Direct functionalizations acetate

The polymerization of sucrose derivatives (esters, ethers, acetals) bearing a carbon-carbon double bond has been studied (Scheme 45). Polymers can be obtained by polymerization or copolymerization.146,404 414 The monomers are prepared either by multistep synthesis, leading to defined compounds and subsequently rather well-controlled polymerization processes,302,415,416 or by direct functionalization of unprotected sucrose, leading to mixtures of isomers and... 

The mitosane A -oxide derivative (57) is similarly converted into the pyrroloindole derivative (58) in high yield upon reaction with acetic anhydride in chloroform (equation 17). The corresponding reaction of the 1,2-diacetoxy derivative (59) is more complex, however, as there is no directing functionality to orient the reaction (Scheme 11). One of the reaction products (62) is viewed as being formed via intermediates (60) and (61). If this mechanistic rationale is correct then the transformation of (59) to (62) represents a new manifestation of the Polonovski reaction. 

Ionomers of practical interest have been prepared by two synthetic routes (a) copolymerization of a low level of functionalized monomer with an olefinically unsaturated monomer or (b) direct functionalization of a preformed polymer. Typically, carboxyl containing ionomers are obtained by direct copolymerization of acrylic or methacrylic acid with ethylene, styrene and similar comonomers by free radical copoly-merization. Rees (22) has described the preparation of a number of such copolymers. The resulting copolymer is generally available as the free acid which can be neutralized to the degree desired with metal hydroxides, acetates and similar salts. Recently, Weiss et al.(23-26) have described the preparation of sulfonated ionomers by copolymerization of sodium styrene sulfonate with butadiene or styrene. 

The preparation of ionomers involves either the copolymerization of a functionalized monomer with an olefinic unsaturated monomer or direct functionalization of a preformed polymer. Typically, free-radical copolymerization of ethylene, styrene, or other a-olefins with acrylic acid or methacrylic acid results in carboxyl-containing ionomers. The copolymer, available as a free acid, is then neutralized partially to a desired degree with metal hydroxides, acetates, or similar salts. The second route for the preparation of ionomers involves modification of a preformed polymer. For example, sulfonated polystyrene is obtained by direct sulfonation of polystyrene in a homogeneous solution followed by neutralization of the acid to the desired level. Some commercially available ionomers are listed in Table 15.17. 

Direct functionalization of the C2 position of thiophene can be accomplished through an oxidative-Heck reaction employing palladium(II) acetate in the presence of silver carbonate. The resulting products are obtained in good to high yields with the trans-alkene isomer being favored. Typically less than 10% branched coupling products were observed (not shown). ... 

Functionalization of Furazan. 1,2,5-Oxadiazole belongs to the broader class of furazans that are known to possess potent biological activities. Although this class of compounds are well explored, little is known about direct functionalization of 1,2,5 oxadiazole to access its substituted congeners, which are usually synthesized from their corresponding substituted glyoxime derivatives. Neat 1,2,5-oxadiazole reacts with methyl diazoacetate in the presence of cupric stearate to form 4-methoxycarbonylmethyl 1,2,5-oxadiazole in 12% isolated yield (eq 2). It should be noted that the reaction does not proceed with the use of rhodium acetate. 

As the direct functionalization of 130e-g failed, the precursor 62b was converted to the corresponding diacetoxymethyl derivative 134a with Pb(OAc)4 in acetic acid in a 52 % yield (Scheme 5.31). The latter then reacted with efliyl... 

The N-oxide function has proved useful for the activation of the pyridine ring, directed toward both nucleophilic and electrophilic attack (see Amine oxides). However, pyridine N-oxides have not been used widely ia iadustrial practice, because reactions involving them almost iavariably produce at least some isomeric by-products, a dding to the cost of purification of the desired isomer. Frequently, attack takes place first at the O-substituent, with subsequent rearrangement iato the ring. For example, 3-picoline N-oxide [1003-73-2] (40) reacts with acetic anhydride to give a mixture of pyridone products ia equal amounts, 5-methyl-2-pyridone [1003-68-5] and 3-methyl-2-pyridone [1003-56-1] (11). 

Alternating equimolar copolymers of vinyl acetate and ethylene and alternating copolymers of vinyl acetate and acrylonitrile have been reported (127,128). Vinyl acetate and certain copolymers can be produced directly as films on certain metallic substrates by electroinitiation processes in which the substrate functions as one electrode (129). 

The other analytical methods necessary to control the typical specification given in Table 5 are, for the most part, common quality-control procedures. When a chemical analysis for purity is desired, acetylation or phthalation procedures are commonly employed. In these cases, the alcohol reacts with a measured volume of either acetic or phthalic anhydride in pyridine solution. The loss in titratable acidity in the anhydride solution is a direct measure of the hydroxyl groups reacting in the sample. These procedures are generally free from interference by other functional groups, but both are affected adversely by the presence of excessive water, as this depletes the anhydride reagent strength to a level below that necessary to ensure complete reaction with the alcohol. Both procedures can be adapted to a semimicro- or even microscale deterrnination. 

The ability to convert a protective group to another functional group directly without first performing a deprotection is a potentially valuable transformation. Silyl-protected alcohols have been converted directly to aldehydes, ketones, bro-mides, acetates, and ethers without first liberating the alcohol in a prior deprotection step. 

Perfluoroalkylation can be accomplished via direct reaction of peifluoroalkyl halides and copper with aromatic substrates [232, 233, 234, 235, 236] Thus, perfluoroalkyl iodides or bromides react with functionalized benzenes m DMSO m the presence of copper bronze to give the corresponding perfluoroalkylated products directly in moderate to good yields [233] (equation 157) Mixtures of ortho, meta, and para isomers are obtained [232, 233], The use of acetic anhydride as solvent gives similar results [234, 235], Similarly, the direct reaction of perfluoroalkyl iodides and pyrroles with copper metal regiospecifically gives the 2-perfluoroalkylpyrroles [236] (equation 158). 

Two different sets of experimental conditions have been used. Buu-Hoi et al. and Hansen have employed the method introduced by Papa et using Raney nickel alloy directly for the desulfurization in an alkaline medium. Under these conditions most functional groups are removed and this method is most convenient for the preparation of aliphatic acids. The other method uses Raney nickel catalysts of different reactivity in various solvents such as aqueous ammonia, alcohol, ether, or acetone. The solvent and activity of the catalyst can have an appreciable influence on yields and types of compounds formed, but have not yet been investigated in detail. In acetic anhydride, for instance, desulfurization of thiophenes does not occur and these reaction conditions have been employed for reductive acetylation of nitrothiophenes. Even under the mildest conditions, all double bonds are hydrogenated and all halogens removed. Nitro and oxime groups are reduced to amines. 

However, for the preparation of derivatives which contain a functional group directly attached to position 6, the application of the foregoing cyclization method is considerably limited by the availability or existence of the required derivatives of -keto acids and may also be affected by differences in their reactivity. Cyclization of thiosemicarbazones was, therefore, used for these substances only in the case of the 6-carboxylic acid (see also Section II,B,2,a). Of the other derivatives known, the 6-acetic acid ester should be mentioned. Recently some further derivatives of dioxotriazine-6-carboxylic acid were reported. ... 

It yields a phenylurethane melting at 41°, a semi-carbazone melting at 219° to 220°, and an oxime melting at 125°. The OH group appears to possess alcoholic as well as phenolic functions, forming acetic and benzoic esters, as well as direct combinations with alkalis. 

The reactivity of the bromo and amino functions in 4-bromo-l//-3-bcnzazepin-2-amine (8) has been investigated thoroughly.15-41 Acetylation with acetic anhydride at room temperature proceeds normally to give A%icetyl-4-bromo-17/-3-benzazepin-2-amine (72% mp 171 — 173CC), whereas in refluxing acetic anhydride, the diacetyl derivative 9 is produced. In each instance, the acetylated products are isolated by removal of the excess acetic anhydride and crystallization of the residue from a suitable solvent. If, however, the acetylation mixtures are quenched directly with water then only ring-opened products are formed.15... 

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