Imides carbons

A common method of dihydrothiazole synthesis involves the condensation of a Cys residue with an imidateJ85 This method, however, suffers from some drawbacks (1) It does not readily lend itself to the synthesis of dihydrothiazoles substituted with groups other then a hydrogen at the C5 position because Cys residues substituted at the ((-position are not commercially available. (2) The method requires the preparation of an imidate from a peptide C-terminus, which may require several steps and sometimes leads to racemization at the carbon next to the imidate carbon. (3) The dihydrothiazole cannot be introduced into a complete peptide fragment as in Section 11.2.4.1. 

Heterocycles.2 The reagent can be used for synthesis of a variety of mono- and bicyclic heterocycles. The imidate carbon is usually the preferred center for nucleophilic attack. 

Phthalimides have often been used in the double role of electron acceptor sensitizers and radical traps, and are in fact benzylated by irradiation in the presence of toluene and several other precursors. 4,5-Dicyanophthalimide undergoes substitution of a benzyl for a cyano group when irradiated with toluene, but mainly attack at the imide carbon occurs with diphenylmethane. With various donors the competition between the two modes of reaction has been found to depend on the cage vs. out of cage radical cation cleavage, in the first case with the assistance of the radical anion [223] (Sch. 18). 

The author s work on polyimide synthesis and its use to derive MI values for polyimides has been described in the previous section [43, 45-46]. These are virtually the only strictly true mesogenic polyimides which have been reported in the literature to date. However, in addition, there have been many reports of modified copolyimides such as copoly(etherimide)s, copoly(amide-imide)s, co-poly(esterimide)s or copoly(imide-carbonate)s which are discussed below. 

Table 26. Copoly(imide-carbonate)s containing pyrromellitic dianhydride...

Treatment of the N-cyano-imidates (257) with o-hydrazinobenzoic acid gives triazolo[l,5-a]quinazolines (258). The hydrazine attacks the imidate carbon initially, rather than the nitrile group this contrasts with the preferential reaction at the nitrile function of the similar A -cyano-amidines (221) by amines (see p. 253) (Scheme 103). ... 

Alcohols, glycols, amines, amides, imines, imides carbon... 

Poly(benzoxazole-co-imide) carbon dioixde 2014KIM... 

The application of miaowave irradiation to the processing of carbon fiber-reinforced phenylethynyl-terminated polyimide composites (PETI-5/IM7) was evaluated. A miaowave process was demonstrated that fabricated unidirectional poly-imide-(carbon fiber) composites with superior thermal and mechanical properties relative to the thermal process in half the time required for the thermal process. ... 

The reaction is applicable to the preparation of amines from amides of aliphatic aromatic, aryl-aliphatic and heterocyclic acids. A further example is given in Section IV,170 in connexion with the preparation of anthranilic acid from phthal-imide. It may be mentioned that for aliphatic monoamides containing more than eight carbon atoms aqueous alkaline hypohalite gives poor yields of the amines. Good results are obtained by treatment of the amide (C > 8) in methanol with sodium methoxide and bromine, followed by hydrolysis of the resulting N-alkyl methyl carbamate ... 

Division III. Heterocyclic compounds (Heterocyclic stem nuclei). The carbon atoms are joined in closed rings which include one or more other kinds of atoms as ring components. Anhydrides and imides of dibasic acids, as well as lactones, lactams, etc. are thus included in this division... 

As we saw when discussing allylic brommation m Section 10 4 N bromosuccm imide (NBS) is a convenient free radical brommatmg agent Benzylic brommations with NBS are normally performed m carbon tetrachloride as the solvent m the presence of peroxides which are added as initiators As the example illustrates free radical bromi nation is selective for substitution of benzylic hydrogens... 

Isocyanates are derivatives of isocyanic acid, HN=C=0, ia which alkyl or aryl groups, as weU as a host of other substrates, are direcdy linked to the NCO moiety via the nitrogen atom. StmcturaHy, isocyanates (imides of carbonic acid) are isomeric to cyanates, ROCMSI (nitriles of carbonic acid), and nitrile oxides, RCMSI—>0 (derivatives of carboxyUc acid). 

The reactions of primary amines and maleic anhydride yield amic acids that can be dehydrated to imides, polyimides (qv), or isoimides depending on the reaction conditions (35—37). However, these products require multistep processes. Pathways with favorable economics are difficult to achieve. Amines and pyridines decompose maleic anhydride, often ia a violent reaction. Carbon dioxide [124-38-9] is a typical end product for this exothermic reaction (38). 

Finally, when polyamides containing four or five carbon diacids, ie, succinic acid [110-15-6] and glutaric acid [110-94-1], respectively, are heated, they form cychc imides that cap the amine ends and prevent high molecular weights from being achieved (84). For nylon-x,4, n = 1 and for nylon-x,5, n = 2. 

Polymerization by G—G Goupling. An aromatic carbon—carbon coupling reaction has been employed for the synthesis of rigid rod-like polyimides from imide-containing dibromo compounds and aromatic diboronic acids ia the presence of palladium catalyst, Pd[P(CgH )2]4 (79,80). 

Polyimides have been synthesized by Diels-Alder cycloaddition of bismaleimides and substituted biscydopentadienones (81,82). The iatermediate tricychc ketone stmcture spontaneously expeU carbon monoxide to form dihydrophthalimide rings, which are readily oxidized to imides ia the presence of nitrobenzene. 

The Michael addition of nucleophiles to the carbon—carbon double bond of maleimide has been exploited ia the synthesis of a variety of linear polymers through reaction of bismaleimide with bisthiols (39). This method has been used to synthesize ethynyl-terminated imidothioether from the reaction of 4,4 -dimercaptodiphenyl ether [17527-79-6] and A/-(3-ethynylphenyl)maleimide (40). The chemical stmcture of this Michael addition imide thermoset is as follows ... 

Virtually all of the organo derivatives of CA are produced by reactions characteristic of a cycHc imide, wherein isocyanurate nitrogen (frequendy as the anion) nucleophilically attacks a positively polarized carbon of the second reactant. Cyanuric acid and ethylene oxide react neady quantitatively at 100°C to form tris(2-hydroxyethyl)isocyanurate [839-90-7] (THEIC) (48—52). Substitution of propylene oxide yields the hydroxypropyl analogue (48,49). At elevated temperatures (- 200° C). CA and alkylene oxides react in inert solvent to give A/-hydroxyalkyloxazohdones in approximately 70% yield (53). Alternatively, THEIC can be prepared by reaction of CA and 2-chloroethanol in aqueous caustic (52). THEIC can react further via its hydroxyl fiinctionahty to form esters, ethers, urethanes, phosphites, etc (54). Reaction of CA with epichlorohydrin in alkaline dioxane solution gives... 

Azole iV-oxides, iV-imides and iV-ylides are formally betaines derived from iV-hydroxy-, iV-amino- and iV-alkyl-azolium compounds. Whereas iV-oxides (Section 4.02.3.12.6) are usually stable as such, in most cases theiV-imides (Section 4.02.3.12.5) andiV-ylides (Section 4.02.3.12.3) are found as salts which deprotonate readily only if the exocyclic nitrogen or carbon atom carries strongly electron-withdrawing groups. 

Besides trimerisation, leading to the production of polyisocyanurates, isocyanates can react with each other to form polycarbodi-imides with the simultaneous evolution of carbon dioxide ... 

In the absence of solvents and with suitable catalysts the evolution of carbon dioxide simultaneously with the polycarbodi-imide formation gives rise to a foamed product. These foams are cross-linked because of reactions between carbodi-imide groups and free isocyanate groups. Raw materials for such foams are now available from Bayer (Baymid). 

The reaction of ethylene carbonate with acid imides which yields V-hydroxyethyl derivatives w as applied to 6-azauracil. In agreement with the foregoing findings, 6-azauracil produced a 3-(2-hydroxyethyl) derivative (65) which w as treated with thionyl chloride to convert... 

In the presence of potassium carbonate, alkyl halides reacted with the imidic acid tautomers 154 of l,2,4-triazolo[l,5-c]pyrimidin-2-ones (153) to afford the 2-alkoxy derivatives 155 (85USP4528288 94JMC2371) (Scheme 60). 

A variety of nucleophiles can be employed—e.g. carboxylic acids, phenols, imides, thiols, thioamides, and even /3-ketoesters as carbon nucleophiles. Of major importance however is the esterification as outlined above, and its use for the clean inversion of configuration of a chiral alcohol. 

Problem 7.6 When an unsymmetrjcal alkene such as propene is treated with iV-biomosiiccin-imide in aqueous dimethyl sulfoxide, the major product has the bromine atom bonded to the less highly substituted carbon atom. Is this Markovnikov or non-I Markovnikov orientation Explain. 

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