There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Ru-, Rh-, and Pd-Catalyzed C-C Bond Formation Involving C-H Activation and Addition on Unsaturated Substrates: Reactions and Mechanistic Aspects

Catalytic C–H activation has emerged as a powerful tool for sustainable syntheses. In the recent years, notable success was achieved with the development of cobalt-catalyzed C–H functionalizations with either in situ generated or single-component cobalt-complexes under mild reaction conditions. Herein, recent progress in the field of organometallic cobalt-catalyzed C–H activation is reviewed until November 2015.

Cobalt-Catalyzed C―H Activation

The development of new methods for the direct functionalization of unactivated C–H bonds is ushering in a paradigm shift in the field of retrosynthetic analysis. In particular, the catalytic enantioselective functionalization of C–H bonds represents a highly atom- and step-economic approach toward the generation of structural complexity. However, as a result of their ubiquity and low reactivity, controlling both the chemo- and stereoselectivity of such processes constitutes a significant challenge. Herein we comprehensively review all asymmetric transition-metal-catalyzed methodologies that are believed to proceed via an inner-sphere-type mechanism, with an emphasis on the nature of stereochemistry generation. Our analysis serves to document the considerable and rapid progress within in the field, while also highlighting limitations of current methods.

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Catalytic Enantioselective Transformations Involving C-H Bond Cleavage by Transition-Metal Complexes.

1.

The decarboxylation of acyloxy radicals and the rearrangement of these radicals with 1,5- or 1,6-hydrogen migration are thermodynamically equivalent.




2.

Analysis of the structure of the molecular orbitals of acyloxy radicals shows that the coordination of these radicals with variable-valence metals capable of transferring electron density suppresses the decarboxylation reaction.

Theoretical examination of the competitive decarboxylation and isomerization of acyloxy radicals

The electrochemical oxidation of malonic esters in methanol, ethanol, or acetonitrile in the presence of alkali metal bromides as catalyst-carriers, with the use of 1.8–2 F of electricity per mole of the starting malonic ester leads to esters of propane-1,1,2,2,3,3-hexacarboxylic acid in a yield of up to 90%.

Electrochemical selective trimerization of malonic esters into esters of propane-1,1,2,2,3,3-hexacarboxylic acid in the presence of hydrobromic acid salts

1.

The oxidation of cyanohydrins by the S2O82−-Ag+ system begins with the reaction of the OH group of the cyanohydrin with silver ions, which results in the formation of 1-cyanoalkoxyl radicals. The sulfate ion-radicals practically do not take part in the direct oxidation of cyanohydrins.




2.

The initiation of the oxidation of cyanohydrins by peroxydisulfate in the absence of Ag+ ion proceeds via the cleavage of H atoms from the hydrocarbon groupings of the cyanohydrin by the sulfate ion-radicals. The 4(5)-hydroxy-4(5)-cyanoalkyl radicals, formed as a result of the 1, 4- and 1, 5-migration of the cyano group and subsequent oxidation, are converted to 5- and 6-cyanoalkanones. The oxidative rearrangement of alkanone cyanohydrins to 6-cyanoalkanones was observed for the first time.

Oxidative rearrangement of cyanohydrins with migration of cyano group: Mechanism of initiation by S2O8 2−-Ag+ system

1.

A study was made of the addition reaction, initiated by peroxides, of diethyl malonate, dimethyl succinate and ethyl monochloroacetate to the polyhaloolefins — to hexafluoropropylene, trichloroethylene and tetrachloroethylene.




2.

The reaction proceeds by an anomalous direction: the α-carbon atom of the alcohol portion of the ester molecule takes part either exclusively or predominantly in the formation of the new carbon — carbon bond of the adducts.




3.

The reaction of esters with trichloro- and tetrachloroethylene is accompanied by the elimination of hydrogen chloride and leads to the respective formation of either the 1-(dichlorovinyl) or 1-(trichlorovinyl) derivatives of alkyl esters of carboxylic acids.

G. I. Nikishin

Papers

Theoretical examination of the competitive decarboxylation and isomerization of acyloxy radicals

Electrochemical selective trimerization of malonic esters into esters of propane-1,1,2,2,3,3-hexacarboxylic acid in the presence of hydrobromic acid salts

Oxidative rearrangement of cyanohydrins with migration of cyano group: Mechanism of initiation by S2O8 2−-Ag+ system

Unusual direction of the radical reaction of esters with ethylenic compounds

Manganese (III) acetate-initiated radical reaction of acetone with benzene