New chiral complexes of platinum(II) as catalysts for the enantioselective Baeyer-Villiger oxidation of ketones with hydrogen peroxide:: Dissymmetrization of meso-cyclohexanones

The synthesis and characterization of a number of chiral complexes of the type [(P-P)Pt(mu-OH)](2)(2+) (P-P = (R)-binap, (S,S)-diop, (R,R)-pyrphos, (R,R)-norphos, (R,R)-Me-duphos, (S,S)-bppm) are reported. These are used for the enantioselective Baeyer-Villiger oxidation of substituted meso-cyclohexanones using 35% hydrogen peroxide as oxidant. The reaction is performed at 0 degrees C with moderate yields, showing in some cases ee higher than 50%. Best catalysts are those containing atropoisomeric ligands possessing C-2 symmetry and/or capable of making seven-membered chelate rings with the metal. The results represent the first example of dissymmetrization of achiral cyclohexanones obtained via the Baeyer-Villiger oxidation using a transition metal catalyst.