI:10.1021/ja00399a030

The intramolecular oxidative cyclization of trans-2-(2-butenyl)phenol (2) using (+)-(3,2,10-η-pinene)palladium(II) acetate (1) in the pressure of Cu(OAc)₂ and O₂ has been studied in order to gain insight into the catalysis of the Wacker-type oxidation. The main results obtained are as follows: (1) the catalytically active Pd(II) species which is different from complex 1 is formed during the reaction, (2) the chiral pinanyl ligand is retained by the catalyst throughout the reaction, and (3) the catalyst consists of copper and palladium linked with an acetate bridge. These results cannot be accounted for by the conventional Wacker-type catalysis involving the reoxidation of palladium(0). A hydroperoxopalladium(II) species coupled with copper(II) acetate is most likely the active catalyst in the present reaction. A mechanism for the enantioselection is also described in comparison with the results obtained by the oxidative cyclization of cis-2-(2-butenyl)phenol.