Highly Enantioselective Oxidation of Spirocyclic Hydrocarbons by Bioinspired Manganese Catalysts and Hydrogen Peroxide

Abstract

Bioinspired manganese complexes have emerged as attractive catalysts for a number of selective oxidation reactions over the past several decades. In the present study, we report the enantioselective oxidation of spirocyclic compounds with manganese complexes bearing tetradentate N4 ligands as catalysts and aqueous H2O2 as a terminal oxidant under mild conditions; spirocyclic tetralone (1a) and its derivatives bearing electron-donating and -withdrawing substituents are converted to their corresponding chiral spirocyclic β,β′-diketones with high yields and enantioselectivities. Spirocyclic indanones are also converted to the β,β′-spirobiindanones with high enantioselectivities. Indeed, the reaction expands the diversity of chiral spirocyclic diketones via a late-stage oxidative process. In addition, it is of importance to note that the catalytic reaction can be easily scaled up and the chiral spirocyclic β,β′-diketones can be transformed into diol products. In mechanistic studies, we have shown that (1) ketones were yielded as products via the initial formation of alcohols, followed by the further oxidation of the alcohols to ketones, (2) hydrogen atom (H atom) abstraction from the methylene C–H bonds of 1a by a putative Mn­(V)-oxo intermediate was proposed to be the rate-determining step, and (3) the C–H bond hydroxylation of 1a by the Mn­(V)-oxo species was proposed to occur via oxygen rebound mechanism. On the basis of these results, we have proposed a plausible mechanism for the selective C–H bond oxidation of hydrocarbons by bioinspired manganese catalysts and hydrogen peroxide.

Catalytic enantioselective C(sp3)–H functionalization involving radical intermediates

“…With the synergistic cooperation of a sterically demanding tetradentate Mn catalyst analogous to 2 and an oxidatively robust alkanoic acid, the reaction furnishes the corresponding chiral ketone with excellent regioselectivity and enantioselectivity. Similarly, Nam, Sun, and coworkers have employed a structurally related Mn catalyst for enantiotopos-selective benzylic C( sp 3 )–H oxidation of spirocyclic ketone 36 .…”

Activation and Deactivation Strategies Promoted by Medium Effects for Selective Aliphatic C−H Bond Functionalization

“…[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Ther eagents that are typically involved in these processes include heteroatomcentered radicals and radical ions,p hotoexcited species and photocatalysts (carbonyl compounds,polyoxometalates), biocatalysts (cytochrome P450 and oxygenases) and bioinspired catalysts,a swell as closed-shell species such as dioxiranes. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Ther eagents that are typically involved in these processes include heteroatomcentered radicals and radical ions,p hotoexcited species and photocatalysts (carbonyl compounds,polyoxometalates), biocatalysts (cytochrome P450 and oxygenases) and bioinspired catalysts,a swell as closed-shell species such as dioxiranes.…”

“…Among the available methods for the site-selective functionalization of aliphatic CÀHb onds,t hose based on hydrogen atom transfer (HAT) to radical or radical-like species play an important role. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Ther eagents that are typically involved in these processes include heteroatomcentered radicals and radical ions,p hotoexcited species and photocatalysts (carbonyl compounds,polyoxometalates), biocatalysts (cytochrome P450 and oxygenases) and bioinspired catalysts,a swell as closed-shell species such as dioxiranes.…”

Pd Nanoparticles‐Polyethylenemine‐Lipase Bionanohybrids as Heterogeneous Catalysts for Selective Oxidation of Aromatic Alcohols

“…However, many of them are synthesized using expensive and toxic oxidants, base additives or high experimental temperatures (80 °C) . Recently the application of more sustainable oxidants such as oxygen or hydrogen peroxide has been successfully applied . However, for an economically and environmental‐industrial application process, the required high oxygen pressure increases the system‘s complexity.…”