Alkenes Tetrabutylammonium fluoride

Epoxides are regio- and stereoselectively transformed into fluorohydrins by silicon tetrafluoride m the presence of a Lewis base, such as diisopropyleth-ylamme and, m certain instances, water or tetrabutylammonium fluoride The reactions proceed under very mild conditions (0 to 20 C in 1,2-diohloroethane or diethyl ether) and are highly chemoselective alkenes, ethers, long-chain internal oxiranes, and carbon-silicon bonds remain intact The stereochemical outcome of the epoxide ring opening with silicon tetrafluoride depends on an additive used, without addition of water or a quaternary ammonium fluoride, as fluorohydrins are formed, whereas m the presence of these additives, only anti opening leading to trans isomers is observed [17, 18] (Table 2)... 

The reaction can be done intramolecularly. N-Benzyl pent-4-ynamide reacted with tetrabutylammonium fluoride to an alkylidene lactam. Similar addition of a tosylamide-alkene, with a palladium catalyst, led to a vinyl Al-tosyl pyrrolidine. Similar cyclization reactions occur with tosylamide-alkynes. ... 

A mixture of potassium hydrogen fluoride, 1 M hydrofluoric acid and (V-iodosuccinimide in the presence of tetrabutylammonium fluoride (TBAF) as a phase-transfer catalyst has been shown to effect iodofluorination of alkenes in good yield.163 Dodec-l-ene (6) has been transformed to 2-fluoro-l-iodododecane (7) in 82% yield. TBAF is essential for the reaction to proceed quickly and to improve the yield. The percentage of the side product 1-iodododecan-2-ol is kept to a minimum (0.2%). Many alkenes have been transformed to the corresponding fluoroiodo derivatives by this method.163... 

Several groups have employed N-halosuccinimdes for the halofluorination of alkenes. Laurent and co-workers have found that triethylamine tris(hydrofluoride) is a suitable fluoride source for the halofluorination of a number of alkenes (Scheme 70).137 Other examples of halofluorinations include NBS and tetrabutylammonium fluoride as the halogen sources for the formal addition of BrF across funtionalized cyclohexenes138 and the halofluorination of alkenes and alkynes by all three N-halosuccinimides and polymer-supported HF.139... 

The direct azido phenylselenenylation of alkenes can be accomplished by four different methods A126 reaction with phenylselenenyl chloride and sodium azide in dimethyl sulfoxide or dimethylformamide B127 reaction with diphenyldiselenide, sodium azide and iodosobenzene diacetate in dichloromethane C128 reaction with iV-phenylselenophthalimide (TV-PSP) and azidotrimethylsilane in dichloromethane D128 as in C but in the presence of 0.1 equivalent of tetrabutylammonium fluoride. 

Readily available 2-chloroalkyl-0,0-diethylthiophosphates 304, prepared from alkenes and diethoxyphosphoranesul-fenyl chloride, reacted, during 3 h at — 78 °C, with tetrabutylammonium fluoride trihydrate in THF to give thiiranes 305 in moderate or good yield <1997HAC429>. A one-pot version of this reaction is known (Scheme 90 Table 16). 

Aryl-1 -fluorocyclopropanes 2 were synthesized by irradiation of a 3-aryl-3-fluoro-3//-diazirine and an alkene (2 > 300 nm, 25 °C) in a screw-top Pyrex Carius tube (Houben-Weyl, Vol. E19b, p980). The starting 3-aryt-3-fluoro-3//-diazirines were prepared from the corresponding 3-aryl-3-bromo-3//-diazirines and anhydrous tetrabutylammonium fluoride. The products were purified by column chromatography on silica gel (purity > 97%). Due to the explosive properties of diazirines, this method is not suitable for large-scale preparations. 

Cyclopropylalkan-l-ones are obtained from l-alkoxy-2-cyclopropyl-l-alkenes and l-acetoxy-2-cyclopropylaIk-l-enes under protic conditions and 2-cyclopropyl-l-trimethyl-siloxyalk-l-enes using tetrabutylammonium fluoride. The yields are usually moderate. 

Moreover, the same 2-fluoro-l-iodoalkanes (see Table 11) can be synthesized in yields of 60-94% by iodofluorinations of the corresponding alkenes using the tetrabutylammonium dihydrogen trifluoride//V-iodosuccinimide reagent in dichloromethane. This reaction is carried out in glassware for analytical details of the 2-fluoro-l-iodoalkanes, see ref 336 (for halofluorina-tions using tetrabutylammonium hydrogen fluoride//V-halosuccinimide in dichloromethane, see ref 337). 

Tetrabutylammonium(triphenylsilyl)difluorosilicate is a new fluoride source soluble in anhydrous, nonhygroscopic and neutral organic solvents. This reagent converts organic halides and sulfonates into fluorides, however, 4-6 equivalents are required. 1-Iodooctane is converted to 1-fluorooctane (33) in 74% yield, the rest (26%) being the alkene.221 Apparently with tetra-alkylammonium fluorides, the formation of alkenes is generally not completely suppressable. 

The formation of 10 is an example of the addition of chloromethyl ethers to perfluorinated alkenes in the presence of potassium fluoride and a catalytic amount of tetrabutylammonium... 

Syntheses of 5,6- and Other Unsaturated Cyclic Compounds - A general approach to enol ethers, illustrated by conversion of nitro-alkene 37 into 38 by treatment with tetrabutylammonium hydrogen sulfate-potassium fluoride, has been described. The reaction was also found to be applicable to a wide range of acyclic sugars (see Section 4 below). 

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