Poly substitution reactions

Table VII lists the comparatively few di- or poly-substitution reactions that have been performed on dibutylstannylene acetals and tributylstannyl ethers of compounds containing cis-diols. Figure 40 (page 103) shows some of the...

Ketones that possess active methyl or methylene groups at both a-positions can undergo poly substitution reactions as exemplified by the Vilsmeier-Haack reaction of dibenzyl ketone (95), which affords 3,5-diphenylpyrone (96 35%). Products of polysubstitution are also observed in the Vilsmeier-Haack... 

In addition to providing fully alkyl/aryl-substituted polyphosphasenes, the versatility of the process in Figure 2 has allowed the preparation of various functionalized polymers and copolymers. Thus the monomer (10) can be derivatized via deprotonation—substitution, when a P-methyl (or P—CH2—) group is present, to provide new phosphoranimines some of which, in turn, serve as precursors to new polymers (64). In the same vein, polymers containing a P—CH group, for example, poly(methylphenylphosphazene), can also be derivatized by deprotonation—substitution reactions without chain scission. This has produced a number of functionalized polymers (64,71—73), including water-soluble carboxylate salts (11), as well as graft copolymers with styrene (74) and with dimethylsiloxane (12) (75). 

Poly(phenylene oxide)s undergo many substitution reactions (25). Reactions involving the aromatic rings and the methyl groups of DMPPO include bromination (26), displacement of the resultant bromine with phosphoms or amines (27), lithiation (28), and maleic anhydride grafting (29). Additional reactions at the open 3-position on the ring include nitration, alkylation (30), and amidation with isocyanates (31). 

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. 

The nucleophilic aromatic substitution reaction for the synthesis of poly(arylene ether ketone)s is similar to that of polysulfone, involving aromatic dihalides and aromatic diphenolates. Since carbonyl is a weaker electron-withdrawing group titan sulfonyl, in most cases, difluorides need to be used to afford high-molecular-weight polymers. Typically potassium carbonate is used as a base to avoid the... 

In addition to nucleophilic and electrophilic substitution reactions, other reactions have also been used to prepare poly(arylene edier)s, especially those with special structures which otherwise could not be prepared. The following paragraph briefly reviews these reactions. 

The Ullman reaction has long been known as a method for the synthesis of aromatic ethers by the reaction of a phenol with an aromatic halide in the presence of a copper compound as a catalyst. It is a variation on the nucleophilic substitution reaction since a phenolic salt reacts with the halide. Nonactivated aromatic halides can be used in the synthesis of poly(arylene edier)s, dius providing a way of obtaining structures not available by the conventional nucleophilic route. The ease of halogen displacement was found to be the reverse of that observed for activated nucleophilic substitution reaction, that is, I > Br > Cl F. The polymerizations are conducted in benzophenone with a cuprous chloride-pyridine complex as a catalyst. Bromine compounds are the favored reactants.53,124 127 Poly(arylene ether)s have been prepared by Ullman coupling of bisphenols and... 

Smith, Jason A., 431 Sn2+ compounds, 233 Sn4+ compounds, 232 SNAr reaction. See also Nucleophilic aromatic substitution reaction poly(arylene ether sulfone) synthesis via, 336-340... 

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... 

Molecular structural changes in polyphosphazenes are achieved mainly by macromolecular substitution reactions rather than by variations in monomer types or monomer ratios (1-4). The method makes use of a reactive macromolecular intermediate, poly(dichlorophosphazene) structure (3), that allows the facile replacement of chloro side groups by reactions of this macromolecule with a wide range of chemical reagents. The overall pathway is summarized in Scheme I. 

The nucleophilic substitution on poly(vinyl chloroformate) with phenol under phase transfer catalysis conditions has been studied. The 13c-NMR spectra of partly modified polymers have been examined in detail in the region of the tertiary carbon atoms of the main chain. The results have shown that the substitution reaction proceeds without degradation of the polymer and selectively with the chloroformate functions belonging to the different triads, isotactic sequences being the most reactive ones. 

The chemical modification of poly (2,6-dimethyl-l,4-phenylene oxide) (PPO) by several polymer analogous reactions is presented. The chemical modification was accomplished by the electrophilic substitution reactions such as bromination, sulfonylation and acylation. The permeability to gases of the PPO and of the resulting modified polymers is discussed. Very good permeation properties to gases, better than for PPO were obtained for the modified structures. The thermal behavior of the substituted polymers resembled more or less the properties of the parent polymer while their solution behavior exhibited considerable differences. 

In addition to providing many new precursors to functionalized poly(alkyl/arylphosphazenes), the deprotonation/substitution reactions of these N-silylphosphoranimines serve as useful models for similar chemistry that can be carried out on the preformed polymers. New reactions and experimentation with reaction conditions can first be tried with monomers before being applied to the more difficult to prepare polymeric substrates. A considerable amount of preliminary work [e.g., with the silylated monomers (z z) and polymers (2 o) has demonstrated the feasibility of this model system approach. 

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. 

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. 

Simple Substitution Reactions with Poly(dlhalophosphazenes)... 

Alkyl and aryl derivatives of poly(dichlorophosphazene) are not efficiently synthesized by nucleophilic reaction of LXXXIV with metal alkyls or aryls. The halogen substitution reaction occurs but is accompanied by polymer chain cleavage. Use of poly(difluorophosphazene) or introduction of aryl and alkyl groups at the monomer stage offer some improvement, but neither method is fully satisfactory. The best route to alkyl and aryl derivatives is polymerization of A-(trimethylsilyl)-/).P-dialkyl-.P-halophosphoranimines at moderate temperatures (25-60°C) in the presence of a Lewis acid [Allcock et al., 1996, 2000, 2001a,b Neilson and Wisian-Neilson, 1988]. The reaction proceeds as a cationic chain polymerization ... 

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]. 

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. 

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