Palladium-catalyzed Oxidative Reaction Research Articles

Efficient Palladium-Catalyzed Aerobic Oxidative Carbocyclization to Seven-Membered Heterocycles.

The use of molecular oxygen in palladium‐catalyzed oxidation reactions is highly widespread in organic chemistry. However, the direct reoxidation of palladium by O2 is often kinetically unfavored, thus leading the deactivation of the palladium catalyst during the catalytic cycle. In the present work, we report a highly selective palladium‐catalyzed carbocyclization of bisallenes to seven‐membered heterocycles under atmospheric pressure of O2. The use of a homogenous hybrid catalyst (Co(salophen)‐HQ, HQ=hydroquinone) significantly promotes efficient electron transfer between the palladium catalyst and O2 through a low‐energy pathway. This aerobic oxidative transformation shows broad substrate scope and functional group compatibility and allowed the preparation of O‐containing seven‐membered rings in good yields in most cases.

Palladium-catalyzed oxidative synthesis of highly functionalized ortholactones.

A palladium-catalyzed oxidative reaction is reported which converts dihydropyrans to their corresponding ortholactone. The products are formed in good to excellent yields with a very high level of chemoselectivity and functional group tolerance. Mechanistic studies confirm that the reaction proceeds by a Wacker-type mechanism.

Palladium-catalyzed Oxidation of Benzyl Ketones to Synthesis of α-Acetoxy Ketones Using Molecular Oxygen

Abstract An efficient procedure for the preparation of α-acetoxy ketone derivatives by palladium-catalyzed oxidation reactions employing molecular oxygen as the sole oxidant has been reported. A variety of benzyl ketones were used to investigate the scope of the reactions.

Similarities between the reactions of dioxygen and alkenes with palladium(0): Relevance to the use of benzoquinone and molecular oxygen as stoichiometric oxidants in palladium-catalyzed oxidation reactions

Bathocuproine-coordinated palladium(0) complexes, (bc)Pd 0(alkene) (bc = 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) undergo facile oxygenation in the presence of molecular oxygen to produce the η 2-peroxopalladium(II) complex, (bc)Pd II(O 2). The same Pd(0)-alkene complexes undergo self- and cross-exchange reactions with exogenous alkenes. Mechanistic studies highlight distinct similarities between the oxygenation and alkene-substitution reactions: kinetic studies reveal that both reactions proceed via an associative addition/substitution pathway, and electronic effects reveal that the transition states for both reactions feature removal of electron density from (i.e., oxidation of) the palladium(0) center. These results have important implications for the reactivity of dioxygen and benzoquinone (an electron-deficient alkene) as stoichiometric oxidants in palladium-catalyzed oxidation reactions.