Electrophilic tabulated

General synthetic methods were developed after 1920 and extended to many new systems. Oxidative syntheses of dyes are primarily of historical interest (1), whereas nonoxidative syntheses are the most versatile and employ varied combinations of nucleophilic and electrophilic regents. One review Hsts references for the synthesis of dyes prepared before 1959 (12), and another review provides supplemental references to more recent compounds (13). Many nucleophilic and electrophilic reagents used to synthesize cyanine and related dyes are tabulated in Reference 16. 

The hydroxy and amino groups are highly activating ortho-para-d KCtmg groups. Such compounds are attacked by all the electrophilic reagents tabulated in Scheme... 

In Taylor s tabulation of sigma values228, a+ and a for p-NCP are given identical values of 0.79228. No distinction between these two types of substituent constant is to be expected for p-N02 in connection with electrophilic aromatic substitution. Some slight distinction between them is drawn for m-N02 a = 0.72, a+ = 0.73. 

Because halogenation involves electrophilic attack, substituents on the double bond that increase electron density increase the rate of reaction, whereas electron-withdrawing substituents have the opposite effect. Bromination of simple alkenes is an extremely fast reaction. Some specific rate data are tabulated and discussed in Section 6.3 of Part A. 

The partial rate factors af and /3f for the a- and /3-positions of thiophene have been calculated for a wide range of electrophilic reactions these have been tabulated (71 AHC(13)235, 72IJS(C)(7)6l). Some side-chain reactions in which resonance-stabilized car-benium ions are formed in the transition states have also been included in this study. A correspondence between solvolytic reactivity and reactivity in electrophilic aromatic substitution is expected because of the similar electron-deficiency developed in the aromatic system in the two types of reactions. The plot of log a or log /3f against the p-values of the respective reaction determined for benzene derivatives, under the same reaction conditions, has shown a linear relationship. Only two major deviations are observed mercuration and protodemercuration. This is understandable since the mechanism of these two reactions might differ in the thiophene series from the benzene case. 

The former procedure has been used for correlating the reactivities towards electrophiles of monosubstituted thiophenes. Good cr+ plots have been obtained. The p-values for the different reactions in thiophene and benzene have been tabulated (Table 2) (71AHC(13)235, 72IJS(C)(7)6l). 

Lithiated selenophenes and tellurophenes have been used as intermediates in the preparation of a wide range of derivatives. A comprehensive tabulation of these transformations is available (790R(26)l) and this illustrates the large number of electrophiles which have been reacted with selenienyl- and, to a lesser extent, tellurienyl-lithiums. An extension of the synthetic potential of these lithiated derivatives is achieved by first converting them into iodonium salts (111), which may then be reacted with nucleophiles (Scheme 12) (74SC63). 

Reactions of amides have been extensively reviewed and tabulated.1 The most commonly encountered classes of reactions involve electrophilic attack on the nitrogen lone pair(s) or metal-nitrogen 7r-bond. 

In 1959, four independent and simultaneous reports defined the problem, van Bekkum et al. (1959), not distinguishing among the ordinary and electrophilic side-chain reactions, showed the o--constants to be broadly variable. They tabulated the a-parameters for twelve groups as derived from each reaction of an extended series. Just as illustrated in Fig. 50 for the p-methoxy, p-methyl, and p-chloro substituents, they detected extensive variations in the apparent values of the constants. The authors concluded that the postulation of two or three sets of -constants could not be regarded as sound. By eliminating all those reactions involving important resonance contributions Wepster and his associates (van Bekkum et al., 1959) obtained a series of reactions similar to those presented in Table 23, and hence derived a series of normal, an, parameters for meta and para substituents. These normal values, presumably representing the reactions for which the Hammett relationship is most precise, exhibit standard deviations of 10-30%. 

Branching at the Electrophilic Center. The data indicate that branching at the a-carbon on the substrate tends to reduce differences in reactivity between sulfur nucleophiles and H20. This conclusion is based upon the following trends among the tabulated data. 

Protecting groups have been mentioned occasionally in previous chapters in this chapter the ideas behind their use are systematically presented and a collection of protecting groups suitable for a range of functional groups is tabulated. Protection allows us to overcome simple problems of chemoselectivity. It is easy to reduce the keto-ester I to the alcohol 2 with a nucleophilic reagent such as NaBHU that attacks only the more electrophilic ketone. 

The electrophilicity index for, among others, the parent azete has been tabulated for two different models of the energy-electron number relationships <1999JA1922>. The electrophilicity index in the ground state parabola model and the electrophilicity index in the valance state parabola model tovs are reported as ajgs = tcvs/2 = 1.91. 

Reaction of 1,2,3-thiadiazoles with electrophiles has not been extensively studied, so effects of ring substituents have not been tabulated. Reaction of 1,2,3-thiadiazoles with acyl halides or metal ions has not even been reported. 

Whitesell and Whitesell" have tabulated some of the many types of electrophilic reagents that C-al-kylate metallated imines. These are potent nucleophiles and undergo substitution reactions even with weakly electrophilic species such as epoxides and oxetanes. Lithiated ketimines and aldimines have been frequently used in reactions with alkylating agents containing latent 2-keto (or aldehydo) groupsor 3-keto (or aldehydo) groups. ... 

The synthesis of model compounds to verify the structures of xenobiotic amino acid adducts (products of nonenzymatic reactions of electrophilic xenobiotics with amino acids In proteins) are Included. Methods for synthesis of some rarely observed conjugate types will be briefly Introduced. The major organic methods for synthesis are exemplified and xenobiotic conjugates prepared via these reactions are tabulated with references to the original publications. 

The reactivity of the amine as a polymerization accelerator depends upon the a+ value of the meta- or para-substituent of the amine, where a+ is the electrophilic substituent parameter previously described and tabulated (23). When the kinetic rate constant (or the reciprocal of the polymerization time with amine and peroxide initial concentrations held constant) is plotted against the a+ value on a semi-logarithmic plot (Figures 1 and 2), an inverted "V" shaped curve results. The kinetic data for Figure 1 were taken from a published article describing the polymerization of methyl methacrylate in the presence of BP and various tertiary aromatic amines as shown in Figure 2 ( 5). ... 

Studies on the radical cations of vinyl sulfides are rather scarce. The first anodic oxidation potentials of vinyl sulfides 90-94 [220-222] are tabulated in Table 6 and are irreversible. Linear correlation of substituted-phenyl vinyl sulfides 90, listed in the last column of Table 6, performs well with o+ but less well with o. Since electrophilic additions to substituted-phenyl vinyl sulfides correlate better with <7 than cr+, it has been suggested [221] that o+ vs o correlation can be used to distinguish electron transfer from electrophilic reactions. 

Polar substituents can be handled without protection because nonpolar radicals are involved as reactive intermediates. This saves steps for protection and deprotection that are necessary when substrates with such substituents are submitted to reactions where strong bases, nucleophiles and electrophiles are involved. Together with the availability of a wide variety of carboxylic acids, this method of homocoupling is a unique and attractive method for the construction of symmetrical compounds. A great number of homocoupling reactions have been tabulated in refs. [2, 25, 26]. Table 2 and molecular structures 8-17 show some selected examples. 

Much of the relative reactivity data on 1,3-DPCA reactions has been tabulated and discussed in reviews by R. Huisgen, a pioneer researcher in the field.Some representative data are presented in Table 10.3. The dipolarophiles are shown in decreasing order of electrophilicity. The data from these monosubstituted dipolarophiles should be relatively free of steric influences on reactivity. Note that for phenyl azide and benzonitrile oxide, reactivity is at a minimum for unfunctionalized alkenes and is increased by both donor and acceptor substituents. 

In order to probe the effect of the substrate amine structure on this chemistry forming carbamates, a series of reactions were run under identical conditions to those described for Table I using benzyl chloride as the electrophile and tetramethylcyclohexyl guanidine as the co-base. The reaction rates are tabulated as relative rates with the rate for n-octyl amine set as 1. The results are summarized in Table II. 

Some final examples of the Makosza indole synthesis are tabulated in Table 2. Volovenko and colleague report a simple synthesis of 3-substituted-2-amino-5-nitroindoles (entry 1), which were transformed into pyrimido[l,2-fl] indoles upon reaction with p-dicarbonyl compounds [26]. A conventional VNS method was used by Lerman and colleagues to craft 6- and 7-hydroxyindoles via sacrificial chlorine atoms that serve to increase the electrophilicity of the benzene ring toward cyanomethylation. Subsequent transfer hydrogenation (Pd/C/HCO NH ) gives the respective hydroxyindoles (entries 2, 3) [27], The preparation of 3,6-dimethyl-5-methoxyindole by Skibo and coworkers (entry 4) was the starting point in a synthesis... 

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