Mn-PYBP Catalyzed Inactivated C(sp~3)-H Bond Oxidation

The C(sp3)-H bond oxidation has always been a very challenging research.Because the carbon-hydrogen bond has relatively high bond energy,and the carbon-hydrogen bond is the basic unit of organic molecules,this makes it very difficult to achieve selective carbon-hydrogen bond oxidation.The selective oxidation of C(sp3)-H bonds plays an extremely important role in synthetic chemistry,especially in the synthesis of large chemical products,fine chemicals,drug molecules,and the later modification of drug molecules.Due to the huge demands of these industries,the selective oxidation of carbon-hydrogen bonds has become an urgent problem to be solved.The C(sp3)-H bond oxidation is mainly divided into the oxidation of activated carbon-hydrogen bonds and the oxidation of non-activated carbon-hydrogen bonds.Regarding the oxidation of activated carbon-hydrogen bonds(benzyl,allyl,oxygen,nitrogen and other heteroatoms a site),mainly including oxidation catalyzed by heme metal catalysts(metal porphyrin complex)and non-heme metal catalysts(Salen-Mn,manganese),and also photocatalytic oxidation,etc.Regarding the oxidation of non-activated carbon-hydrogen bonds,there are mainly oxidation catalyzed by heme metal catalysts and non-heme metal catalysts(Salen-Mn,ruthenium,iron,manganese),and also electrochemical oxidation,etc.At present,there are many problems in the oxidation of non-activated carbon-hydrogen bonds in terms of reactivity,chemoselectivity,and functional group compatibility,etc.Therefore,it is very important to develop a new high-efficiency catalyst to achieve the selective oxidation of non-activated carbon-hydrogen bonds.Importantly,this can solve many practical problems in organic synthesis.In this paper,we used a new type of tetradentate nitrogen-containing manganese[(R,R')-Mn-TIPSPYBP]with bipiperidine-bipyridine as the framework is developed as a catalyst,green and economical H2O2 as an oxidant,and carboxylic acid as an additive to realize the selective oxidation of non-activated carbon-hydrogen bonds.The catalytic reaction in this paper uses 1-(4-chlorophenyl)cyclopentane-1-carboxylic acid methyl ester as a model substrate.Through the screening of catalysts,solvents,oxidant equivalents and additives,the optimal conditions for the reaction are obtained.And we ued the optimal conditions to expand a series of substrates,and realized the selective oxidation of cycloalkane carboxylic acid esters,cyclic and chain amines protected by phthalic anhydride,benzoates,unprotected cyclic amines and other types of substrates.In addition,this catalytic system can also perform selective carbon-hydrogen bond oxidation of complex molecules with good yields.At the same time,this paper also explores the mechanism of catalytic oxidation.In a word,this paper developed a new type of tetradentate nitrogen-containing manganese catalytic system,with mild conditions,wide substrate applicability,and realized efficient,convenient and green selective oxidation of non-activated carbon-hydrogen bonds.