Substitution of function

Reactions involving the introduction and substitution of functional groups in the side chain of isoxazole derivatives are of synthetic value and have been used to synthesize various substituted isoxazoles. 

A large part of the chemical reactions of 1,3,2-diazaphosphole and NHP derivatives reported to date include transformations under substitution of functional substituents at the C, N, or P ring atoms. The interest in several of these displacement processes was mainly directed by the desire to develop synthetic pathways for specifically... 

Table 22.1), which has been modified by appropriate substitutions to yield the desired molecule. Thus, aliphatic hydrocarbons can be built up from methane by repeated substitutions of methyl groups for hydrogen atoms. Other compounds are formed by substitution of functional groups for CHn groups. The heat capacity constants are those for a cubic polynomial in the temperature, which are similar to those discussed in Chapter 4. 

TABLE 22.7. Corrections for Type Number and Multiple Substitutions of Functional Groups... 

Tricarbonyliron-coordinated cyclohexadienylium ions 569 were shown to be useful electrophiles for the electrophilic aromatic substitution of functionally diverse electron-rich arylamines 570. This reaction combined with the oxidative cyclization of the arylamine-substituted tricarbonyl(ri -cyclohexadiene)iron complexes 571, leads to a convergent total synthesis of a broad range of carbazole alkaloids. The overall transformation involves consecutive iron-mediated C-C and C-N bond formation followed by aromatization (8,10) (Schemes 5.24 and 5.25). 

The toxicity of the paraffins is altered with the substitution of functional groups see figure 6.15. The ranking of the toxicity of the methyl derivatives is... 

The preparation of particular 1,3,4-oxadiazole derivatives by substitution of functional groups will be dealt with in Section III, A. 

The substitution of functional groups at the electrophilic double bond or catalytic replacement of the hydrogen atom of alkene fragment by pyrroles or indoles has found wide use in the synthesis of U-vinylpyrroles or -indoles. Thus, indole was reacted with ethyl 2-nitro-3-ethoxyacrylate 662 to give ethyl 2-nitro-3-(3-indolyl)acrylate 663 as a 1 1 mixture of the (E)- and (Z)-isomers (Equation 159) <1996TL3309>. 

The majority of the more important methods for the preparation of fluorinated compounds by substitution reactions have been reviewed in the previous sections. There are, however, some additional important synthetic procedures which should also be mentioned, mainly those concerned with the introduction of fluorine by substitution of functional groups containing boron, silicon and tin the reactions of organotin compounds are the most well-studied to date. These reactions are excellent synthetic methods for obtaining vinyl and aryl fluorides (sec also Section 1.1.1.1.). 

Other empirical concepts have been used to consolidate data. These include the isoelectronic principle, electronegativity correlations, the relationship to absorption spectra, and the effects of single and multiple substitutions of functional groups on molecules. A similar change in the electron affinities is observed when the more electronegative nitrogen atom replaces a CH group in aromatic molecules. Statistical techniques are used to establish these correlations. Because they are empirical and require additional data for their application, the results are less certain. 

The tyrosinase inhibitory potency of these compounds was also evaluated by the authors and attempts were made to justify their structure-activity relationships [52], Their inhibitory potential is shown in Table 3. Compound 58 was foimd to be the most potent (IC50 = 3.21 [jlM), while other compounds demonstrated moderate to potent inhibitions [52]. It was reported that the substitution of functional group(s) at the C-2 and C-3 positions and the presence of the - CH2OH group play a vital role in the potency of these compounds. Compound 58 can act as a potential lead molecule to develop new drugs for the treatment of hyperpigmentation associated with the high production of melanocytes [52]. 

I The substitution of functional groups for hydrogen in hydrocarbons creates a wide variety of organic compounds. 

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