Catalytic Oxidative Cleavage Reactions of Arylalkenes by tert-Butyl Hydroperoxide – A Mechanistic Assessment

Abstract

Oxidative cleavage reactions of arylalkenes by tert-butyl hydroperoxide that occur by free radical processes provide access to carboxylic acid or ketone products. However, the pathway to these cleavage products is complex, initiated by regioselective oxygen radical addition to the carbon–carbon double bond. Subsequent reactions of the initially formed benzyl radical lead eventually to carbon–carbon cleavage. Thorough investigations of these reactions have identified numerous reaction intermediates that are on the pathways to final product formation, and they have identified a new synthetic methodology for the synthesis of peroxy radical addition-induced hydroperoxide formation.

Oxidative cleavage of C–C double bond in cinnamic acids with hydrogen peroxide catalysed by vanadium(v) oxide

“…Alternatively, many other oxidants have been investigated to achieve selective oxidative cleavage of double bonds, e.g. OsO 4 /NaIO 4 (Lemieux-Johnson reaction) 8,9 , Oxone 10,11 , m-CPBA 12 , t-BuOOH [13][14][15] , KMnO 4 16,17 … These methods also have some disadvantages, such as toxicity, high price, and generation of stoichiometric oxidant as waste. Using biobased molecules as feedstock demands the use of environmentally friendly oxidants such as oxygen and hydrogen peroxide.…”

Application of α-Aminoalkyl Radicals as Reaction Activators

“…23 Diverse -peroxy--substituted ethylbenzene products were synthesized in 52-97% yield. The reaction is initiated by Cu(I)-catalyzed decomposition of tert-butyl hydroperoxide (TBHP), 24 delivering the tert-butoxy radical and Cu(II) species B, which is proposed to be in equilibrium with ICu-OO t Bu (C). The highly reactive tert-butoxy radical reacts with another molecule of TBHP to provide the more stable and highly selective tert-butylperoxy radical, which undergoes a selective HAT process at the C-H bond  to nitrogen on diisopropylethylamine (DIPEA) affording the key -aminoalkyl radical intermediate G. Selective abstraction of a halogen atom by the -aminoalkyl radical G from R 2 -X generates the R 2 radical and iminium salt H. Addition of R 2• to the C=C bond then produces benzyl radical E. Among the three possible pathways for formation of the final products, the authors suggested that radical recombination and subsequent reductive elimination (Path a) is more favorable according to control experiments and DFT calculations.…”

1,2-Dibutoxyethane-Promoted Oxidative Cleavage of Olefins into Carboxylic Acids Using O2 Under Clean Conditions

“…Several methods have been developed in the oxygenation of CC bonds with O 2 or air as the sole oxidant. − However, most of these developed oxidation systems could only chemoselectively transform into the corresponding alcohols, , aldehydes, or ketones, − possibly due to the triplet-ground-state of O 2 , which generates a high kinetic barrier to oxidation and results in inefficient utilization of oxygen. , To overcome these drawbacks, several approaches have been reported, such as photocatalyst-promoted, transition-metal catalyzed, and additive-promoted oxidation of alkenes to carboxylic acids using O 2 as the oxygen source. For example, Hirashima et al developed a method for the CBr 4 -catalyzed oxidative cleavage of alkenes to produce carboxylic acids with O 2 under aerobic photoirradiation conditions (Scheme a) .…”

“…In 2016, Urgoitia reported a NiBr 2 /azole ligand system-assisted one-pot synthesis of carboxylic acids via oxidation of CC with O 2 (Scheme b) . Recently, Doyle et al revealed a TBHP-promoted synthetic methodology to prepare carboxylic acid from aryl alkenes with O 2 as the terminal oxidant (Scheme c) . Although the above methods demonstrate significant advantages, from a practical and environmentally friendly angle of vision, they need an external catalyst, an additive, or illumination to promote the reaction, which can cause environmental problems and increase the cost.…”