Nucleophilic, Electrophilic and Radical Reactions

This chapter deals with both initial developments as well as more recent advances in the area of polymer-supported nucleophilic and electrophilic reagents, and reagents intended for radical-mediated reactions. Reviews by Kirschning [1] and Ley [2] cover this area up to 2001, and we also refer to the Ley group for reports on the application of polymer-supported reagents in total synthesis [3-5]. More details can also be found in reviews by Bradley [6] and Drewry [7]. 

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Arene(tricarbonyl)chromium complexes undergo a number of synthetically important transformations not usually observed for uncomplexed arenes. The chromium tricarbonyl moiety facilitates nucleophilic, electrophilic, and radical reactions at the benzylic position. Upon complexation, one side of the aromatic ring and adjacent functionalities is blocked by the metal carbonyl moiety and highly stereoselective reactions are usually observed even at relatively remote positions. In addition, the protons of the complexed aromatic ring have a substantially higher acidity and are readily removed and further substituted by electrophiles. Finally, the aromatic ring is activated toward addition reactions using a variety of nucleophiles. 

In summary, polymer-bound reagents for nucleophilic, electrophilic and radical reactions can in many instances be seen as more practical alternatives to the corresponding reaction using soluble reagents, facilitating removal of by-products in... 

Frontier MO (FMO) interactions for nucleophilic, electrophilic, and radical reactions In less symmetric... 

To conclude, silylation of AN and their derivatives made it possible to substantially extend the reactivity of AN. The reactions of AN with nucleophilic, electrophilic, and radical reagents at both the a- and 3-carbon atoms are summarized in Chart 3.24. 

Since they are equivalent to homobutadienes, cyclopropanes interacting directly with an olefin unit display a particularly rich chemistry. Pericyclic reactions come into play in this specific area. Similar to other cyclopropane derivatives, the reactivity of vinylcyclopro-panes with nucleophiles, electrophiles and radicals as well as their general chemical behaviour will be governed by substituents at the cyclopropane core and at the double bond. ... 

Although co r) contains information about both co and /(r) but /(r) alone cannot provide any input regarding co(r) without the knowledge of co. The concept of philicity is widely applicable to diverse types of chemical reactions, which, therefore, presupposes ffl(r) to be represented as o (r)—the symbol of philicity. The sign of a varies with the different categories of reactions, i.e. a = +, -, and 0 represents nucleophilic, electrophilic, and radical attacks, respectively. Thus ... 

Electrophilic and radical reactions have less easily predictable outcomes than nucleophilic reactions. 

In this chapter, we will be studying addition reactions to carbon-carbon multiple bonds this is the converse process of the eliminations that we studied in the previous chapter. Addition to carbon-heteroatom multiple bonds is coming up in Chapter 14. Nucleophiles, electrophiles, and radicals can all add across double bonds first, we will concentrate on electrophiles and radicals, as nucleophiles only add readily when the double bond bears a group (such as a carbonyl, nitro, or nitrile Chapter 17) capable of accepting electron density. Reactions with electrophiles or radicals add two moieties, atoms or groups, by a stepwise process the two atoms or groups are not added simultaneously. However, there is another class of reactions where the two new bonds are made simultaneously—these are called concerted reactions. 

In Volume 13 reactions of aromatic compounds, excluding homolytic processes due to attack of atoms and radicals (treated in a later volume), are covered. The first chapter on electrophilic substitution (nitration, sulphonation, halogenation, hydrogen exchange, etc.) constitutes the bulk of the text, and in the other two chapters nucleophilic substitution and rearrangement reactions are considered. 

Perhaps the most remarkable feature of this reaction is that a bond has formed between C-l and C-5, both of which are positively charged. Any attempt to think of this reaction as the combination of a nucleophilic and an electrophilic carbon would not make proper sense, yet the reaction occurs easily. Pericyclic reactions really are a distinctly different class of reactions from ionic and radical reactions. Since this reaction is also 5-endo-trig at both ends, it would appear to be also deeply forbidden by Baldwin s rules— which evidently do not apply with any great force to electrocyclic reactions. 

Other reactions for which a discussion of their structure-reactivity behavior in terms of the PNS has provided valuable insights include nucleophilic addition and substitution reactions on electrophilic alkenes, vinylic compounds, and Fischer carbene complexes reactions involving carbocations and some radical reactions. 

Covalent dendritic connection can result from any standard synthetic transformation capable of forming a covalent bond. These include nucleophilic, electrophilic, ionic, radical, and carbenoid reactions. Elements effecting bond formation include metals, non-metals, and metaloids. 

Finally attention must be drawn to the fact that the orienting effect of the nitro group in nucleophile and radical reactions usually differs from that in electrophilic reactions, and instead of meta orientation, ortho or para orientation takes place. The corresponding observations are referred to in chapters dealing with nucleophile and radical substitutions of nitro compounds (pp. 204, 207 and 212 respectively). 

Organosilicon compounds receive attack of nucleophilic, electrophilic, and homolytic reagents. The latter is related to the formation of radicals and divalent species. Organosilicon reactive intermediates corresponding to free radicals, carbenium ions, carbanions, and carbenes play important roles in these reactions. These are sUyl radicals, silylium... 

This review article deals primarily with addition reactions of nucleophiles, electrophiles, and neutral radicals to photochemically generated radical ions of organic compounds and some organometallic compounds. Photocyclodimerizations of electron-rich alkenes, photo-Diels-Alder reactions between alkenes and alkadienes via dimer or heterodimer radical cations, and photocycloadditions via triplexes are also included. 

Reactivity (General Topics, Reactions with Electrophiles and Oxidants, Reactions with Nucleophiles and Reducing Agents, Reactions toward Free Radicals, Carbenes, etc., Reactions with Cyclic Transition State, Reactivity of Substituents, Heterocycles as Intermediates in Organic Synthesis). 

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