Manganese‐Catalyzed Selective Oxidation of Aliphatic CH groups and Secondary Alcohols to Ketones with Hydrogen Peroxide

Abstract

An efficient and simple method for selective oxidation of secondary alcohols and oxidation of alkanes to ketones is reported. An in situ prepared catalyst is employed based on manganese(II) salts, pyridine-2-carboxylic acid, and butanedione, which provides good-to-excellent conversions and yields with high turnover numbers (up to 10 000) with H2 O2 as oxidant at ambient temperatures. In substrates bearing multiple alcohol groups, secondary alcohols are converted to ketones selectively and, in general, benzyl C-H oxidation proceeds in preference to aliphatic C-H oxidation.

Origins of Catalyst Inhibition in the Manganese‐Catalysed Oxidation of Lignin Model Compounds with H2O2

“…The oxidation of 1‐phenyl‐1,2‐ethanediol and 1 with H 2 O 2 was studied here by using conditions optimized earlier for the oxidation of secondary aliphatic and benzylic alcohols . With the in situ‐prepared manganese catalyst (Scheme ), 1‐phenyl‐1,2‐ethanediol underwent 60 % conversion to the corresponding α‐hydroxyketone, as reported previously .…”

“…Recently, we reported a manganese(II) catalyst prepared in situ with pyridine‐2‐carboxylic acid (PCA) and sub‐stoichiometric ketones for the oxidation with H 2 O 2 of a broad range of organic compounds such as alkanes, olefins, aliphatic and benzylic alcohols under ambient conditions with high turnover numbers (up to 300 000 for the epoxidation of electron‐rich alkenes) and low catalyst loadings (Scheme ) . The simplicity of the catalyst in preparation and, importantly, its wide solvent scope make it a potential candidate for large‐scale application.…”

“…The simplicity of the catalyst in preparation and, importantly, its wide solvent scope make it a potential candidate for large‐scale application. In particular, the good conversion shown in the oxidation of secondary benzylic alcohols, such as p ‐X‐1‐phenylethanol (X=H, Br, OCH 3 ) and aromatic vicinal diols to ketones, even if the benzylic alcohol positions were protected as ethers, encouraged us to consider the potential of this Mn system in catalytic lignin degradation, in particular for attack at the β‐O‐4 linkage …”

Redox‐State Dependent Ligand Exchange in Manganese‐Based Oxidation Catalysis

“…The manganese pyridine-2-carboxylic acid system subsequently developed by Saisaha [167] and Dong et al [168] for the cis-dihydroxylation and epoxidation of alkenes, as well as alcohol and alkane oxidation, [169] presented a considerable challenge with regard to mechanistic studies because of the turnover frequencies (30 s -1 ) and turnover numbers Scheme 7. Oxidative decomposition of polypyridyl ligands to pyridine-2-carboxylic acid (PCA), which was found to be the ligand responsible for the manganese-based oxidation catalysis observed with H 2 O 2 and alkenes.…”

Synthetic utility of metal catalyzed hydrogen peroxide oxidation of C-H, C-C and C=C bonds in alkanes, arenes and alkenes: Recent advances

“…It provides good-to-excellent conversions of benzyl and alkyl groups as well as secondary alcohols with high turnover numbers (up to 10 000). 85 The triosmium dodecacarbonyl cluster Os 3 (CO) 12 catalyzes oxidation of linear (n-heptane) and cyclic alkanes (cyclohexane, cyclooctane, methylcyclohexane, cis-and trans-1,2-dimethylcyclohexanes) to the corresponding cycloalkyl hydroperoxides by hydrogen peroxide in acetonitrile. Addition of pyridine leads to an acceleration of the process.…”