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.

When reaction is initiated with t-butyl peroxide, carboxylic acids add to one double bond of dialkyldially lsilanes with subsequent homolytic intramolecular cyclization of the intermediately formed free radical with formation of a compound containing a silicon atom in a six-membered ring.

Free-radical addition of aliphatic carboxylic acids to dialkyldiallylsilanes

1.

2-Carboxyethyl radicals add to the C=O group of aldehydes, with the formation of alkoxyl adduct-radicals that cleave H atoms from the aldehyde and are converted toγ-lactones.




2.

2-Carbomethoxyethyl radicals add to the C=O group of biacetyl and ethyl pyruvate, and the obtained adduct-radicals decompose to give methyl levulinate.

Addition of 2-carboxyethyl radicals to carbonyl group

1.

The rate constant for the breakdown of the dimethyl ester of peroxydiglutaric acid (I) in benzene and toluene remains essentially unaltered as the pressure is raised to 10, 000 kg/cm2.




2.

Breakdown of (I) can proceed with rupture of the O-O bond (ka) or with the rupture of three bonds and the evolution of two molecules of CO2 (kb).




3.

Increasing the pressure increases proportion of radical reaction products formed through rupture of the O-O bond.




4.

The rate constant kb, diminishes with rising pressure.




5.

Increasing the pressure decreases the probability of radical reaction in the cage as compared with the probability of radical passage out of the cage.

Thermal decomposition of the dimethyl ester of peroxydiglutaric acid at pressures up to 10,000 kg/cm2

1.

The 3-carboxypropyl and 4-carboxybutyl radicals were generated by the respective decarboxylation of glutaric and adipic acids at 60°C in aqueous solution under the influence of Na2S2O8 in the presence of a catalytic amount of AgNO3, and their transformations under the decarboxylation conditions were studied, and also the effect of added copper ions on these transformations.




2.

The system Na2S2O8-AgNO3-CuSO4 causes an efficient oxidative cyclization of the studiedω-carboxyalkyl radicals, in which connection the 3-carboxypropyl radicals are selectively converted toγ-butyrolactone, while the 4-carboxybutyl radicals are converted to δ-valerolactone to the extent of 90%.




3.

Oxidative cyclization also occurs in the absence of copper ions, but its contribution to the sum of the transformations of the 3-carboxypropyl radicals does not exceed 50%, and not over 30% in the case of the 4-carboxybutyl radicals.

Oxidative cyclization of ω-carboxyalkyl radicals

A new phenomenon, viz. the spontaneous formation of stabilized 1,2-dicarboxyethyl radicals in a crystalline matrix during the complete removal of the solvent from a solution of PDSA and SA in water, methanol, or acetone, was discovered.

G. I. Nikishin

Papers

Free-radical addition of aliphatic carboxylic acids to dialkyldiallylsilanes

Addition of 2-carboxyethyl radicals to carbonyl group

Thermal decomposition of the dimethyl ester of peroxydiglutaric acid at pressures up to 10,000 kg/cm2

Oxidative cyclization of ω-carboxyalkyl radicals

Spontaneous formation of stabilized 1,2-dicarboxyethyl free radicals in the solid system succinic acid-peroxydisuccinic acid