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.

The oxidation of primary aliphatic alcohols by the Na2S2O8-alkali metal chloride system in water in the presence of sulfuric acid gives 1,1-dialkoxy-2-chloroalkanes.

Oxidation of aliphatic alcohols by a system containing Na2S2O8 and a metal chloride

1.

The LTA-Cu(OAc)2-mediated oxidation of tertiary cyclic alcohols produces cycloalkoxy radicals

(R=alkyl; n=4–5), which undergo Β-fragmentation along two pathways: a) with ring opening to generate oxoalkyl radicals RCO(CH2)n-1CH2, which are oxidized quantitatively to Ω-unsaturated ketones, and b) with elimination of alkyl radicals (R.) and the formation of cycloalkanones. This reaction forms the basis for the synthesis of Ω-unsaturated ketones.




2.

The relative rates for the two pathways of Β-decomposition depend upon the structure of the alkyl substituent. The frequency of Β-fragmentation via ring cleavage increases as the stability of the departing radical (R.) decreases:

$$\dot CH_3< RCH_2 \dot CH_2< CH_3 \dot CH_2< (CH_3 )_2 \dot CH< (CH_3 )_3 \dot C< C_6 H_5 CH_2$$

.




3.

The oxidation of 1-alkylcyclohexanols in which the alkyl groups exceed four carbon atoms results in the formation of alkoxy radicals which undergo oxidative cyclization and are converted into 2-alkyl-5-pentamethylenetetrahydrofurans.

Pb(OAc) 4 -Cu(OAc) 2 -mediated oxidation of 1-alkylcyclohexanols; β-decomposition of 1-alkylcycloalkoxy radicals

A synthetic method of preparing 5-bromopentanoic acid was develope by oxidation of cyclopentanone with aqueous solutions of H2O2. Subsequent decomposition of the resulting hydroperoxide of cyclopentanone was accomplished with a catalytic quantity of copper salt in the presence of alkali bromides.

Synthesis of 5-bromopentanoic acid through catalytic decomposition of the hydroperoxides of cyclopentanone

1.

Oxidation of dialkyl sulfones with systems containing sodium peroxydisulfate results in remote functionalization, the site of which is dependent on the length of the alkyl chain, in agreement with polar control of this reaction by the electron-acceptor sulfonyl group.




2.

Butyl alkyl sulfones are selectively oxidized by Na2S2O8 to 3-oxobutyl alkyl sulfones, and oxidative chlorination in the system Na2S2O8-CuCl2 gives 3- and 4-chlorobutyl alkyl sulfones, the γ-chlorination products predominating.

Polar control in the remote oxidative functionalization of sulfones

Synthesis of 1,1′-Bishydroperoxydi(cycloalkyl) Peroxides by Homocoupling of 11—15-Membered gem-Bis(hydroperoxy)cycloalkanes in the Presence of Boron Trifluoride.

G. I. Nikishin

Papers

Oxidation of aliphatic alcohols by a system containing Na2S2O8 and a metal chloride

Pb(OAc) 4 -Cu(OAc) 2 -mediated oxidation of 1-alkylcyclohexanols; β-decomposition of 1-alkylcycloalkoxy radicals

Synthesis of 5-bromopentanoic acid through catalytic decomposition of the hydroperoxides of cyclopentanone

Polar control in the remote oxidative functionalization of sulfones

Synthesis of 1,1′-Bishydroperoxydi(cycloalkyl) Peroxides by Homocoupling of 11—15-Membered gem-Bis(hydroperoxy)cycloalkanes in the Presence of Boron Trifluoride.