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 selective electrochemical bromoalkoxylation of olefins has been achieved using a membrane-free (diaphragmless) cell to give bromoethers in 60–95% yields, under conditions of cathodic conversion of dibromides formed via competing side reactions back to the olefin precursors.




2.

Bromide ion has been found to catalyze the electrochemical addition of methanol to allylbenzene, resulting in the formation of ethers in 75% yield.

Selective electrochemical bromoalkoxylation of aryl olefins

The addition of esters to unsaturated epoxy compounds, initiated by di-t-butyl peroxide, forms esters containing an epoxy group.

Free radical addition of carboxylic esters to unsaturated epoxy compounds

The kinetics of the reaction of the butyraldehyde with 1-heptene in acetic acid by the action of Mn(III) acetate (in an inert atmosphere) supports the previously proposed mechanism for the catalytic alkylation of aldehydes by olefins. In accord with this mechanism, the selectivity in the formation of α-alkyl-substituted aldehydes is attributed to the reaction proceeding in the coordination sphere of the metal.

Kinetics of the alkylation of butyraldehyde by 1-heptene in acetic acid by the action of Mn(III) acetate

When reaction is initiated with t-butyl peroxide, 2-pyrrolidinone reacts with α-olefins with formation of mixtures of 3- and 5-alkyl-2-pyrrolidinones with the latter isomer in the predominating amount.

Free-radical addition of 2-pyrrolidinone to α-olefins

Catalytic cyclization of γ,σ-unsaturated aldehydes (intramolecular hydroacylation) in the presence of (PPh3)2Co(Ph2PCH2CH2PPh2) gives four-membered and five-membered cycloalkanones. Depending on aldehyde structure the selectivity is 90–97% at 10–100% aldehyde conversion.

G. I. Nikishin

Papers

Selective electrochemical bromoalkoxylation of aryl olefins

Free radical addition of carboxylic esters to unsaturated epoxy compounds

Kinetics of the alkylation of butyraldehyde by 1-heptene in acetic acid by the action of Mn(III) acetate

Free-radical addition of 2-pyrrolidinone to α-olefins

Cyclization of unsaturated aldehydes catalyzed by (PPh3)2Co(Ph2PCH2CH2PPh2)