Nucleophile catalyst

Carboxylate anions can also serve as nucleophilic catalysts. In this case, an anhydride is the reactive intermediate ... 

The nucleophilic catalysis mechanism only operates when the alkoxy group being hydrolyzed is not much more basic than the nucleophilic catalyst. This relationship can be imderstood by considering the tetrahedral intermediate generated by attack of the potential catalyst on the ester ... 

Acylation of alcohols is often performed in the presence of an organic base such as pyridine. The base serves two purposes. It neutralizes the protons generated in the reaction and prevents the development of high acid concentrations. Pyridine also becomes directly involved in the reaction as a nucleophilic catalyst (see Section 8.5). 

Line No. Triazine substituents Nucleophile + catalyst Solvent Rate constant (temp. °0) 106 liter mole i sec i Kin param Ex etic eters > JSt Ref. 

Sulfonic esters are most frequently prepared by treatment of the corresponding halides with alcohols in the presence of a base. The method is much used for the conversion of alcohols to tosylates, brosylates, and similar sulfonic esters. Both R and R may be alkyl or aryl. The base is often pyridine, which functions as a nucleophilic catalyst, as in the similar alcoholysis of carboxylic acyl halides (10-21). Primary alcohols react the most rapidly, and it is often possible to sulfonate selectively a primary OH group in a molecule that also contains secondary or tertiary OH groups. The reaction with sulfonamides has been much less frequently used and is limited to N,N-disubstituted sulfonamides that is, R" may not be hydrogen. However, within these limits it is a useful reaction. The nucleophile in this case is actually R 0 . However, R" may be hydrogen (as well as alkyl) if the nucleophile is a phenol, so that the product is RS020Ar. Acidic catalysts are used in this case. Sulfonic acids have been converted directly to sulfonates by treatment with triethyl or trimethyl orthoformate HC(OR)3, without catalyst or solvent and with a trialkyl phosphite P(OR)3. ... 

Reaction of N,N-dimethylaniline with 1-cyanobenziodoxol 1783 to afford N-methyl-N-cyanomethylaniline 1784 in 97% yield has been discussed in Section 12.1 [31]. Analogously, oxidation of dimethylaniline with iodosobenzene and trimethylsilyl azide 19 at 0°C in CDCI3 gives the azido compound 2040 in 95% yield, iodobenzene, and HMDSO 7 [194, 195] (Scheme 12.56). Likewise, the nucleophilic catalyst 4-dimethylaminopyridine (DMAP) is oxidized, in 95% yield, to the azide 2041, which is too sensitive toward hydrolysis to 4-N-methylaminopyri-dine to enable isolation [194, 195]. Amides such as 2042, in combination with tri-... 

Complexes like 64 and 65 can act by two general ways either as a Br0nsted-base or as a nucleophilic catalyst, depending on the type of reaction and substrate. However, the exact mechanistic pathway is in a few cases speculative to some extent as the distinction between the two mechanistic routes is sometimes rather difficult. 

Ruble JG, Fu GC (1996) Chiral tc-complexes of heterocycles with transition metals a versatile new family of nucleophilic catalysts. J Org Chem 61 7230-7231... 

Nguyen HV, Butler DCD, Richards CJ (2006) A metallocene-pyrrolidinopyridine nucleophilic catalyst for asymmetric synthesis. Org Lett 8 769-772... 

The controlled polymerization of (meth)acrylates was achieved by anionic polymerization. However, special bulky initiators and very low temperatures (- 78 °C) must be employed in order to avoid side reactions. An alternative procedure for achieving the same results by conducting the polymerization at room temperature was proposed by Webster and Sogah [84], The technique, called group transfer polymerization, involves a catalyzed silicon-mediated sequential Michael addition of a, /f-unsaluralcd esters using silyl ketene acetals as initiators. Nucleophilic (anionic) or Lewis acid catalysts are necessary for the polymerization. Nucleophilic catalysts activate the initiator and are usually employed for the polymerization of methacrylates, whereas Lewis acids activate the monomer and are more suitable for the polymerization of acrylates [85,86]. 

In the next step of the sequence, the authors sought to introduce a hydroxy-methylene substituent at the unsubstituted 7-position of the enone. This bond construction can be carried out by conducting a Baylis-Hillman reaction with formaldehyde. In this instance, the authors used a modification of the Baylis-Hillman reaction which involves the use of a Lewis acid to activate the enone [26]. Under these conditions, the enone 42 is treated with excess paraformaldehyde in the presence of triethylphosphine (1 equiv), lanthanum triflate (5 mol%), and triethanolamine (50 mol%). It is proposed that the lanthanum triflate forms a complex with the triethanolamine. This complex is able to activate the enone toward 1,4-addition of the nucleophilic catalysts (here, triethylphosphine). In the absence of triethanolamine, the Lewis acid catalyst undergoes nonproductive complexation with the nucleophilic catalyst, leading to diminution of catalysis. Under these conditions, the hydroxymethylene derivative 37 was formed in 70 % yield. In the next step of the sequence, the authors sought to conduct a stereoselective epoxidation of the allylic... 

General-base catalysis can, as the name suggests, be accomplished by any adequately strong base, whereas very special demands are placed upon compounds acting as nucleophilic catalysts. The efficiency of these catalysts depends on three factors basicity, nucleophilicity, and leaving-group ability [166], Each of these characteristics is in turn the combined result of several attributes. 

Even more interesting is the observed regioselectivity of 37 its reaction with 2, 3 -cCMP and 2, 3 -cUMP resulted in formation of more than 90% of 2 -phosphate (3 -OH) isomer. The postulated mechanisms for 37 consists of a double Lewis-acid activation, while the metal-bound hydroxide and water act as nucleophilic catalyst and general acid, respectively (see 39). The substrate-ligand interaction probably favors only one of the depicted substrate orientations, which may be responsible for the observed regioselectivity. Complex 38 may operate in a similar way but with single Lewis-acid activation, which would explain the lower bimetallic cooperativity and the lack of regioselectivity. Both proposed mechanisms show similarities to that of the native phospho-monoesterases (37 protein phosphatase 1 and fructose 1,6-diphosphatase, 38 purple acid phosphatase). 

Nucleophilic catalysts, 10 420 Nucleophibc reagents, 10 389 Nucleophibc substitution in benzene, 3 601 in 1,2-dichloroethane, 6 255 in fullerenes, 12 248 of quinones, 21 261—262 during pulp bleaching, 21 35-38 Nucleosomes, 17 611-612, 613 Nucleotide biosynthesis inhibitors,... 

According to the latter approach, reducing sugars 128 were reacted with triethylammonium dimethyl boranophosphate in the presence of bis(2-oxo-3-oxazolidinyl)phosphinic chloride as condensing reagent, 3-nitro- 1,2,4-triazole as nucleophilic catalyst and A,A-diisopropyl-A-ethyl-amine to provide boranophosphate triester derivatives 129 as anomeric... 

The scheme shows that arylamine plays the role of nucleophilic catalyst reaction of direct condensation of monosaccharide with the ureido derivatives. That is why in order to simplify the synthesis of N-glycosylureas, one can go without N-arylglycozid and instead use the catalyst additions of arylamine [13, 14],... 

In a similar vein, antibody NPN43C9 appears to employ a catalytic histidine, HisL91, as a nucleophilic catalyst in the hydrolysis of a p-nitrophenyl phenylacetate ester, as discussed in detail below (Section 5 Appendix entry 2.8) (Gibbs et al., 1992a Chen et al., 1993). 

Other interesting data in these reactions concern the H/D isotopic effect of the nucleophile/catalyst, for example when [2-hydroxypyridine] = [2 — 02H] = 0.08, fcobsH/ obsD = 1-5. Since a very poor H/D effect is usual in SjvAr reactions with neutral nucleophiles (amines) in apolar solvents10, the authors conclude that the unusually high H/D effect should be due to a difference in the Xh/Xd = 1.75 of the molecular complex. Nevertheless, the same effect could be explained on the basis of an autoassociation of... 

Substrate Nucleophile Catalyst (amt) Time (hr) / temp Product (Yield) ... 

Substrate Nucleophile Catalyst (%) Time/temp Product (yield) ... 

The first class of amine-based nucleophilic catalysts to give acceptable levels of selectivity in the KR of aryl alkyl. yec-alcohols was a series of planar chiral pyrrole derivatives 13 and 14, initially disclosed by Fu in 1996 [25, 26]. Fu and co-workers had set out to develop a class of robust and tuneable catalysts that could be used for the acylative KR of various classes of. yec-alcohols. Planar-chiral azaferrocenes 13 and 14 seemed to meet their criteria. These catalysts feature of a reasonably nucleophilic nitrogen and constitute 18-electron metal complexes which are highly stable [54-58]. Moreover, by modifying the substitution pattern on the heteroaromatic ring, the steric demand and hence potentially the selectivity of these catalysts could be modulated. 

Group-transfer polymerizations make use of a silicon-mediated Michael addition reaction. They allow the synthesis of isolatable, well-characterized living polymers whose reactive end groups can be converted into other functional groups. It allows the polymerization of alpha, beta-unsaturated esters, ketones, amides, or nitriles through the use of silyl ketenes in the presence of suitable nucleophilic catalysts such as soluble Lewis acids, fluorides, cyanides, azides, and bifluorides, HF. ... 

Oxime hgations can be significantly accelerated by using aniline as a nucleophilic catalyst . Rate enhancements are achieved by changing the electrophile from a weakly populated protonated carbonyl (Scheme 2a) to a more highly populated protonated aniline Schiff base (Scheme 2b). The transimination of the protonated aniline Schiff base to the oxime proceeds rapidly under aqueous acidic conditions. 

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