Reactive fluoride anion, preparation

More powerful nitrite scavengers than phthaloyl chloride can improve the yield of the fluoroaro-matic compound. In this regard, phthaloyl fluoride (2) or tetrafluorophthaloyl fluoride, which are easy to prepare from inexpensive sources, are very reactive nitrite anion trapping agents, even for more activated aromatic substrates, suppressing the side reactions initiated by the nitrite ion. " ... 

In a milder variant, fluoride anions are used as mineralizers [23], A typical synthesis system then consists of reactive silica, the SDA, water and NH4F or HF as fluoride source. The pH can be adjusted to neutral or to slightly acidic. It is presumed that the silica is mobilized as fluoride or oxofluoride complexes. Fluoride-mediated syntheses usually yield compounds of high crystallinity, but the crystallization times are longer than for alkaline preparations. 

Alkenyl and arylfluorides (F—C=C) are reactive and so one can imagine that the moiety of (F—C=X) (X=0, NR) should also be reactive. Acyl fluorides have greater stability than the corresponding chlorides toward neutral oxygen nucleophiles such as water and methanol, but appear to be equal reactivity toward anionic nucleophiles and amines [ 1 ]. Cyanuric fluoride 2 is a mild reagent for the preparation of acyl fluorides [2]. The protected amino acids can be transformed into the corresponding amino alcohols without racemization by the reduction of acyl fluorides 3 [3]. 

In media such as water and alcohols fluoride ion is strongly solvated by hydro gen bonding and is neither very basic nor very nucleophilic On the other hand the poorly solvated or naked fluoride 10ns that are present when potassium fluoride dis solves m benzene m the presence of a crown ether are better able to express their anionic reactivity Thus alkyl halides react with potassium fluoride m benzene containing 18 crown 6 thereby providing a method for the preparation of otherwise difficultly acces sible alkyl fluorides... 

Thus removal of water from classical rather inactive fluoride reagents such as tetrabutylammonium fluoride di- or trihydrate by silylation, e.g. in THF, is a prerequisite to the generation of such reactive benzyl, allyl, or trimethylsilyl anions. The complete or partial dehydration of tetrabutylammonium fluoride di- or trihydrate is especially simple in silylation-amination, silylation-cyanation, or analogous reactions in the presence of HMDS 2 or trimethylsilyl cyanide 18, which effect the simultaneous dehydration and activation of the employed hydrated fluoride reagent (cf, also, discussion of the dehydration of such fluoride salts in Section 13.1). For discussion and preparative applications of these and other anhydrous fluoride reagents, for example tetrabutylammonium triphenyldifluorosilicate or Zn(Bp4)2, see Section 12.4. Finally, the volatile trimethylsilyl fluoride 71 (b.p. 17 °C) will react with nucleophiles such as aqueous alkali to give trimethylsilanol 4, HMDSO 7, and alkali fluoride or with alkaline methanol to afford methoxytri-methylsilane 13 a and alkali fluoride. 

Especially for large-scale work, esters may be more safely and efficiently prepared by reaction of carboxylate salts with alkyl halides or tosylates. Carboxylate anions are not very reactive nucleophiles so the best results are obtained in polar aprotic solvents45 or with crown ether catalysts.46 The reactivity order for carboxylate salts is Na+ < K+ < Rb+ < Cs+. Cesium carboxylates are especially useful in polar aprotic solvents. The enhanced reactivity of the cesium salts is due to both high solubility and minimal ion pairing with the anion 47 Acetone is a good solvent for reaction of carboxylate anions with alkyl iodides48 Cesium fluoride in DMF is another useful... 

Germanes hydride, 2 76 reactivity of, 2 87 Germanium anionic cluster, 24 227 azides, preparation, 9 138 properties, 9 135-136, 139, 141 binary carbide not reported, 11 211 carbides, preparation of, 11 163 chalcogenide halides, 23 390 chlorides, mass spectra of, 18 248, 249 complexes, xenon fluoride reactions, 46 85 compounds, see also Organogermanium compounds... 

Carbanion equivalents with anion stabihzing groups are prepared by desilylation of the corresponding materials with cesium fluoride [9-15]. In Scheme 2.6 treatment of aryltrimethylsilanes with cesium fluoride affords carbanion equivalents which add to the carbonyl compounds. The reactive species are not simple organocesium compounds but react as nucleophilic carbanion equivalents. 

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