Creation of carbon

Quiclet-Sire B, Zard SZ (2006) The Degenerative Radical Transfer of Xanthates and Related Derivatives An Unusually Powerful Tool for the Creation of Carbon-Carbon Bonds. 264 201-236... 

As mentioned above, for more than 20 years after the first preparation of zirconacyclopen-tadiene, no systematic carbon—carbon bond-forming reactions were investigated. The major reason was the low nucleophilicity of the zirconacyclopentadienes. Indeed, such was the reputation of zirconacyclopentadienes in the 1980s that they were referred to as dead-end compounds . This statement clearly emphasizes the assumption that zirconacyclopentadienes were completely inert with regard to the creation of carbon—carbon bonds. In this context, transmetalation of zirconacyclopentadienes to copper and subsequent carbon—carbon bond formation represents a milestone in zirconacyclopentadiene chemistry. 

The creation of carbon, like that of the other elements, is part of the history of the universe. All but the lightest of the natural elements were created in the cores of stars at extreme temperatures. In this process, called nucleosynthesis, protons are smashed together to form nuclei with more and more protons (heavier and heavier elements). Carbon was formed by collisions of three helium nuclei, each... 

Copper was also effective in the creation of carbon-nitrogen bonds. N-(o-halophenyl)-guanidines gave 2-aminobenzimidazoles in the presence of a copper-1,10-phenantroline catalyst system. While the iodo and bromo derivatives in the presence of the copper catalyst gave the cyclized product in 83% and 96% yields respectively, the analogous palladium catalysed transformation showed similar efficiency in both cases, resulting in 88% and 86% yields.52... 

Spi-zinc carbenoids such as (iodomethyl)zinc iodide or bis(iodomethyl)zinc have also been used for the selective creation of carbon-carbon bonds through a methylene homologation.295... 

In this chapter, the main focus will be on two types of reactions deahng with both the creation of carbon-carbon bonds on amino acids and peptides and carbon-carbon bond fragmentations, all of which proceed via radical intermediates. Much of the earlier work on the use of free radical reactions in the synthesis of a-amino acids and derivatives has been pubhshed in an extensive review in 1997 by Easton [1]. 

An Unusually Powerful Tool for the Creation of Carbon-Carbon Bonds... 

The radical chemistry of xanthates and related derivatives has proved to be extraordinarily powerful for the creation of carbon-carbon bonds. In add-... 

On the other hand, creation of carbon-carbon bonds from ArX by addition to activated olefins could be achieved [22]. 

Carbon electronics started from the investigation of diamond single crystals (sp -type hybridization) because the diamond crystal structure is similar to that of Si and Ge. It was expected that both p- and n-type doping could be achieved in diamond to obtain the basic element of solid-state electronics that is, the p-n junction. However, the conductivity of only the p-type was realized in diamond and it was the main obstacle to the creation of carbon electronics. Nevertheless, there is an alternative route to the creation of hetero-junctions by use of the highly oriented sp -hybridized carbon films doped by different elements. 

The I-V curve is found to have Schottky-type dependence under forward biased conditions. This means that a semiconducting diode can be successfully fabricated using the sp /sp junction in the carbon-based structure. This result opens up a promising route to the creation of carbon electronics on the basis of using junctions consisting of carbon films with various types of electron hybridization with the aid of different dopants. 

Irreversible attachment of side chains is achieved by O- and Ai-alkylation and creation of carbon-carbon bonds. The grafted side chains can be basic (dimethylaminoethyl or morpholinoethyl chains), acidic (carboxylic, sulfonic, etc.) or neutral (glyceryl). 

An exposure sequence obtained at room temperature is presented in Fig. 4.21. For small dosages (1 L in Fig. 4.21a) the surface is relatively smooth with single localized areas being depressed. For higher exposures (20 L in Fig. 4.21b) the appearance has been changed. As will be discussed in more detail below the rough surface points to the creation of carbonate species. 

In the next step the reaction changes only half a rate of hydrogen is removed as can be seen by the change in slope for the H induced feature in Fig. 4.23. Thus, another reaction seems to occur. The additional amount of CO causes the creation of carbon on or near the surface but no oxygen atom is adsorbed. The reaction can therefore be written as... 

The next step is characterized by the creation of carbon and Gd suboxide through direct CO dissociation ... 

Very recently, deprotonation-electrophile trapping of simple meso-epoxides was applied to medium-sized meso-cycloalkene oxides [77]. When cyclooctene oxide 62 is treated with s-BuLi in the presence of a diamine at -90°C, the Hthiated epoxide is stable enough to be trapped with a wide range of electrophiles, allowing the creation of carbon-heteroatom or carbon-carbon bonds [Eq. (33)]. The deprotonation is a symmetry-breaking step, and enantioselective deprotonation was successfully achieved in the presence of (-)-sparteine, leading to a range of enantio enriched functionalised epoxides 115 (in up to 86% ee). 

Applications of NHC in organocatalysis by way of formation of homoenolates for the creation of carbon-carbon bonds have been detailed from a mechanistic and stereochemical point of view. The NHC-organocatalysed hydroacylation of unactivated alkenes has been highlighted. The double nucleophilic character of NHC (nucleophile, which upon addition to an aldehyde generated a new nucleophile) has been... 

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