Anhydrides, open-chain

Anhydrides (open-chain) Anhydrides Cyclic (5-ring)... 

Open-chain carbon skeletons (including cyclic acetals, lactones, lactams, cyclic anhydrides, etc.)... 

The general pattern of alkylation of 2-acylaininothiazoles parallels that of 2-aminothia2ole itself (see Section III.l). In neutral medium attack occurs on the ring nitrogen, and in alkaline medium a mixture of N-ring and N-amino alkylation takes place (40, 43, 161. 163). In acidic medium unusual behavior has been reported (477) 2-acetamido-4-substituted thiazoles react with acetic anhydride in the presence of sulfuric acid to yield 2-acetylimino-3-acetyl-4-phenyl-4-thiazolines (255) when R = Ph. but when R4 = Me or H no acetylation occurs (Scheme 151). The explanation rests perhaps in an acid-catalyzed heterocyclization with an acetylation on the open-chain compound (253), this compound being stabilized... 

However, these authentic cyclic compounds are converted by acetic anhydride or methyl iodide into derivatives of the hypothetical amino-aldehyde form. Methylation gives first the cyclic methiodides (23a-b) and (24) which occur by the addition of a single molecule of methyl iodide in the presence of sodium hydroxide and excess methyl iodide these are converted into the open-chain quaternary methiodides (25a-b) and (26). Similar examples have been given by Garden and by Gensler and co-workers. ... 

Open-chain ligands were the first evaluated for complexation studies with indium and yttrium. The use of diethylenetriaminepentaacetic acid (DTPA) anhydride permitted early evaluation of labeled chelate-conjugates (Figure 2).80 The use of this activated chelating agent was quite popular, until the drawbacks associated with its crosslinking of proteins became apparent. 

Examples of this behaviour are shown in Table 7 where k+ is related to reaction of substrate fully bound to a CTAX micelle and k to reaction in an anionic micelle of SDS. The ratio k+/k is consistently larger than unity for hydrolyses of open chain anhydrides, diaryl carbonates and aryl chloroformates. In addition hydrolysis of 4-nitrophenyl chloroformate is slightly faster in cationic micelles than in water. Spontaneous hydrolyses of N-acyl triazoles are also inhibited less by cationic micelles of CTABr than anionic micelles of SDS (Fadnavis and Engberts, 1982). 

The essential role of our concept of ligand in the proper functioning of the Sequence Rule becomes apparent on examining an example taken from the paper by Cahn et al. (4). The authors state that C(3) of their anhydride 25 (15) is symmetric, as in the free acid, and hence receives no label. Both molecules lack symmetry beyond the trivial and ubiquitous one of C,. The center of C(3) of the anhydride is symmetric only in the sense that it is not linked to four different ligands and therefore is not an asymmetric carbon atom as defined by van t Hoff. However, this observation can be made only if the ring ligands are viewed as open-chain structures, as we are defining them, because only these... 

Addition of a catalyst containing sulfuric acid and acetic anhydride to 3, 5 -di-0-acetylthymidine in acetonitrile results in an equilibrium mixture of a- and ]3-anomers that, after time, gave a substantial quantity of a diastereoisomeric mixture of fully acetylated open-chain nucleosides. These were of type 1.5 with 2 -deoxy and 4 -acetoxy substituents (93TL6779). Open-chain nucleoside was also obtained as well as the expected nucleoside when 5-nitrouracil was condensed with methyl-2,3-dideoxy-3-fluoro-5-0-(4-phenylbenzoyl)-]3-D-cryr/zro-pentofuranoside (94S516). 

Contrary to the stable azepines and diazepines, benzo[ 7]benzofuro[2,3-/][l,4]-oxazepine 272 undergoes ring cleavage under reductive conditions in the acetic acid/acetic anhydride to afford open chain acetoxy amine 273 (Scheme 58, Section 3.2.2 (2001JHC383)). 

In the case of the oximes of the aldose sugars, the situation is more complicated because of the possibility of both open-chain and cyclic structures. That aldose oximes can react in the open-chain form follows from the formation of the nitriles and from the isolation of acylated open-chain aldose oximes as secondary products in preparation of nitriles. For example, Wolfrom and Thompson, by the action of sodium acetate-acetic anhydride on n-glucose oxime, not only obtained pentaacetyl-D-glucononitrile, in 40% yield, but also isolated a small amount of hexaacetyl-oWeAydo-D-glucose oxime (V) identical with that prepared by mild acetylation of pentaacetyl-aWe%do-D-glucose oxime (IV) whose structure was assured by its formation from pentaacetyl-aldehydo-D-glucoae (III). 

This hexaacetyl-aWe%do-D-glucose oxime was easily transformed into the nitrile by heating at 135-140 , or by treatment with sodium acetate-acetic anhydride, and Wolfrom and Thompson considered the open-chain oxime and its acetylated derivative to be an intermediate in the production of the nitrile. We have no proof of the original structure of the oxime. Under the conditions of temperature employed, even a syn oxime can be transformed into the nitrile. If we accept the assumption that the isolated open-chain oxime is the only intermediate, its... 

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. 

Several other dienones were observed to be incapable of effective ring closure to 2//-pyran valence tautomers of 459.164,175,387 In other cases cyclic forms such as 460 and 463 were too unstable to be detected,30,164,388 but their existence, although in negligible concentrations, was proved on the basis of the structure of mutually isomerizing different open-chain forms28,99,388 391 or as adducts with tetracyanoethene30 and maleic anhydride.237,392 The com-... 

In the fused compounds (241) and (242) the furan ring fails to react as a diene and Diels-Alder reaction with dienophiles occurs on the terminal carbocyclic rings. However, (243) and (244) afford monoadducts with dimethyl fumarate by addition to the furan rings (70JA972). The rates of reaction (Table 2) of a number of dehydroannuleno[c]furans with maleic anhydride, which yield fully conjugated dehydroannulenes of the exo type (247), have been correlated with the aromaticity or antiaromaticity of the products (76JA6052). It was assumed that the transition state for the reactions resembled products to some extent, and the relative rates therefore are a measure of the resonance energy of the products. The reaction of the open-chain compound (250), which yields the adduct (251), was taken as a model. Hence the dehydro[4 + 2]annulenes from (246) and (249) are stabilized compared to (251), and the dehydro[4 ]annulenes from (245) and (248) are destabilized (Scheme 84). 

Alder s endo rule applies not only to cyclic dienes like cyclopentadiene and to disubstituted dienophiles like maleic anhydride, but also to open chain dienes and to mo no-substituted dienophiles diphenylbutadiene and acrylic acid, for example, react by way of an endo transition structure 2.113 to give largely (9 1) the adduct 2,114 with all the substituents on the cyclohexene ring cis, and equilibration again leads to the minor isomer 2.115 with the carboxyl group trans to the two phenyl groups. 

The typical features of an open chain anhydride are shown in the spectrum of acetic anhydride (Fig. 3.34). It is also worth noting in this spectrum the very weak C—H stretching band for the methyl group, and the much enhanced intensity of the symmetric C—H bending mode when attached to a carbonyl group. 

It is not necessary to have an all-carbon ring to preserve the cis geometry of a double bond. Lactones (cyclic esters) and cyclic anhydrides are useful too. A double bond in a five- or six-member ed compound must have a cis configuration and compounds like these are readily made. Dehydration of this hydroxylactone can give only a cis double bond and ring-opening with a nucleophile (alcohol, hydroxide, amine) gives an open-chain compound also with a cis double bond. The next section starts with an anhydride example. 

Alkyl-2-(fV-cyanoimino)thiazolidine 1-oxides 684 undergo a ring-enlargement process in the presence of trifluoro-acetic anhydride to afford 5,6-dihydro-2//-l-thia-2,4-diazin-3(4//)-ones 685 (Scheme 297). Initial reaction of 684 with the anhydride leads to open-chain imidate 686, intramolecular displacement of trifluoroacetate gives 4//-l-thia-2,4-diazine 687, which finally hydrolyzes to the isolated product 685 (Scheme 297) <1997SL316, CHEC-III(9.05.10)334>. 

The iV-acylated derivatives of maleic hydrazide, prepared from open-chain compounds, have been found to differ from acylated products obtained from maleic hydrazide acylations. Acylation of 4- or 5-substituted maleic hydrazides should permit the existence of two 0-acylated isomers. So far, only one isomer of unknown structure has been isolated from benzoylation of the 4-methyl analog. Maleic hydrazide and its 2-substituted analogs are 0-acylated with acetic anhydride, acyl halides, and 0,0-dialkylphosphorochlor-... 

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