Concepts of Heterogeneously Catalyzed Liquid‐Phase Oxidation of Cyclohexene with tert‐Butyl Hydroperoxide, Hydrogen Peroxide and Molecular Oxygen

Abstract

The oxidation of hydrocarbons is of great significance for the chemical industry as it provides access to valuable functionalized chemicals. The oxidation of cyclohexene has raised much interest because it enables the direct synthesis of adipic acid, which is an important building block in polymer chemistry. However, the selective oxidation of cyclohexene is rather challenging due to its two reactive centers so that epoxidation or allylic oxidation may occur leading to a variety of products.Whether the oxidation takes place at the allylic CÀ H bond or at the C=C bond is strongly influenced by the chosen oxidant and catalyst, and different reaction mechanisms can occur. Therefore, this concept article aims at giving a broad overview of the recent advances in the selective cyclohexene oxidation over heterogeneous transition metal-based catalysts using environmentally benign oxidants like tert-butyl hydroperoxide, H 2 O 2 and molecular O 2 .

Tuning Reactivity of Zr-Substituted Keggin Phosphotungstate in Alkene Epoxidation through Balancing H2O2 Activation Pathways: Unusual Effect of Base

“…Catalytic properties of dimer 1 were first evaluated in oxidation of the test alkene substrate CyH with an equimolar amount of hydrogen peroxide (Table ). It is widely accepted that CyH oxidation products strongly depend on the reaction mechanism. ,− The formation of allylic oxidation products, viz., HP, 2-cyclohexene-1-ol (enol), and 2-cyclohexene-1-one (enone), is a clear sign of a homolytic oxidation mechanism, while the selective formation of epoxide and epoxide ring opening product, trans -cyclohexane-1,2-diol (diol), together with the overoxidation product 2-hydroxycyclohexanone (ketol) refer to a heterolytic oxidation mechanism (Scheme S8). In the presence of 1 , CyH conversion reached 36% after 3 h at 50 °C (Table , entry 1).…”

Peroxygenase-Catalyzed Allylic Oxidation Unlocks Telescoped Synthesis of (1S,3R)-3-Hydroxycyclohexanecarbonitrile

“…Data are also shown in Table S1. in particular substituted cyclohexenes, remains challenging 7 and reported chemical strategies include the use of hypervalent iodide reagents, 8 transition metal catalysis, 9,10 or photocatalysis. 11,12 Enzymatic strategies are underdeveloped; 13 examples on few selected substrates include the use of cytochrome P450s and unspecific peroxygenases (UPOs).…”

“…Intermediate 3 not being commercially available, a C–H oxyfunctionalization step is required to introduce the ketone functional group into the commercially available pro-chiral starting material 1 . Regioselective allylic oxidation of alkenes, in particular substituted cyclohexenes, remains challenging and reported chemical strategies include the use of hypervalent iodide reagents, transition metal catalysis, , or photocatalysis. , Enzymatic strategies are underdeveloped; examples on few selected substrates include the use of cytochrome P450s and unspecific peroxygenases (UPOs). , UPOs are well known to selectively catalyze the oxyfunctionalization of ethylbenzene at the benzylic position to the corresponding enantiopure ( R )-1-phenylethanol, and can also further oxidize both enantiomers of 1-phenylethanol to acetophenone, yet remain to be further explored with substituted cyclohexene substrates, in particular with regard to stereoselectivity. , …”

“…Intermediate 3 not being commercially available, a C–H oxyfunctionalization step is required to introduce the ketone functional group into the commercially available pro-chiral starting material 1 . Regioselective allylic oxidation of alkenes, in particular substituted cyclohexenes, remains challenging 7 and reported chemical strategies include the use of hypervalent iodide reagents, 8 transition metal catalysis, 9 , 10 or photocatalysis. 11 , 12 Enzymatic strategies are underdeveloped; 13 examples on few selected substrates include the use of cytochrome P450s and unspecific peroxygenases (UPOs).…”

An Overview of Heterogeneous Transition Metal‐Based Catalysts for Cyclohexene Epoxidation Reaction

“…The epoxidation mechanism is that the transition metal center forms a peroxy complex with the oxidizer, and then transfers an oxygen atom to cyclohexene to form cyclohexane epoxide. However, as Büker says, the comparison of a variety of catalysts clearly shows many exceptions to these basic rules, so that more scientific efforts need to be made to fully understand the underlying mechanisms of cyclohexene oxidation and the precise role of the respective catalyst [9] . Therefore, our work aims to comprehensively review green epoxidation catalysts for cyclohexene and elucidate the detailed epoxidation mechanisms of various transition metal‐based catalysts.…”