Acyl tosylates anhydrides

As shown, an asymmetric carboxylic-sulfonic acid anhydride is formed, but the cellulose attack occurs on the C = O group, since a nucleophilic attack on sulfur is slow, and the tosylate moiety is a much better leaving group than the carboxylate group [193]. Similar to other acylation reactions, there is a large preference for tosylation at the 5 position, and cellulose tosylates... 

Attempts to synthesize C-terminal peptide aldehydes using other reductive techniques are less successful. 24"29 The reduction of a-amino acid esters with sodium amalgam and lithium aluminum hydride reduction of tosylated a-aminoacyldimethylpyrazoles resulted in poor yields. 26,29 The Rosemond reduction of TV-phthaloyl amino acid chlorides is inconvenient because the aldehyde is sensitive to hydrazine hydrate that is used to remove the phthaloyl group. 27 28 jV -Z-Protected a-aminoacylimidazoles, which are reduced to the corresponding aldehydes using lithium aluminum hydride, are extremely moisture sensitive and readily decomposed. 25 The catalytic reduction of mixed carbonic/carboxylic acid anhydrides, prepared from acylated a-amino acids, leads to poor reproducibility and low yields. 24 The major problems associated with these techniques are overreduction, racemization, and poor yields. 

Scheme 6 describes the most important reactions of the perimidinespirocyclo-hexadienone 1. A treatment of 1 (R = H) in dimethylsulfoxide (DMSO) solution with methyl iodide in the presence of potassium carbonate affords the A-m ethyl derivative la (R = Me), whereas use of an excessive amount of methyl iodide in this reaction leads to the A,A -dimethyl derivative of the ring-closed tautomer.4,7 By contrast, acylation of la by acetic anhydride or its tosylation by treatment with p-toluenesulfonyl chloride results in the formation of the respective derivatives of the ring-opened tautomeric form lb. 

The present methods for the preparation of N acyl a arylenamides include (i) reductive acylation of ketoximes with iron metal [2] or phosphines [3] in the presence of acyl chlorides or acyl anhydrides (Method A) (ii) metal catalyzed coupling of vinyl halides [4], triflates [5], or tosylates [6] with amides (Method B) (iii) reaction of imine intermediates derived from nitriles with acyl chlorides or anhydrides (Method C) [7] and(iv) Pd catalyzed coupling ofaryl tosylates with N acyl vinylamines (MethodD) [8]. 

Another approach to cephalotaxine intermediate 43 was reported by Weinstein and Craig (65) in 1976 (Scheme 33). The reaction of 3,4-(methy-lenedioxy)-iS-phenethyl tosylate (191), a derivative of the previously used nosylate 117, and sodium 2-carboethoxypyrrole (192), followed by hydrolysis, produced the carboxylic add 193. Intramolecular Friedel-Crafts acylation of 193 with stannic chloride and trifluoroacetic anhydride yielded the benzazepine 194, which was reduced, hydrogenated, and finally oxidized to produce the tricyclic Dolby-Weinreb enamine 43. 

The replacement of acid chlorides or anhydrides for the aldehyde component offers a route to oxazoles (28) with a tosyl substituent in the 4-position. The reaction is presumed81 to occur via the acyl derivatives (27), which, however, have not been isolated. But, nevertheless, the... 

The most prominent cellulose ester produced on the industrial scale is cellulose acetate. The reaction is usually performed with acetic anhydride and with sulfuric acid as a catalyst. To minimize heterogeneities, acetylation is allowed to run nearly to completion, and subsequently partial ester hydrolysis is initiated by the addition of water until a desirable solubility is achieved that corresponds to a DS of about 2.5. Such higher acyl homologues as propanoyl or butanoyl exhibit more thermoplastic properties. Many specialized esters such as chiral (-)-menthyloxyacetates, furan-2-carboxylates, or crown-ether-containing acylates have been prepared on the laboratory scale and characterized by NMR spectroscopy. Various procedures have been applied, using anhydrides and acyl chlorides as acylating agents in combination with such bases as pyridine, 4-dimethylaminopyridine (DMAP), or iV,iV -carbonyldi-imidazole. The substitution pattern of cellulose acetates has also been modified by postchemical enzymatic deacetylation. Cellulose 6-tosylates have been used as activated intermediates for nucleophihc substitution to afford 6-amino-6-deoxy, 6-deoxy, or 6-deoxy-6-halo-celluloses. ... 

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