PLATINUM-CATALYZED OXIDATIONS WITH HYDROGEN-PEROXIDE - ENANTIOSPECIFIC BAEYER-VILLIGER OXIDATION OF CYCLIC-KETONES

The Baeyer-Villiger oxidation of some cyclic ketones as a potential entry to naturally occurring lactones is reported in the presence of a variety of platinum(II) complexes as catalysts. The reaction is accomplished using hydrogen peroxide as oxidant and is tested in a discontinuous and semicontinuous fashion. The stereochemistry of the catalyzed transformation has been determined, and it is found that the reaction proceeds with retention of configuration at the migrating carbon atom. Chiral catalysts of the type [(P-P*)Pt(CF3)(solv)](+) and (P-P*)Pt(2-van) (P-P* = various chiral diphosphines; 2-van = the dianion of 2-vanillin) have been synthesized and characterized. While the mechanism of action of the former complexes is already known, the latter require 1 equiv of HClO4 to become catalytically active. This reaction has been investigated synthetically and spectroscopically by P-31{H-1} NMR and IR and results in the formation of a new cationic Pt-carbonyl species. The asymmetric Baeyer-Villiger oxidation of a variety of racemic mixtures of chiral ketones results in a kinetic resolution leading to chiral lactones with ee up to 58%.