Acyl fluorides pyridines

These reactions are most important for the preparation of acyl fluorides. " Acyl chlorides and anhydrides can be converted to acyl fluorides by treatment with polyhydrogen fluoride-pyridine solution" or with liquid HF at — 10°C. Formyl fluoride, which is a stable compound, was prepared by the latter procedure from the mixed anhydride of formic and acetic acids. Acyl fluorides can also be obtained by reaction of acyl chlorides with KF in acetic acid or with DAST. Carboxylic esters and anhydrides can be converted to acyl halides other than fluorides by the inorganic acid halides mentioned in 10-77, as well as with PhsPXa (X = Cl or but this is seldom done. Halide exchange can be carried out in a... 

Recently, the Rovis group reported acylation of dialkylzinc and diphenylzinc reagents by acyl fluorides, chlorides, anhydrides, and thioesters in the presence of air sensitive Ni(cod)2 or air stable Ni(acac)2 and a bidentate ligand, such as (2-diphenylphosphinoethyl)pyridine (pyphos Scheme 125).325 It is noteworthy that epimerizable stereocenters tolerated the conditions used. 

Pyridine (1) is a weak and good base and good solvent for effecting aminolysis of acyl fluorides (see Section 7.12) and for preparing Boc-amino-acid iV-carboxyanhydrides (see Section 7.14) and activated esters by the carbo-diimide method (see Section 7.7), especially the esters of Boc-amino acids, as it prevents decomposition of the activated residue (see Section 7.15). It is the preferred base for aminolysis of acyl fluorides in dichloromethane. 

Acyl chlorides (or anhydrides) react in 70% hydrogen fluoride/pyridine to give acyl fluorides in high yields31 (for HF/melamine, see ref 248). 

The perfluoroorganozmc compounds have limited application in organic syn thesis because of their lack of reactivity However, heptafluoro 1 methylethylzinc iodide reacts with acyl fluorides or anhydrides of carboxylic acids in the presence of pyridine to give the corresponding ketones [38] (equations 28 and 29) In the presence of zinc fluoride, acyl chlorides can be used as substrates [33]... 

For reactions carried out in homogeneous solution or under solid-phase conditions the use of Fmoc amino acid chlorides is limited by the competition between their aminolysis and the formation of the less reactive oxazol-5(4//)-ones in the presence of tertiary amines, which are essential components of such reaction systems. To improve the results under these conditions a hindered base, e.g. 2,6-di-/er/-butylpyridine, can be used as a hydrogen chloride acceptor since conversion to oxazol-5(4//)-one is slow with such bases. Although shown to be advantageous in certain cases, Fmoc amino acid chlorides are used in homogeneous solution synthesis only in particular cases. They react efficiently in the presence of pyridine with weak nucleophiles such as imine 2P l (Scheme 2) where other activated species such as an active ester, anhydride, acyl fluoride, and acyl imidazolide fail. 

Acylation (see also Acetylation, Cathylation) Acyl fluorides. Benzoylchloride (see Hippuric acid, preparation). N-Carbonylsulfamic acid chloride. Chloroacetic anhydride. Chloroacetyl chloride. Magnesium. Mesyl chloride. Methanesulfonic anhydride. 1-Morpholinocyclo-hexene. Pyridine. Sodium diisopropylamide. Sodium hydride. Trifluoroacetic anhydride. 

Trifluoro-l,3,5-triazine (cyanuric fluoride) is a colorless liquid, which is used mainly in dye manufacturing. Cyanuric fluoride is a mild reagent that is suitable for the preparation of acyl fluorides even when unsaturated double bonds, hydroxyl groups, or aromatic rings are found in the molecule. Carboxylic acids were converted into the corresponding acyl fluorides by treatment with cyanuric fluoride in the presence of pyridine (Equation 56). 

The toxicity of 2,4,6-trifluoro-jy/n-triazine (cyanuric fluoride) has been quantified 2,4,6-tris(trifluoromethyl)-j> /n-triazine is considerably less toxic. A wide range of acyl fluorides may be obtained in high yields by treating the corresponding acids at 20 °C with cyanuric fluoride in acetonitrile in the presence of pyridine double bonds, hydroxy-groups, and aromatic nuclei are unaffected. ... 

The Mspoc protected amino acids can be converted to their respective acyl fluorides by treatment with cyanuric fluoride and pyridine (eq 5). The Mspoc acyl fluorides are obtained in crystalline form, in contrast to the undefined foams or amorphous products that are typically obtained with other protecting groups. 

Potentially tautomeric pyrimidines and purines are /V-alkylated under two-phase conditions, using tetra-n-butylammonium bromide or Aliquat as the catalyst [75-77], Alkylation of, for example, uracil, thiamine, and cytosine yield the 1-mono-and 1,3-dialkylated derivatives [77-81]. Theobromine and other xanthines are alkylated at N1 and/or at N3, but adenine is preferentially alkylated at N9 (70-80%), with smaller amounts of the N3-alkylated derivative (20-25%), under the basic two-phase conditions [76]. These observations should be compared with the preferential alkylation at N3 under neutral conditions. The procedure is of importance in the derivatization of nucleic acids and it has been developed for the /V-alkylation of nucleosides and nucleotides using haloalkanes or trialkyl phosphates in the presence of tetra-n-butylammonium fluoride [80], Under analogous conditions, pyrimidine nucleosides are O-acylated [79]. The catalysed alkylation reactions have been extended to the glycosidation of pyrrolo[2,3-r/]pyrimidines, pyrrolo[3,2-c]pyridines, and pyrazolo[3,4-r/]pyrimidines (e.g. Scheme 5.20) [e.g. 82-88] as a route to potentially biologically active azapurine analogues. 

Acylation of hydroxyl groups. Hydroxyl groups of nucleosides are often not acylated in high yield under standard conditions (acid chloride or anhydride in pyridine). However, the reaction occurs in high yield with an anhydride in THF at 22° when catalyzed by fluoride ion. The same conditions also allow replacement... 

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