Nucleophile substrates

Xenon difluoride [4, 5, 7, 8,10] is a white crystalline material obtained through the combination of fluorine and xenon m the presence of light The reagent is commercially available and possesses a relatively long shelf-life when stored cold (freezer) Xenon difluoride is very effective for small-scale fluormation of alkenes and activated nucleophilic substrates. The reactions are usually conducted between 0 °C and room temperature in chloroform or methylene chloride solutions Hydrogen fluoride catalysis is sometimes helpful Xenon difluoride reacts in a manner that usually involves some complexation between the substrate and reagent followed by the formation of radical and radical cation intermediates... 

The original investigations on the general base catalysis of azo coupling reactions were made with nucleophilic substrates in which the reacting carbon atom was... 

Obviously, the reaction rate of nucleophilic substrates with acylium cations increases as the induced electronic density on C4 increases, thus the N basicity also increases. In onr experiments the reaction rate followed the sequence benzenesulfonamide > p-nitrobenzenesulfonamide > p-... 

In this case the reaction takes place with other C-C multiple bonds rather than with a nucleophile (substrates of type 25). Cydometallation of the Jt-bonds leads either to metallacyde 26 or 27 (Scheme 15.4). Then different pathways are possible, for example /3-hydride elimination and reductive elimination are known. 

Radical cations can dimerize in a radical-radical coupling reaction (Scheme la) to afford dimer dications. An alternative pathway to form the dimer dication is a radical-substrate coupling in an electrophilic addition of the radical cation to the nucleophilic substrate. The dimer dication can lose two protons to form a bis-dehydro dimer or react with two nucleophiles to yield a disubstituted dimer. 

This chapter reports on the reactivity of organic carbonates as alkylating agents, with emphasis on the lightest term of the series, DMC. Under both CF and batch conditions, DMC can react with a number of nucleophilic substrates such as phenols, primary amines, sulfones, thiols, and methylene-active derivatives of aryl and aroxy-acetic acids. The mechanistic and synthetic aspects of these processes will be elucidated. 

The immobilization of nucleophilic substrates such as acids, alcohols, thiols and amines is realized by the Trityl resin (16), which is reasonably acid sensitive [28-30]. 

A -Arylation of a wide range of NH substrates by reaction with boronic acid in the presence of cupric acetate and either triethylamine or pyridine at room temperature. The reaction works even for poorly nucleophilic substrates such as aryla-mide. 

Dimesityldioxirane, a crystalline derivative, has been isolated by Sander and colleagues and subjected to X-ray analysis. The microwave and X-ray data both suggest that dioxiranes have an atypically long 0—0 bond in excess of 1.5 A. Those factors that determine the stability of dioxiranes are not yet completely understood but what is known today will be addressed in this review. A series of achiral, and more recently chiral oxygen atom transfer reagents, have been adapted to very selective applications in the preparation of complex epoxides and related products of oxidation. A detailed history and survey of the rather remarkable evolution of dioxirane chemistry and their numerous synthetic applications is presented in Chapter 14 of this volume by Adam and Cong-Gui Zhao. Our objective in this part of the review is to first provide a detailed theoretical description of the electronic nature of dioxiranes and then to describe the nuances of the mechanism of oxygen atom transfer to a variety of nucleophilic substrates. 

Bis(trimethylsilyl)monoperoxysulfate 6 is also an excellent agent for oxygen transfer to nucleophilic substrates such as alkenes and heteroatoms. Compound 6 could oxidize alkenes such as 1-methylcyclohexene and fraw5-/3-methylstyrene, producing 2-methyl-cyclohexanone and benzyl methyl ketone, respectively, in high yield, most likely via the... 

In the earlier volume of this book, the chapter dedicated to transition metal peroxides, written by Mimoun , gave a detailed description of the features of the identified peroxo species and a survey of their reactivity toward hydrocarbons. Here we begin from the point where Mimoun ended, thus we shall analyze the achievements made in the field in the last 20 years. In the first part of our chapter we shall review the newest species identified and characterized as an example we shall discuss in detail an important breakthrough, made more than ten years ago by Herrmann and coworkers who identified mono- and di-peroxo derivatives of methyl-trioxorhenium. With this catalyst, as we shall see in detail later on in the chapter, several remarkable oxidative processes have been developed. Attention will be paid to peroxy and hydroperoxide derivatives, very nnconunon species in 1982. Interesting aspects of the speciation of peroxo and peroxy complexes in solntion, made with the aid of spectroscopic and spectrometric techniqnes, will be also considered. The mechanistic aspects of the metal catalyzed oxidations with peroxides will be only shortly reviewed, with particular attention to some achievements obtained mainly with theoretical calculations. Indeed, for quite a long time there was an active debate in the literature regarding the possible mechanisms operating in particular with nucleophilic substrates. This central theme has been already very well described and discussed, so interested readers are referred to published reviews and book chapters . 

The second correlation shows that peroxo complexes with k ax values below 400 nm, stretching freqnencies below 900 cm and O-NMR chemical shifts for peroxo moiety below 600 ppm are more efficient oxidants of nucleophilic substrates. 

The most active d metal peroxo complexes toward nucleophilic substrates, like amines, phosphines, thioethers, double bonds etc., are molybdenum, tungsten and rhenium derivatives vanadium and titanium catalysis is also important, in particular when... 

Achiral LSRs are routinely used for resolution enhancement of resonance absorptions and for clarifying the spectra of nucleophilic substrates. 

The reaction of a prostereogenic, nucleophilic substrate (carbanion) with a reagent R1—X, containing an achiral electrophilic part R1 and a chiral nucleofugal leaving group X (PAC/ NEN-reaction) leads within an SN2 reaction to the stereoselective formation of C -C bonds 2 ... 

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