Acyl nucleophile attack

The concept that by carrying out a surface analysis on a model specimen one can obtain direct access to the interphase chemistry is a potentially very exciting and rewarding idea. The interaction of PMMA with various metals (as exemplified hyO Fig. 10.14 above) has been studied in some detail using high resolution XPS (Leadley and Watts 1997). In this work the manner in which PMMA formed specific interactions with oxidized metal surfaces was studied by the nature of the fine structure in the XPS spectrum. In this manner, it was possible to show that the polymer formed hydrogen bonds with oxidised silicon (an acidic substrate), a bidentate structure with oxidised aluminum (an amphoteric substrate) and would undergo acyl nucleophilic attack with oxidised nickel (a basic substrate). 

Acyl derivatives of azoles containing two different environments of nitrogen atoms can rearrange. For example, 1-acyl-1,2,3-triazoles are readily isomerized to the 2H-isomers in the presence of triethylamine or other bases the reaction is intermolecular and probably involves nucleophilic attack by N-2 of one triazole on the carbonyl group attached to another (74AHC(16)33). 

Imidazolium halides pyrolysis, 5, 449 Imidazolium ions acylation, 5, 402 H NMR, 5, 352 hydrogen exchange, 5, 417 nucleophilic attack, 5, 375 reactivity, 5, 375 ring opening, S, 375 Imidazolium oxides in pyrrole synthesis, 4, 344 Imidazolium perchlorate, 1,3-diphenyl-acylation, 5, 402 Imidazolium salts 1-acetyl-... 

Isoxazole, 3-acetyl-4-chloro-5-methyl-oxidation, 6, 27, 53 Isoxazole, 3-acetyl-4,5-dimethyl-oxidation, 6, 27, 53 Isoxazole, 5-acetyl-3-methoxy-reactions, 6, 53 Isoxazole, 3-acyl-furazans from, 6, 417 nucleophilic attack, S, 93 reactions with bases, 6, 30... 

Ketenes undergo rapid addition by nucleophilic attack at the sp-carbon atom. The reaction of tertiary amines and acyl halides, in the absence of nucleophiles, is a general preparation for ketenes. ... 

On the basis of these findings, the reaction of acyl imines with methanesulfony 1 chloride-triethylamine is not expected to proceed via a sulfene intermediate as previously proposed [99]. Again, a carbanion intermediate accounts nicely for the experimental facts. The electrophihcity of the hetero-l,3-diene is exdemely high, therefore the carbanion, formed on reaction of triethylamme with methanesulfonyl chloride, should undergo nucleophilic attack at C-4 of the hetero-1,3-diene faster than sulfene formabon by chloride elimination. 

The 5/) -hybridized carbon of an acyl chloride is less sterically hindered than the sp -hybridized carbon of an alkyl chloride, making an acyl chloride more open toward nucleophilic attack. Also, unlike the Sn2 transition state or a carbocation intennediate in an SnI reaction, the tetrahedral intennediate in nucleophilic acyl substitution has a stable anangement of bonds and can be fonned via a lower energy transition state. 

Nucleophilic acyl substitution reaction (Section 21.2) A reaction in which a nucleophile attacks a carbonyl compound and substitutes for a leaving group bonded to the carbonyl carbon. 

The reported preparations of enantiomerically pure chiral iron-acyl complexes have relied upon resolutions of diastereomers. One route1415 (see also Houben-Weyl, Vol. 13/9 a, p 421) employs a resolution of the diastereomeric acylmenlhyloxy complexes (Fe/ )-3 and (FeS )-3 prepared via nucleophilic attack of the chiral menlhyloxide ion of 2 at a carbon monoxide of the iron cation of 1. Subsequent nucleophilic displacement of menthyloxide occurs with inversion at iron to generate the enantiomerically pure iron-acyl complexes (i>)-4 and (f )-4. 

A detailed mechanism of Goldschmidt s process has not been given two reaction paths are possible either proton transfer to the acid with the formation of RC(OH) (in which case the slow step would be an Aac2 Ingold mechanism) or nucleophilic attack of the carbonyl group of the acid on the protonated alcohol. The second mechanism would require an alkyl scission (A l). In more recent studies2501, it has been shown that scission in most cases is of the acyl type and particularly in the examples studied by Goldschmidt. 

Brown and Jensen395 suggested that the rate equation (194) for the reaction of benzene with excess benzoyl chloride could be interpreted according to the mechanisms given by the reactions (201) and (202), (203) and (204) and (205) and (206) which refer to nucleophilic attack of the aromatic upon the polarised acyl halide-catalyst complex, upon the free acylium ion, and upon an ion pair derived from the acyl halide-catalyst complex, viz. 

Abstract The photoinduced reactions of metal carbene complexes, particularly Group 6 Fischer carbenes, are comprehensively presented in this chapter with a complete listing of published examples. A majority of these processes involve CO insertion to produce species that have ketene-like reactivity. Cyclo addition reactions presented include reaction with imines to form /1-lactams, with alkenes to form cyclobutanones, with aldehydes to form /1-lactones, and with azoarenes to form diazetidinones. Photoinduced benzannulation processes are included. Reactions involving nucleophilic attack to form esters, amino acids, peptides, allenes, acylated arenes, and aza-Cope rearrangement products are detailed. A number of photoinduced reactions of carbenes do not involve CO insertion. These include reactions with sulfur ylides and sulfilimines, cyclopropanation, 1,3-dipolar cycloadditions, and acyl migrations. 

Sulfur-stabilized ylides underwent photodriven reaction with chromium alkoxy-carbenes to produce 2-acyl vinyl ethers as E/Z mixtures with the E isomer predominating (Table 22) [ 121-123]. The reaction is thought to proceed by nucleophilic attack of the ylide carbon at the chromium carbene carbon followed by elimination of (CO)5CrSMe2. The same reaction occurred thermally, but at a reduced rate. Sulfilimines underwent a similar addition/elimination process to produce imidates or their hydrolysis products (Table 23) [ 124,125]. Again the reaction also proceeded thermally but much more slowly. Less basic sulfilimines having acyl or sulfonyl groups on nitrogen failed to react. 

As shown, an asymmetric carboxylic-sulfonic acid anhydride is formed, but the cellulose attack occurs on the C = O group, since a nucleophilic attack on sulfur is slow, and the tosylate moiety is a much better leaving group than the carboxylate group [193]. Similar to other acylation reactions, there is a large preference for tosylation at the 5 position, and cellulose tosylates... 

D. Coenzyme A.—Succinyl phosphate (42) reacts rapidly and non-enzymatically with CoA in the pH range 3—8 to yield succinyl CoA (43). This reaction is dependent on the presence of a suitably situated free carboxy-group as such nucleophilic attack at carbon is not known with other acyl phosphates. Moreover, maleyl phosphate reacts rapidly with CoA while fumaryl phosphate fails to react under the same conditions. Hence the formation of a cyclic intermediate (44) from succinyl phosphate is... 

These A -acyl phosphazenes also decompose further on heating to PhaMePO and RCN. The elimination of methyl iodide probably occurs by a course closely related to the elimination of alkyl halides in the Arbusov reaction, where the alkoxy-group undergoes nucleophilic attack by halide ion. 

The pKj, value (2.43) of the hydration constant of the cyanidin was found to be lower than the pKj, values of glycosylated and acylated cyanidins, meaning lower resistance of the anthocyanidin to hydration. The stability of nonacylated 3,5-diglucosides was lower compared to the 3-glucoside because the 5 position markedly lowered the hydration constant due to decreased electron density of the pyrilium ring that favors nucleophilic attack by water, enhancing hemiacetal formation. ... 

The reaction of Ccf -ATPase with dicyclohexylcarbodiimide Carbodiimides readily react in aqueous solutions with protein amino, carboxyl and sulfhydryl groups slower reactions with tyrosine and serine have also been reported [369,370]. The primary reaction product of carboxyl groups with dicyclohexylcarbodiimide is dicyclohexyl-O-acyl isourea [370]. Dicyclohexyl-O-acyl isourea is susceptible to nucleophilic attack either by water or by endogenous or exogenous nucleophiles, yielding a complex series of reaction products [369-371]. 

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