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.
Original language | English |
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Pages (from-to) | 2479-2487 |
Number of pages | 9 |
Journal | ACS Catalysis |
Volume | 8 |
Issue number | 3 |
DOIs | |
State | Published - 2 Mar 2018 |
Bibliographical note
Funding Information:We acknowledge financial support of this work from the National Natural Science Foundation of China (21473226 and 21773273 to W.S.) and the NRF of Korea through CRI (NRF-2012R1A3A2048842 to W.N.) and GRL (NRF-2010-00353 to W.N.).
Publisher Copyright:
© 2018 American Chemical Society.
Keywords
- asymmetric oxidation
- C-H oxidation
- hydrogen peroxide
- manganese catalyst
- manganese-oxo
- mechanism