Asymmetric epoxidation using aqueous hydrogen peroxide as oxidant: bio-inspired construction of pentacoordinated Mn–salen complexes and their catalysis

(Salen)Mn(III) Catalyzed Asymmetric Epoxidation Reactions by Hydrogen Peroxide in Water: A Green Protocol

“…In fact, the heterolytic O–O bond cleavage yielding the oxene, (salen)Mn(V)=O, which is the real oxidant species [ 31 , 32 ], is favoured by these bases [ 33 , 34 , 35 , 36 ]. However, in all these studies, the main solvent is not water but an organic solvent (e.g., CH 2 Cl 2 /CH 3 OH 1/1, CH 2 Cl 2 /DMF 1/3 and CH 2 Cl 2 ) to prevent potential solubility problems [ 24 , 37 , 38 ]. An environmentally friendly protocol for salen catalyzed enantioselective epoxidation reactions would envisage hydrogen peroxide as oxidant and water as a reaction medium.…”

Sustainability Trends in Homogeneous Catalytic Oxidations

“…Subsequently, this led to the direct covalent connection of a nitrogen-based ligand to the salen scaffold leading to pentadentate ligands bearing atropoisomeric binaphthyl moieties (Scheme 23.3). 9 In particular, the complex containing a methylimidazole residue as a fifth coordinating moiety turned out to be the best catalyst towards electron-rich alkene substrates belonging to the chromene or styrene families, with excellent yields and extremely high enantiomeric excesses. More recently, other nitrogen-based chiral ligands started to be employed for the development of Mn(II) epoxidation catalysts.…”

Asymmetric Oxidation with Hydrogen Peroxide, an Effective and Versatile Oxidant

“…On the basis of structural analysis of the Mn-salen complexes, Shitama and Katsuki designed a new type of Mn-salen complex 4 bearing a (4-imidazoyl)methyl substituent at the ethylene part and achieved highly enantioselective epoxidation (up to 98% ee) using 30% hydrogen peroxide (Scheme 3.5) [26]. However, the epoxidation of acyclic cis-olefins is nonstereospecific.…”