Reagents electrophilic

Most tropolones give sparingly soluble, yellow or orange sodium salts, green cupric chelates, and colored ferric complexes. Although easily acetyl-ated or methylated and frequently precipitated by picric acid, tropolones only exceptionally react with carbonyl reagents. Electrophilic substitution reactions occur readily however, sulfonation or nitration is inhibited... 

Figure 6.12 shows that carboxylic acids can also be converted into acid chlorides without releasing HC1. This is possible when carboxylic acids are treated with the chloroenamine A. First the carboxylic acid adds to the C=C double bond of this reagent electrophilically (see Figures 3.51 and 3.53). Then, the addition product B dissociates completely to give the ion pair C. This constitutes the isopropyl analog of the Vilsmeier-Haack intermediate B of the DMF-catalyzed carboxylic chloride synthesis of Figure 6.11. The new Vilsmeier-Haack intermediate reacts exactly like the old one (cf. previous discussion) The chloride ion undertakes an SN reaction at the carboxyl carbon. This produces the desired acid chloride and isobutyric N, IV-dimethylamide.

Reaction Substrate Reagents Electrophile Intermediate Product... 

Additions to nonactivated olefins and dienes are important reactions in organic synthesis [1]. Although cycloadditions may be used for additions to double bonds, the most common way to achieve such reactions is to activate the olefins with an electrophilic reagent. Electrophilic activation of the olefin or diene followed by a nucleophilic attack at one of the sp carbon atoms leads to a 1,2- or 1,4-addition. More recently, transition metals have been employed for the electrophilic activation of the double bond [2]. In particular, palladium(II) salts are known to activate carbon-carbon double bonds toward nucleophilic attack [3] and this is the basis for the Wacker process for industrial oxidation of ethylene to acetaldehyde [41. In this process, the key step is the nucleophilic attack by water on a (jt-ethylene)palladium complex. 

Polar reactions take place between electron-rich reagents (nucleophiles/ Lewis bases) and electron-poor reagents (electrophiles/Lewis acids). These reactions are heterolylic processes and involve species with an even number of electrons. Bonds are made when a nucleophile donates an electron pair to an electrophile bonds are broken when one product leaves with an electron pair. 

Fehr, C. Diastereoface-selective epoxidations dependency on the reagent electrophilicity. Angew. Chem., Int. Ed. Engl. 1998, 37, 2407-2409. 

Exam )le Typical reagent Electrophile Nucleophile Intermediate Regiochemistry Stereochemistry Product... 

Glycolic acid Nickel acetate reagent, electrolytic zinc Strontium carbonate reagent, electrophilic... 

Nitrogen-containing reagents electrophilic at the N atom such as azodicarboxylate esters, tosyl and nosyl azides, and nitrosobenzene have been successfiilly applied to a variety of organocatalyzed enantioselective amination reactions of carbonyl compounds and other related pronucleophiles. Early work in this area has been covered in previous reviews [1 ], and here the most representative examples are presented. 

NbClj NbMe2Cl3 + ZnCl2 2. From an R+ reagent (electrophilic attack on the metal) ... 

Without additional reagents Electrophilic addition to fluorodlefins Polyfluorodialkylmercury compounds... 

Selective Lithiations.—As in previous years the chemistry of organolithiums totally dominates the Group I metals, and the emphasis has again been towards selective lithiations. Once selectively lithiated, a molecule is then usually reacted with an organic electrophile chosen typically from the halogens, silyl groups, CO2, esters, ketones, aldehydes, oxiranes, and alkyl halides. Since the novelty usually arises in the nature of the lithium reagent, electrophiles of the above types will be represented by E to avoid unnecessary repetition. 

Fig. 6 Some coupling reagents electrophiles, nucleophiles, and combinations...

Addition reactions are simply those reactions, where two or more compounds are added without loss of any fragment (molecule, radical or ion). Addition reactions are truly atom economic reactions (100%) as these use all the atoms of reactants and no waste is produced. The field of addition reactions has not been properly explored as far as microwave-assisted reactions are concerned. These reactions can be basically classified in two categories depending on nature of the attacking reagent electrophilic or nucleophilic. 

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