Reactions, with cyclic anhydrides

Halo-lactonization of ketophosphoranes has been achieved via reaction with cyclic anhydrides and subsequent halogenation. " The products, halo enol lactones (75), are synthetically useful compounds, and an alternative synthesis via incorporation of the halogen at the ylid stage is also described. Mechanistic investigation of the Wittig reactions involved reveals subtle variations in pathway, allowing optimum experimental conditions to be selected to allow for the variation in reactivity of different anhydrides and halides. 

The reaction with cyclic anhydrides of dicarboxylic acids results in the formation of imidocarbamates [26-28] (Scheme 7). 

Cyclic 1,3-diacetoxy-l,3-dienes can be generated in situ from cyclic 1,3-diketones under the influence of isopropenyl acetate. The dienes then undergo Diels-Alder reactions with maleic anhydride giving as products 1-acetoxybicycloalkane dicarboxylic anhydride derivatives (10). The procedure is also successful with cyclic 1,2- and 1,4-diketones as well as cyclic a,j3-unsaturated ketones. The products, after hydrolysis to... 

The reactivity of hydrido(ethoxo) complex 4 was examined (Scheme 6-15) [8]. Metatheses similar to those postulated for alcohol exchange (Eq. 6.5) occurred between HCl, LiCl, phenyl acetate or primary amines and yielded complexes 94. The reaction of 4 with cyclic anhydrides proceeded similarly to give iridium-assisted ring opening products 95. Heterocumulenes afforded the inserhon products 96 into the Ir-O bond. 

Reactions of wood with cyclic anhydrides do not yield a by-product, leaving the modified wood polymers with a covalently bonded carboxylic group an example is reaction with succinic anhydride (SA) (Figure4.1a). With reactions above 100°C there is some formation of diester observed (Figure 4.1b), resulting in cross-linking within the cell wall matrix (Matsuda, 1987). 

This reaction, similar in scope and mechanism8S2 to 0-52, can be carried out with ammonia or primary or secondary amines.853 However, ammonia and primary amines can also give imides, in which two acyl groups are attached to the nitrogen. This is especially easy with cyclic anhydrides, which produce cyclic imides.854... 

Friedel-Crafts acylation can be carried out with cyclic anhydrides,272 in which case the product contains a carboxyl group in the side chain. When succinic anhydride is used, the product is ArCOCH2CH2COOH. This can be reduced (9-37) to A1CH2CH2CFLCOOH, which can then be cyclized by an internal Friedel-Crafts acylation. The total process is called the Haworth reaction 173... 

LiAlH4 usually reduces open-chain anhydrides to give 2 moles of alcohol, With cyclic anhydrides the reaction with LiAIH4 can be controlled to give either diols or lactones572 (see 9-41). NaBH4 in THF, with dropwise addition of methanol, reduces open-chain anhydrides to one mole of primary alcohol and one mole of carboxylic acid.573 OS VI, 482. 

Acetals are readily formed with alcohols and cyclic acetals with 1,2 and 1,3-diols (19). Furfural reacts with poly(vinyl alcohol) under acid catalysis to effect acetalization of the hydroxyl groups (20,21). Reaction with acetic anhydride under appropriate conditions gives the acylal, furfurylidene diacetate [613-75-2] (22,23). 

This article summarizes and analyzes the results obtained for the anionic copolymerization of cyclic ethers with cyclic anhydrides. This reaction is of great practical importance, especially as curing reaction of epoxy resins and is also used for the preparation of linear polyesters with special functional pendant groups. 

Hilt et al. 42,541 found by conductivity measurements that the copolymerization of epoxides with cyclic anhydrides initiated by alkali salts is of ionic character. Luston and Manasek 36,57), who used ammonium salts, came to the same conclusion. The rate of copolymerization increases linearly with rising initiator concentration (Fig. 1, the slope of the curve log k vs log c,n is unity) but only up to a limit which depends on the solubility of the initiator in the reaction system54). A rise in the copolymerization rate is accompanied by an increase in the conductivity of the reaction... 

Data on molecular weights of polyesters can provide information on the mechanism and termination and transfer reactions. As follows from section 3.2.3 the copolymerization of epoxides with cyclic anhydrides should proceed stoichiometrically without transfer or termination reactions, and the average degrees of copolymerization should only depend on the molar ratio of monomers to the initiator. Polymers with a narrow molecular Weight distribution should be obtained. 

For the copolymerization of epoxides with cyclic anhydrides and curing of epoxy resins, Lewis bases such as tertiary amines are most frequently used as initiators. In this case, terminal epoxides react with cyclic anhydrides at equimolar ratios. The time dependence of the consumption of epoxide and anhydride is almost the same for curing 35-36> and for model copolymerizations 39,40,45). The reaction is specific 39,40) to at least 99 %. In contrast, the copolymerization with non-terminal epoxides does not exhibit this high specificity, probably because of steric hindrances. The copolymerization of vinylcyclohexene oxide or cyclohexene oxide is specific only to 75-80 % and internal epoxides such as alkylepoxy stearates react with anhydrides only to 60-65 %. On the other hand, in the reaction of epoxy resins with maleic anhydride the consumption of anhydride is faster 65the products are discoloured and the gel is formed at a low anhydride conversion 39). Fischer 39) assumes that the other resonance form of maleic anhydride is involved in the reaction according to Eq. (33). 

However, the experimental data in the literature do not allow to determine the effect of the structure of the amines on the rate of copolymerization of epoxides with cyclic anhydrides, nor to verify the validity of Eq. (36) for this type of reaction. 

A reaction order of 1/2 was determined by Malavasic et al.91) for the curing of epoxy resins with cyclic anhydrides over the conversion range 18-79 %. At 86-98.5 % conversion, the authors established a first-order curing reaction. Booss and Hau-schildt90) regard copolymerization and curing as a zero-order process with respect... 

The copolymerization of epoxides with cyclic anhydrides is a thermally activated reaction. Table 6 gives a survey of the thermodynamic parameters. The activation energies determined by different authors are in good agreement and vary between 52.8 and 64.9 kJ/mol, depending on the monomer used. Exceptions are only the... 

The reaction of cyclic anhydrides with amines can be different from that with alcohols, because in the case of amines, the amido acid formed during the first step (Eq. 2.9) can close a cycle to give an imide group (Eq. 2.10) ... 

After the amines, acid anhydrides constitute the next most commonly used reagents for curing epoxy monomers. The epoxy-acid reaction proceeds through a stepwise mechanism (Sec. 2.2.4) while the reaction of epoxides with cyclic anhydrides, initiated by Lewis bases, proceeds through a chain-wise polymerization, comprising initiation, propagation, and termination or chain transfer steps. Some of the postulated reactions are shown in Table 2.25 (Matejka et al., 1985b Mauri et al., 1997). 

In starch chemistry and technology, extrusion is used for cooking as well as for preparation of starch complexes with such guest molecules as gluten6511 and lipids.651 Acylation of starch with cyclic anhydrides of dioic acids on extrusion has been demonstrated the reaction provides anionic starches.651... 

Treatment of l-methyl-2-piperidone with phenylmagnesium bromide and subsequent reaction with acetic anhydride and then water gave the acetate 21 in small yield.139 This indicates that the salt of the carbinolamine form is an intermediate which, on liberation, affords the cyclic enamine in the five- and six-membered series, for steric reasons. 

Cycloadditions. A cyclic movement of electrons can be drawn for any number of cycloadditions, but not all of them take place. Thus butadiene undergoes a Diels-Alder reaction with maleic anhydride, but ethylene and maleic anhydride do not give a cyclobutane when they are heated together. 

Compound 44 can be transformed into the cyclic imide 45 by N-methylation with diazomethane. Reaction with acetic anhydride leads to sulfdimine 46, as a product of intramolecular attack of sulfone on imide nitrogen followed by ring opening (Scheme 7 <1995CC1069>). 

In spite of a great number of studies devoted to curing with cyclic anhydrides, there existed a number of contraversial views concerning the reaction mechanism. Recent studies have revealedthat in the presence of tertiary amines the reaction can proceed also in the absence of proton donors. The tertiary amine reacts first with epoxide most probably via a zwitterion The simplified mechanism is as follows... 

Kluger, R., Hunt, J. C. Circumventive catalysis contrasting reaction patterns of tertiary and primary amines with cyclic anhydrides and the avoidance of intermediates. J. Am. Chem. Soc. 1989, 111,3325-3328. 

Condensations. Reaction of tertiary alcohols with cyclic anhydrides, Baylis-Hillman reaction, aldol reaction involving bis(trimethylsilyl) ketene acetals, reaction of R(XIH(CN)2 with activated imines, and the [2+2]cycloaddition between isocyanates and enol ethers are assisted by high pressure. 

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