Nucleophilicity Mayr scale

Dinitrobenzofuroxan (DNBF) is known as a superelectrophile due to its high reactivity both as an electrophile and in its pericyclic addition reactions. NMR studies show that reaction with 2-aminothiazole and its 4-methyl derivative yield anionic carbon-bonded adducts such as (11) by reaction at the 5-position, whereas the 4,5-dimethyl derivative reacts via the exocyclic amino group. Kinetic studies of the first two compounds, both in acetonitrile and in 70 30 (v/v) water-DMSO, have been used to assess their carbon nucleophilicities and place them on the Mayr nucleophilicity scale.55 In a related study, the nucleophilic reactivity, in acetonitrile, of a series of indoles with both DNBF and with benzhydryl cations have been compared and used to determine nucleophilicity parameters for the indoles.56... 

MAOS (microwave-assisted organic synthesis) 593 marine alkaloids 1058 Mayr nucleophilicity scale 396 Mayr reactivity scale 730, 731 M B H (M orita-Baylis-Hillman) adducts 1204... 

Six-membered cyclic nitronates can be involved in C,C-coupling reactions with other C-centered nucleophiles having high nucleophilicity on Mayr s scale (481). This was demonstrated by the reactions of nitronate (356a) (Scheme 3.210). 

Recent works of Mayr and co-workers4-14 have illustrated this trend. In fact, these authors have established, in contrast to the accepted opinion about the relative character of the experimental electrophilicity/nucleophilicity scales for many reactions in organic and organometallic chemistry, that it would be possible to define nucleophilicity and electrophilicity parameters that are independent of the reaction partners. Mayr et al. proposed that the rates of reactions of carbocations with uncharged nucleophiles obey the linear free energy relationship given by 4-14... 

Using Mayr s nucleophilic scale (see Sect. 1.1) as a guide, Westermaier and Mayr concluded that indole should compete with solvent for allylic cations in aqueous acetonitrile or acetone. This was shown to be the case experimentally [87]. Several allylic chlorides and bromides react with indole or 1-methylindole to provide allylation products. Unsymmetrical cations react at the less substituted position. Interestingly, significant amounts of 2-substituted indoles are generated under these conditions (usually about 10 1 for C-3 C-2). 

Following from the examples of allyltrichlorosilanes 21.5, Denmark introduced the related eno)g4 richlorosilanes 21.97 (Scheme 21.13) to cany out Mukaiyama-lype nucleophilic additions to carbonyl compounds. " According to Mayr s nucleophilicity scale, silyl enol ethers derived from aldehydes and ketones and, in particular, silyl ketene acetals are even more powerful nucleophilic reagents than the respective allyl silanes. Indeed, the aldol-type addition of trichlorosilyl enol ethers 21.97a-d to aldehydes 21.4 proceeds readily at room temperature without a catalyst exhibiting simple first-order kinetics in each component (Scheme 21.13), which contrasts with the lack of reactivity of allyl silanes in the absence of a catalyst. 

It is generally believed that it was Ingold [1] in the early 1930s who proposed the first global electrophilicity scale to describe electron-deficient (electrophile) and electron-rich (nucleophile) species based on the valence electron theory of Lewis. Much has been accomplished since then. One of the widely used electrophilicity scales derived from experimental data was proposed by Mayr et al. [5-12] ... 

H. Mayr, M. Patz, Scales of Nucleophilicity and Electrophilicity A System for Ordering Polar Organic and Organometallic Reactions, Angew. Chem. Int. Ed. Engl. 1994, 33, 938-958. 

Mayr and Patz have recently evaluated 56 reaction series, mostly for reactions as described in this article, and derived Eq. (23), in which carbo-cations are characterized by the electrophilicity parameter E, whereas nucleophiles are characterized by the nucleophilicity parameter N and the slope parameter s [182]. The latter quantity, s, which basically describes the slopes of plots as shown in Figs. 10 and 11, ranges from 0.8 to 1.2 for 91 % of the 7r-nucIeophiles investigated. The mathematical form of Eq. (23) implies that the exact value of s will usually only be of importance when rate constants, which strongly deviate from 1 (e.g., (log > 5), are considered. Some of the characterized nucleophiles and electrophiles are listed in Scheme 53, where the two scales are arranged in such a way that electrophiles and nucleophiles which are located at the same level are predicted to combine with rate constants of lg k = -5 s. With s 1 one expects slow combinations for electrophile-nucleophile pairs at the same level, whereas reactions of nucleophiles with electrophiles located below them are expected to be very slow or not to occur at all at 20° C. 

A considerable improvement in the construction of reference scales for the quantitative characterization of nucleophiles and electrophiles in solution has been made by Mayr et al. [598] by means of Eq. (5-109a),... 

Mayr H, Patz M (1994) Scales of nucleophilicity and electrophilicity a system for ordering polar organic and organometallic reactions. Angew Chem Int Ed 33 938-957... 

Mayr H, Bug T, Gotta MF, Hering N, Irrgang B, Janker B, Kempf B, Loos R, Ofial AR, Remennikov G, Schimmel H (2001) Reference scales for the characterization of cationic electrophiles and neutral nucleophiles. J Am Chem Soc 123 9500-9512... 

Living cationic sequential block copolymerization is one of the simplest and most convenient methods to provide well-defined block copolymers. The successful synthesis of block copolymers via sequential monomer addition relies on the rational selection of polymerization conditions, such as Lewis acid, solvent, additives, and temperature, and on the selection of the appropriate order of monomer addition. For a successful living cationic sequential block copolymerization, the rate of crossover to a second monomer ( ) must be faster than or at least equal to that of the homopolymerization of a second monomer (i p). In other words, efficient crossover could be achieved when the two monomers have similar reactivities or when crossover occurs from the more reactive to the less reactive monomer. When crossover is from the less reactive monomer to the more reactive one a mixture of block copolymer and homopolymer is invariably formed because of the unfavorable Rcr/Rp ratio. The nucleophilicity parameter (N) reported by Mayr s group might be used as the relative scale of monomer reactivity [171]. 

Mayr, H., Patz, M. (1994). Nucleophilic and electrophihc scales as the principles for classification of polar organic and organometalhc reactions. Angewandte Chemie International Edition, 33,938—955. 

Mayr and co-workers extended their investigations of nucleophilicity and basicity scales to the development of a scale of nucleofugality as well. They found that kinetic data could be correlated with a relationship in the form of equation 8.52. ... 

Mayr has extended his electrophilicity scale to benzaldehyde-derived iminium ions through measurement of rate constants for their reactions with C-nucleophiles such as enamines, silylated ketene acetals and enol ethers." With an E value of -9.27 for Ph-CH=NMe2" (in a range from -8.34 to -10.69 forpara-C j, andpura-OMe, respectively), these iminium ions are 10 orders more reactive than the parent aldehydes. However, the values are restricted to C-nucleophiles the iminium ions react 10 -10 times faster with water and amines than these E values would predict. Such reactions benefit from the anomeric stabilization of 0,Af-acetals and Af,Af-aminals. 

An intrinsic reactivity index (IRI) has been developed, with a view to capturing electro-and nucleophilicity on a single scale, and using frontier molecular orbital data to access values. A correlation of IRI with Mayr s E and N parameters is also described. 

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