Nickel-catalyzed remote and proximal Wacker-type oxidation

Abstract

Wacker oxidation chemistry is widely applied to oxidation of olefins to carbonyls in the synthesis of pharmaceuticals, natural products, and commodity chemicals. However, in this chemistry efficient oxidation of internal olefins and highly selective oxidation of unbiased internal olefins without reliance upon suitable coordinating groups have remained significant challenges. Here we report a nickel-catalyzed remote Wacker-type oxidation where reactions occur at remote and less-reactive sp 3 C-H sites in the presence of a priori more reactive ones through a chain-walking mechanism with excellent regio-and chemo-selectivity. This transformation has attractive features including the use of ambient air as the sole oxidant, naturally-abundant nickel as the catalyst, and polymethylhydrosiloxane as the hydride source at room temperature, allowing for effective oxidation of challenging olefins. Notably, this approach enables direct access to a broad array of complex, medicinally relevant molecules from structurally complex substrates and chemical feedstocks.

Iron‐Catalyzed Wacker‐type Oxidation of Olefins at Room Temperature with 1,3‐Diketones or Neocuproine as Ligands**

“…This catalytic system is generally less efficient for the oxidation of internal alkenes and electron-deficient olefins. Despite recent progress to overcome these limitations, [9] the search for inexpensive alternatives has led to the development of earth-abundant first-row transition-metal catalysis for this transformation with application of iron, [10] cobalt, [11] or nickel [12] compounds as catalysts.Han et al described aWacker-type oxidation of alkenes to ketones in ethanol at 80 8 8C using iron(II) chloride as catalyst, polymethylhydrosiloxane [*] Dr.F.Puls, P. Linke, Prof. Dr.H . an open access article under the terms of the Creative Commons Attribution Non-Commercial NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is noncommerciala nd no modifications or adaptations are made.…”

Formate-driven catalysis and mechanism of an iridium–copper complex for selective aerobic oxidation of aromatic olefins in water

“…The metal-alkylperoxido species formed by the O 2 insertion into the metal-alkyl bond has been previously reported [49][50] and was also proposed as a reaction intermediate in Wacker-type oxidations of olefins. 31,32 The DFT-optimized structure and the electronic properties of Ir(OOEtBnS)-Cu are shown in Fig. S13 and Table S4.…”

“…30 Metal-hydride (M-H) species have been receiving increasing attention in the Wacker-type oxidations because, by using these species, in contrast to the palladium case, the catalysis exhibits unique behaviour and proceeds without the need of an additional electron mediator. 31,32 This approach, however, is limited by the difficulty of generating M-H species by reactive hydride sources, which are reductants not usually adopted in an aqueous solutions for oxidation reactions. Thus, a method that allows us to generate M-H species in aqueous solution that allows us to build a hydrophobic environment suitable for selective oxidations of organic substrates would be highly desirable.…”

Tackling Remote sp3 C−H Functionalization via Ni‐Catalyzed “chain‐walking” Reactions

“…At present, these protocols primarily rely on Pd catalysts, invariably forging a C−O bond at the prefunctionalized alkene terminus. Recently, Han reported a rather intriguing Ni‐catalyzed Wacker oxidation‐type protocol that results in the functionalization of remote benzylic sites via “chain‐walking”, thus allowing to convert olefins substituted with aryl groups into the corresponding alkyl aryl ketones (Scheme ) . As for other Ni‐catalyzed “chain‐walking” reactions, the nature of the ligand was critical for success, with nitrogen‐containing ligands containing substituents adjacent to the nitrogen atom providing the best results ( L12 ).…”