Reactivity Mayr scale

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... 

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... 

Mayr, H. (2001) Reactivity scales posters. Available at bttp //www.cup.lmu.de/oc/ mayr/C DmayrPoster.btml. 

We might ask just how reactive indole is in comparison with other aromatic rings. Mayr and his coworkers have carried out extensive studies on relative nucleophi-licity, N, by examining reactivity towards a series of benzhydryl carbocations [1]. In this comparison, indole was found to have the relative reactivity 5.55. The 1 -methyl (5.75) and 1,2-dimethyl derivatives are more reactive, while 2-methylindole is somewhat less reactive (4.42) because of its steric effects [2]. Pyrrole is less reactive with an N value of 4.63. Indole is substantially less reactive than representative enamines, such as 1-pyrrrolidinocyclohexene, for which N is 14.91 [3]. Being a logarithmic scale, this indicates that indole is some 15 times more reactive than pyrrole, but 10 ° less reactive than the cited enamine. For simpler aromatics, 1,3-dimethoxybenzene is assigned an N value of 2.48 and toluene, —4.47 Thus, indole is about 10 ° more reactive than toluene. 

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]. 

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. 

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. 

Several SNl-type reactions can be now rationally designed through the use of the Mayr scales of reactivity [9]. To design a new reaction of carbocations it is quite... 

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