Electrophilic reactions catalysis

ELECTRON TRANSEER REACTIONS ELECTRON TRANSPORT ELECTROPHILE ELECTROPHILICITY NUCLEOPHILE ELECTROPHILIC CATALYSIS ELECTROPHILICITY NUCLEOPHILICITY ELECTROPHILE ELECTROPHILIC SUBSTITUTION REACTION Electrophoretic mobility,... 

This does not occur in the case of catalyst and reactants here described. With Bronsted-type catalysis, the reaction between the benzoyl cation, Ph-C" =0, and the hydroxy group in phenol is quicker than the electrophilic substitution in the ring. This hypothesis has been also confirmed by running the reaction between anisole and benzoic acid in this case the prevailing products were (4-methoxy)phenylmethanone (the product of para-C-benzoylation) and methylbenzoate (obtained by esterification between anisole and benzoic acid, with the co-production of phenol), with minor amounts of phenylbenzoate, phenol, 2-methylphenol and 4-methylphenol. Therefore, when the 0 atom is not available for the esterification due to the presence of the substituent, the direct C-acylation becomes the more favored reaction. 

The products formed in these reactions are very sensitive to the functionality on the carbenoid. A study of Schechter and coworkers132 using 2-diazo-1,3-indandione (152) nicely illustrates this point. The resulting carbenoid would be expected to be more electrophilic than the one generated from alkyl diazoacetate and consequently ihodium(II) acetate could be used as catalyst. The alkylation products (153) were formed in high yields without any evidence of cycloheptatrienes (Scheme 33). As can be seen in the case for anisole, the reaction was much more selective than the rhodium(II)-catalyzed decomposition of ethyl diazoacetate (Scheme 31), resulting in the exclusive formation of the para product. Application of this alkylation process to the synthesis of a novel p-quinodimethane has been reported.133 Similar alkylation products were formed when dimethyl diazomalonate was decomposed in the presence of aromatic systems, but as these earlier studies134 were carried out either photochemically or by copper catalysis, side reactions also occurred, as can be seen in the reaction with toluene (equation 36). 

The fate of the onium carbanion Q+R incorporated into the organic phase depends on the electrophilic reaction partner. The most studied area in the asymmetric phase-transfer catalysis is that of asymmetric alkylation of active methylene or methine compounds with alkyl halides, in an irreversible manner. The reaction mechanism illustrated above is exemplified by the asymmetric alkylation of glycine Schiff base (Scheme 1.5) [8]. 

Arasabenzene, with chromium, 5, 339 Arcyriacyanin A, via Heck couplings, 11, 320 Arduengo-type carbenes with titanium(IV), 4, 366 with vanadium, 5, 10 (Arene(chromium carbonyls analytical applications, 5, 261 benzyl cation stabilization, 5, 245 biomedical applications, 5, 260 chiral, as asymmetric catalysis ligands, 5, 241 chromatographic separation, 5, 239 cine and tele nucleophilic substitutions, 5, 236 kinetic and mechanistic studies, 5, 257 liquid crystalline behaviour, 5, 262 lithiations and electrophile reactions, 5, 236 as main polymer chain unit, 5, 251 mass spectroscopic studies, 5, 256 miscellaneous compounds, 5, 258 NMR studies, 5, 255 palladium coupling, 5, 239 polymer-bound complexes, 5, 250 spectroscopic studies, 5, 256 X-ray data analysis, 5, 257... 

Instead of adding two hydrogen atoms to an alkynyl silane we could add H and SiMe3 to a simple alkyne by hydrosilylation (addition of hydrogen and silicon). This is a cis addition process catalysed by transition metals and leads to a tram (E-) vinyl silane. One of the best catalysts is chloroplatinic acid (H2PtCl6) as in this formation of the E-vinyl silane from phenylacetylene. In this case photochemical isomerization to the Z-isomer makes both available. Other than the need for catalysis, this reaction should remind you of the hydroboration reactions earlier in the chapter. The silicon atom is the electrophilic end of the Si-H bond and is transferred to the less substituted end of the alkyne. 

S.C. PanandB. List s paper spans the whole field of current organocat-alysts discussing Lewis and Brpnsted basic and acidic catalysts. Starting from the development of proline-mediated enamine catalysis— the Hajos-Parrish-Eder-Sauer-Wiechert reaction is an intramolecular transformation involving enamine catalysis—into an intermolecular process with various electrophilic reaction partners as a means to access cY-functionalized aldehydes, they discuss a straightforward classification of organocatalysts and expands on Brpnsted acid-mediated transformations, and describe the development of asymmetric counteranion-directed catalysis (ACDC). 

MF5 and MCI5 are strongly electrophilic see Electrophile and Electrophilic Reaction) and catalyze Friedel-Crafts reactions. The HF/TaFs system is a superacid catalyst and has been used in the selective acid-catalyzed isomerization and hydrogenolysis of cycloalkanes. Oligomerization and polymerization of alkynes with Nb and Ta halides as catalysts have been reported see Oligomerization Polymerization by Homogeneous Catalysis) ... 

Vinyl silanes resemble alkenes in reactivity they combine with reactive electrophiles such as bromine without catalysis but need Lewis acid catalysis for reaction with carbon electrophiles. Reaction usually occurs 189 at the silyl end of the alkene so that the intermediate 190 enjoys the P-silyl stabilisation of the carbocation. The silyl group is removed by a nucleophile, usually a halide ion.45... 

Catalysis of Electrophilic Reactions by Proton Loss from a Coordinated Ligand... 

Under Lewis add catalysis, the reaction of allylsilanes takes place easily with a-enones but not with a,P-unsaturated esters [162]. Because disappointing results were obtained in reactions of allylmetals with a,P-unsaturated carbonyl compounds, reactions of allylsilanes with electrophiles bearing chiral auxiliaries have been examined. Schultz and Lee [1435] performed the T1CI4 catalyzed addition of trimethylallylsilane to compound 7.67 at -78°C. After treatment with methylhy-droxylamine in acidic media, the 1,4-adduct 7.80 was obtained with high ee (Figure 7.56). Under similar conditions, N-enoyloxazolidinone 7.68 (R = Ph) or sultam... 

Zaraisky. A.P. Kachurin. O.I. Velichko, L.I. Shur. V.B. Tikhonova. LA. Furin. G.G. Phase transfer catalysis in reactions of electrophilic substitution. VIII. Phase transfer catalytic nitration of arenes with sodium nitrite in an acidic medium. Zh. Org. Khim. 1999, 35. 1063-1067. 

J.A. Boon, S.W. Lander, J.A. Levisky, J.L. Pflug, L.M. Skrynecki-Cooke and J.S. Wilkes Catalysis and reactivity of electrophilic reactions in room-temperature chloroaluminate molten-salts, J. Electrochem. Soc., 134,510,(1987). 

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