Substitution by alkoxy

The telluraxanthylium salts 92 readily add pyridine at position 9 to give salts 112 (89KGS691). The pyridinium cation behaves as a good nucleofugal group prone to substitution by alkoxy groups when salts 112 are treated with alcohols. 

Halogenation of sp3 or sp2 carbon inhibits abstraction and addition reactions by factors of 10 or more, whereas substitution by alkoxy groups or conjugation of two or more double bonds increases rates by factors of 10-100 (Hendry et al., 1974). Thus furans are both conjugated and oxygen substituted, leading to rapid oxidation. 

The reaction was extended to 1,3-dienyltins, giving the corresponding lithiated reagents, both in terminal633-635 or internal636 position, which can be substituted by alkoxy groups637. Recently, a 1,3,5-trienyl lithium carbanion was prepared in a similar way from 22 and used for a further synthesis (equation 48)638. 

Chlorine atoms in pyrimido[5,4-tf(]pyrimidines can also be substituted by alkoxy or aroxy,213 214i 220-226-222-233-234- atl(j lkylsuifanyl or sulfanyl groups.214,224,226 228 Thus, the reaction of tri- or tetrachloropyrimido[5,4-ef]pyrimidines with sodium methoxide at room temperature gives the corresponding methoxy product 6.213,226... 

The sulfanyl and alkylsulfanyl group has been substituted by alkoxy, amino, hydrazino and hydroxyamino groups85 233 239,242 243 and has also been oxidized to the alkylsulfonyl group which was then replaced by an amino group.233... 

PTs P-substituted by alkoxy and aryolxy groups have been synthesized from symmetrical bithiophenes 15 and 16. The position of the substituents proves to be crucial for the polymerization processes [64]. Bithiophene 15 substituted at the inner P-positions leads only to short-chain oligomers [64,65]. By contrast, substitution at the outer P-positions leads to a straightforward electropolymerization. As shown by electrochemical and theoretical studies, this latter mode of substitution contributes to enhance the density of unpaired electron at the coupling a-position [65]. 

Only a few papers describe the polymerization of unsaturated monomers with a covalent M-O bond. Ziegler-Natta copolymerization of the diisobutylaluminium-alkoxy-isopren derivative 35 with butadiene occurs by a neodynium catalyst in a hydrocarbon solvent [180]. Mainly the monomer 35 in, A-cis configuration is found in the copolymer. A chiral monomer based on ethyleneglycolmonomethacrylat being substituted by alkoxy derivatives of Ti(IV) and different chiralic substituents was polymerized [181]. Such polymers are interesting as chiralic catalysts. 

A perfluoroalkyl group activates fluorine atom in 2-fluoro-3-trifluoromethylfurans to nucleophilic substitution with a broad range of nucleophiles [102-105]. Huorine can be efficiently substituted by alkoxy or phenoxy groups, aliphatic or heterocyclic thiols and amines or reduced with lithium aluminium hydride. The C-nucleophiles like cyanide or malonate anion as well as phenylithium and phenylmagnesium bromide can also be involved into the reaction. 

The phosphite efficiency in hydroperoxide reduction decreases in the order phosphites > alkyl phosphites > aryl phosphites > hindered aryl phosphites. Hindered aryl phosphites can also act as chain breaking primary antioxidants when substituted by alkoxy radicals but their activity is lower than that of hindered phenols but in oxidizing media at high temperatures the hydrolysis of aryl phosph(on)ites takes place and produces hydrogen phosph(on)ites and phenols which are effective chain-breaking antioxidants. Multifunctional stabilizers such as those containing HAS-phosph(on)ites moieties show a superior efficiency due to the intramolecular synergism—Table 6 [49]. 

Ph) or OPh, the last two of which may be substituted by up to three groups selected from alkyl, alkoxy, sulfonate, carboxylate, alkylthio-,... 

Another remarkable reaction is the nucleophilic substitution of the chlorine by alkoxy or sulfido groups using the alcohol or the thiol and the weak base Na2C03 in situ. For example, in the case of ethanol, the reaction proceeds in 12 h at reflux Eq. (23), Table 3. 

In fluorinated alcohols such as 2,2,2-trifluoroethanol and 1,1,1,3,3,3-hexafluoro-isopropanol, only alkoxy-de-diazoniation and substitution by the anion of the diazonium salt are observed (Sec. 8.3), because these alcohols are extremely weak nucleophiles. 

Ethers may be prepared by (1) dehydration of alcohols and (11) Williamson synthesis. The boiling points of ethers resemble those of alkanes while their solubility Is comparable to those of alcohols having same molecular mass. The C-O bond In ethers can be cleaved by hydrogen halides. In electrophilic substitution, the alkoxy group activates the aromatic ring and directs the Incoming group to ortho and para positions. 

Some reactions of 2,2 -bipyridine /V-oxides have been reported. The l,T-dioxide is nitrated readily to 4,4 -dinitro-2,2 -bipyridine 1,T-dioxide. ° ° °" 2,2 -Bipyridine 1-oxide is also nitrated in the 4 position. The nitro groups in 4,4 -dinitro-2,2 -bipyridine l,T-dioxide are reactive, being replaced by chlorine with concentrated hydrochloric acid," by bromine with acetyl bromide, by hydroxyl with dilute sulfuric acid, and by alkoxy groups with sodium alkoxides. Some of the dialkoxy derivatives are useful catalysts for the oxidation of aromatic compounds. The dinitro dioxide is deoxygenated to 4,4 -dinitro-2,2 -bipyridine with phosphorus trichloride in chloroform, and other substituted l,T-dioxides behave similarly, but with phosphorus trichloride alone, 4,4 -dichloro-2,2 -bipyridine results. The dinitro dioxide is reduced by iron powder in acetic acid to 4,4 -diamino-2,2 -bipyridine, whereas 4,4 -dichloro-2,2 -bipyridine l,T-dioxide is converted to its 4,4 -diamino analogs with amines. Related reactions have been described. ... 

We have shown that alanes substituted with alkoxy and siloxy ligands can be used very efficiently in CVD processes, either producing single ceramic phases or mixtures of several phases using only one single precursor molecule. As the processes discussed above are driven by chemical reactions within distinct molecules or in between two molecules, the phases formed are... 

Syntheses of simple diols are described first, followed by a multistep synthesis of ribose. These syntheses illustrate the compatibility of alkoxy substituents on boronic esters with their reaction with (dihalomethyl)lithium. The limitations of this compatibility, as well as failure of a (chloro-allyl)boronic ester to undergo substitution by alkoxides, are also noted. Retention of configuration of the migrating group is a consistent and repeated feature of these syntheses. 

Whatever the precursor, the formation of an intermediate solid phase was always observed. It can be inferred from X-ray diffraction (Fig. 9.2.7) and infrared spectroscopy that this intermediate phase shows a lamellar, incompletely ordered structure (turbostratic structure) built up with parallel and equidistant sheets like those involved in the lamellar structure of the well-crystallized hydroxides Ni(OH)2 or Co(OH)2, these sheets are disoriented with intercalation of polyol molecules and partial substitution of hydroxide ions by alkoxy ions (29). The dissolution of this solid phase, which acts as a reservoir for the M(I1) solvated species, controls the concentration of these species and then plays a significant role in the control of the nucleation of the metal particles and therefore of their final morphological characteristics. For instance, starting from cobalt or nickel hydroxide as precursor in ethylene glycol, the reaction proceeds according to the following scheme (8) ... 

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