Poly , substituted

There have been many studies of the orientation of nitration in di- and poly-substituted derivatives of benzene, but in very few cases have... 

In comparing the reactivity at different positions in a heterocycle, a poly-substituted derivative is sometimes used with the idea that selective reaction of the same leaving group at different positions in a single molecule gives the most clear-cut answer. However, in a polychloroazine, the mutual activation of the chlorines by one another is not identical (unless the molecule is symmetrical, in which case the... 

An important side reaction is the formation of diaryl methane derivatives ArCHaAr. Moreover poly substituted products may be obtained as minor products. Aromatic compounds have been treated with formaldehyde and hydrogen bromide or hydrogen iodide instead of hydrogen chloride. The formaldehyde may be replaced by another aldehyde the term Blanc reaction however stands for the chloromethylation only. 

Product distrihution among the chloromethanes depends primarily on the mole ratio of the reactants. For example, the yield of mono-chloromethane could he increased to 80% hy increasing the CH4/CI2 mole ratio to 10 1 at 450°C. If dichloromethane is desired, the CH4/CI2 ratio is lowered and the monochloromethane recycled. Decreasing the CH4/CI2 ratio generally increases poly substitution and the chloroform and carhon tetrachloride yield. 

The same reaction, carried out with conventional heating at the same temperature, took more that 6 h to give comparable yields of the products. Dihydropyrazoles were also obtained by microwave-assisted reaction of poly-substituted vinyl ketones 122 with hydrazines, followed by reaction of the unstable pyrazole 123 with electrophiles (Scheme 43) [80]. 

Since thiophene derivatives, heterocyclic aromatic compounds, are sensitive toward electrophilic substitution reactions, the bromination of these compounds generally gives a mixture of mono-, di-, and other poly-substituted bromination products (ref. 19). However, we have recently found that BTMA Br3 is a useful... 

In a series of papers culminating in the report of a total synthesis of hemibrevetoxin B, Nakata and co-workers utilised a zinc catalysed ring expansion of poly-substituted tetrahydropyrans, exemplified by the transformation of 34 to 35 (Scheme 7) <96TL213, 96TL217, 96TL6365>. 

Gregory, P. Thetford, D. (Zeneca). Poly-Substituted phthalocyanines. U S Patent 5486,274, January 23, 1996. 

The Sn—Sn bond in the azadistannirane B is unusually short while most of the other ring values are normal. The enlarging effect of t-butyl and poly substituted phenyls persists in the rings. 

A Ni(dppe)Br2-Zn system effectively catalyzes co-cydotrimerization of an allene with a propiolate. The reaction is highly regio- and chemoselective to afford a poly-substituted benzene derivative in good yield. (Scheme 16.82) [92], From the observation that no desired [2 + 2 + 2] product is obtained for the reaction of 1-hexyne and phenylacetylene with w-butylallene under similar conditions, the presence of an electron-withdrawing C02Me group in the alkyne moiety is essential for the success of the present [2 + 2 + 2]-co-cyclotrimerization. 

Apparently, the aromatization of the heterocyclic cation serves as a driving force of the Cope rearrangement in the transformation of the 3-formyl-4-allyl-4//-pyrane (481) into poly-substituted pyrylium salt 483 which presumably proceeds via 482 (equation 183)242. 

Free electron pairs are a good source for an electron which is to be ejected and therefore, the IE of ethanol and dimethylether is lower than that of ethane. It has been shown that the IE of a poly-substituted alkane is almost the same as the IE of the structurally identical mono-substituted alkane which has the lowest value. [27] The other substituent, provided it is separated by at least two carbon atoms, exerts a very small effect upon the IE, e.g., the IE of dimethylsulfide, CH3SCH3, 8.7 eV, is almost the same as that of methionine, CH3SCH2CH2CH(NH2)COOH. Introduction of an oxygen decreases the IE less than nitrogen, sulfur or even selenium do, since these elements have lower electronegativities and thus, are even better sources of an electron. 

Production of pol3rmers through poly-substitution or poly-condensation reactions would be expected to be a natural extension of simple PTC chemistry. To a large extent this is true, but as Percec has shown. Chapter 9, the ability to use two-phase systems for these reactions has enormously extended the chemist s ability to control the structure of the polymers produced. Kellman and co-workers (Chapter 11) have also extensively studied poly-substitution displacements on perfluorobenzene substrate to produce unique polymers. 

Effects of single, isolated substituents on physical properties, reactions, or equilibria can be treated successfully on the basis of dual substituent parameter (DSP) approaches. To deal with di- or poly-substituted systems is less straightforward. Here the question arises of how individual substituents combine their respective actions. It is in this context that the captodative substituent effect has to be seen. 

The chair conformation is the preferred conformer for the oxane ring and substituted derivatives. In the case of poly-substitution (e.g., 1,3-diaxial groups), twist conformers can also participate in the equilibrium. Substituents can adopt the axial and equatorial positions ring interconversion between the chair conformers is fast on the NMR timescale at ambient temperature but becomes slow at low temperature (AG = 10.3 kcal mol- ) (73JA4634). 

The spectra are clearer in substituted compounds, especially in para-and poly-substituted aromatic systems. In the former case sign determination is feasible and McFarlane has obtained the values for some typical compounds as shown in Table XXII the data (without signs) for the tris(4-fluorophenyl)phosphine oxide are also included. 

Intramolecular displacement by a benzyloxy group to form a tetrahydrofuran ring with concomitant debenzylation has been recognized as an undesired side reaction [111, 112] but is also useful in stereocontrolled formation of poly-substituted tetrahydrofurans [111, 113]. 

Trimethyl Benzene under Disubstituted and Poly substituted Benzene Hydrocarbons... 

Phenylation of quinoline with benzoyl peroxide is easier (qpl,nR 5.0) than that of pyridine (71BSF2612). Substitution takes place at all carbons, and partial rate factors (F2 = 3.3, F3 = 1.8, F4 = 5.4, Fs = 6.6, F6 = 1.5, F7 = 1.6, F8 = 9.6) were obtained at 1% conversion. Homolytic arylation of quinoline is not of much synthetic value as reactions taken to higher conversion suffer not only from lack of selectivity, but di- and poly-substitution also take place. 

Reaction of II with electrophilic agents, HN03, SOs, and CH20 in concentrated sulfuric acid, and with bromine in acetic acid, yielded the mono- or poly-substituted complexes, depending upon the reaction conditions (16). The position of substitution in these complexes was established by permanganate oxidation to the benzoic acids, esterification of the acids with diazomethane, and sub-... 

Diarene metals generally decompose under conditions of normal electrophilic substitution, but dibenzene chromium can be metalated with amyl sodium in alkanes, and subsequent reaction with carbon dioxide and dimethyl sulfate results in a complex mixture of mono-, di-, and poly-substituted dibenzene chromium methyl esters. It is interesting that these polysubstituted compounds are homoannular in contrast to the corresponding ferrocene compounds. In view of the scanty evidence and ease of oxidation, it is impossible to conclude whether the diarene metals are less aromatic than the dicyclopentadienyl metals as predicted by simple theory (Sec. III.A). 

---