Electrophilic addition reactions reductive

Diels-Alder reaction, 493 El reaction, 391-392 ElcB reaction, 393 E2 reaction, 386 Edman degradation, 1032 electrophilic addition reaction, 147-148. 188-189 electrophilic aromatic substitution, 548-549 enamine formation, 713 enol formation, 843-844 ester hydrolysis, 809-811 ester reduction, 812 FAD reactions. 1134-1135 fat catabolism, 1133-1136 fat hydrolysis, 1130-1132 Fischer esterification reaction, 796 Friedel-Crafts acylation reaction, 557-558... 

Electrophilic Addition Other Addition Reactions Reduction of Unsaturated Steroids Oxidation and Dehydrogenation Miscellaneous Reactions... 

PAHs are very stable at ambient temperature, but undergo chemical reactions at appropriate conditions. These reactions can be grouped into seven main classes electrophilic substitution, nucleophilic and free radical reaction, addition reaction, reduction and reductive alkylation, oxidation reaction, rearrangements of aromatic ring s) tems, and complex formation. 

The mechanism of the alkoxymercuration reaction is similar to that described in Section 7.4 for hvdroxymercuration. The reaction is initiated by electrophilic addition of Iig2+ to the alkene, followed by reaction of the intermediate cation with alcohol and reduction of the C-Hg bond by NaBH4. A variety of alcohols and alkenes can be used in the alkoxymercuration reaction. Primary, secondary, and even tertiary alcohols react well, but ditertiary ethers can t be prepared because of steric hindrance to reaction. 

The synthesis of a-substituted phosphonates 89, via the electrophilic addition of phosphorylated C-radicals 88 (generated by reaction of BujSnH to the readily accessible a-phosphoryl sulfides (or selenides)) and electrophilic addition to electron rich alkenes, has been described [57] (Scheme 26). A large excess of alkene is necessary to minimize the competitive formation of the undesired compound 90 resulting from direct reduction of the initial radical 88. The ratio 89/90 has been measured for each example. The synthesis of the a-mono- or a,a-di-substituted (R or phosphonates 89 shows that the free radical approach... 

An unexpected reaction occurs when 2-alkyl-4(5)-nitroimidazoles (27 R = alkyl) are reduced in protic solvents [92JCS(P1)2779]. Catalytic hydrogenation of 2-methyl-4(5)-nitroimidazole (27 R = Me) in a solution of acetic anhydride and acetic acid gave 4,4 -diacetamido-2,2 -dimethyl-5,5 -diimidazole (32 yield 10%) in addition to the expected 4-acetamido-l-acetyl-2-methylimidazole (28%). Similarly, reduction of the 2-alkyl-4(5)-nitroimidazoles (27 R = Me, Et, iPr) in ethanol solution in the presence of diethyl ethoxymethylenemalonate [EMME (135)] gives predominantly the 5,5 -diimidazole adducts (33). The formation of these products (33) is believed to involve an electrophilic addition of the starting material (27) to the electron-rich aminoimidazoles (25) [92JCS(P1)2779]. Interestingly, replacement of ethanol by dioxane suppressed diimidazole formation. 

E) Sigma-bond metathesis. Dihydrogen is observed to react with transition-metal-alkyl bonds even when the metal lacks lone pairs. In this case the reaction cannot be explained in terms of the oxidative-addition or reductive-elimination motif. Instead, we can view this reaction as a special type of insertion reaction whereby the ctmr bond pair takes the donor role of the metal lone pair and donates into the cthh antibond. When the M—R bonds are highly polarized as M+R, the process could also be described as a concerted electrophilic H2 activation in which R acts as the base accepting H+. 

This special feature arises from the combination of the transition metal behavior such as the coordination of a carbon-carbon multiple bond, oxidative addition, reductive elimination, P-hydride elimination, addition reactions and the behavior of classical c-carbanion towards electrophiles. 

In this chapter, nucleophilic l,n-additions (n = 4, 6, 8,. ..) to acceptor-substituted dienes, enynes and polyenes are presented2. Addition reactions which obviously proceed via non-nucleophilic pathways (e.g. catalytic reductions, electrophilic or radical additions3), as well as 1,2-additions to the acceptor group, are not covered. 

The present volume contains 13 chapters written by experts from 11 countries, and treats topics that were not covered, or that are complementary to topics covered in Volume 1. They include chapters on mass spectra and NMR, two chapters on photochemistry complementing an earlier chapter on synthetic application of the photochemistry of dienes and polyenes. Two chapters deal with intermolecular cyclization and with cycloadditions, and complement a chapter in Volume 1 on intramolecular cyclization, while the chapter on reactions of dienes in water and hydrogen-bonding environments deals partially with cycloaddition in unusual media and complements the earlier chapter on reactions under pressure. The chapters on nucleophiliic and electrophilic additions complements the earlier chapter on radical addition. The chapter on reduction complements the earlier ones on oxidation. Chapters on organometallic complexes, synthetic applications and rearrangement of dienes and polyenes are additional topics discussed. 

A general type of chemical reaction between two compounds, A and B, such that there is a net reduction in bond multiplicity (e.g., addition of a compound across a carbon-carbon double bond such that the product has lost this 77-bond). An example is the hydration of a double bond, such as that observed in the conversion of fumarate to malate by fumarase. Addition reactions can also occur with strained ring structures that, in some respects, resemble double bonds (e.g., cyclopropyl derivatives or certain epoxides). A special case of a hydro-alkenyl addition is the conversion of 2,3-oxidosqualene to dammara-dienol or in the conversion of squalene to lanosterol. Reactions in which new moieties are linked to adjacent atoms (as is the case in the hydration of fumarate) are often referred to as 1,2-addition reactions. If the atoms that contain newly linked moieties are not adjacent (as is often the case with conjugated reactants), then the reaction is often referred to as a l,n-addition reaction in which n is the numbered atom distant from 1 (e.g., 1,4-addition reaction). In general, addition reactions can take place via electrophilic addition, nucleophilic addition, free-radical addition, or via simultaneous or pericycUc addition. 

Electrophilic addition to 9-vinylcarbazole occurs in the Markovnikov sense, thus hydrogen chloride,hydrogen bromide,chlorine, and bromine in carbon tetrachloride, and iodine chloride in pyridine are recorded as adding with initial electrophilic attack at the methylene. Mercuric acetate in methanol gave 9-(2-acetoxymercuri-l-methoxyethyl)carbazole. Although 9-vinylcarbazole gave an iodohydrin, comparable reaction with methanolic sodium hypochlorite led to 9-(2-chlorovinyl)carbazole. Catalytic reduction of the latter produced 9-(2-chloroethyl)carbazole. Tri-phenyltin hydride gave 96. ... 

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