Utilizing the rapidly synthesized Quinox ligand and commercially available aqueous TBHP, a Wacker-type oxidation has been developed, which efficiently converts the traditionally challenging substrate class of protected allylic alcohols to the corresponding acyloin products. Additionally, the catalytic system is general for several other substrate classes, converting terminal olefins to methyl ketones, with short reaction times. The system is scalable (20 mmol) and can be performed with a reduced catalyst loading of 1 mol%.
View Article and Find Full Text PDFWacker oxidations, the conversion of terminal olefins to methyl ketones with Pd(II) catalysts, have seen widespread use in synthetic applications. Standard synthetic Wacker conditions use catalytic PdCl2 with stoichiometric CuCl under an aerobic atmosphere in a mixed-solvent system of N,N-dimethylformamide and H2O. Though much attention has been directed toward elucidating the rate-determining step and the mechanism of nucleopalladation, the assumption that Cu does not participate in this portion of the catalytic cycle has recently been called into question based on an isolated Pd/Cu bimetallic species and the influence of Cu on product selectivity.
View Article and Find Full Text PDFThe discovery of a direct O2-coupled Wacker oxidation with use of balloon pressure of O2 and low catalyst loading is described. Use of (-)-sparteine as a ligand on Pd prevents olefin isomerization and leads to selective formation of methyl ketones from terminal olefins in good yields. Oxidation of enantiomerically enriched substrates is reported with no observed racemization.
View Article and Find Full Text PDFWe describe the discovery of a new N-heterocyclic carbene-modulated Pd catalyst for the Wacker oxidation that does not require molecular oxygen but instead uses TBHP as a reagent in this oxidation. The catalyst activity and selectivity for the oxidation of styrene derivatives to methyl ketones are among the best reported. Preliminary mechanistic studies of the catalytic system were performed and show that the origin of the carbonyl oxygen is TBHP and that the hydrogens in the product all originate from the starting olefin.
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