Cleavage fluoride

Several cortisone derivatives with glucocorticoid effects are most active, if they contain fluorine in the 9or-position together with an Il(9-OH group. Both substituents are introduced by the cleavage of a 9,11 -epoxide with hydrogen fluoride. The regio- and stereoselective formation of the -epoxide is achieved by bromohydrination of a 9,11-double bond and subsequent alkali treatment (J. Fried, 1954). 

Analytical Methods. Fluorite is readily identified by its crystal shape, usually simple cubes or interpenetrating twins, by its prominent octahedral cleavage, its relative softness, and the production of hydrogen fluoride when treated with sulfuric acid, evidenced by etching of glass. The presence of fluorite in ore specimens, or when associated with other fluorine-containing minerals, may be deterrnined by x-ray diffraction. 

The oxidation may be carried out with an inert solvent thermally (35), with a sensitizer such as bromine (36), with uv radiation (37), or over a suitable catalyst (38). Principal by-products of all these oxidation processes are the acyl fluoride products derived from oxidative cleavage of the perfluoroaLkene (eq. 

Bu4N F , THF, "2 min. The TBDS group is less reactive toward tri-ethylammonium fluoride than is the TIPDS group. It is stable to 2 M HCl, aq. dioxane, oyemight. Treatment with 0.2 MNaOH, aq. dioxane leads to cleavage of only the Si—O bond at the 5 -position of the uridine derivative. The TBDS derivative is 25 times more stable than the TIPDS derivative to basic hydrolysis. 

Trimethylsilyl ethers are readily cleaved by fluoride ion, mild acids, and bases. If the TMS derivative is somewhat hindered, it also becomes less susceptible to cleavage. A phenolic TMS ether can be cleaved in the presence of an alkyl TMS ether [Dowex lX8(IfO ), EtOH, rt, 6 h, 78% yield]. ... 

Af HF, 0.1 MNaF, pH 5, THF, 25°, 2 days, 77% yield. In this substrate a mixture of products resulted from attempted cleavage of the t-bu-tyldimethylsilyl ether with tetra- -butylammonium fluoride, the reagent generally used. ... 

These reactions proceed by alkoxide or fluoride attack at silicon which results in C—Si bond cleavage and elimination of the leaving group from the fi carbon. These reactions are stereospecific anti eliminations. 

In contrast to hydrogen-type ethers, a-haloethers, both linear and cyclic, are relatively easily cleaved by anhydrous hydrogen fluoride. Bis( 1,1 -difluoroalkyl) ethers are converted to 1,1,1 -trifluoroalkanes and alkanoyl fluorides The cleavage temperature depends on the substituents present ethers having no electronegative substituents other than a-fluorines are readily cleaved below 20 °C, 3-halo-1,1-di fluoroethers require approximately 70 °C, but 2-halo-1,1-difluoroethers are prac tically resistant toward hydrogen fluoride [/I (equation 1)... 

A nonconventional synthesis of the known inhalation anaesthetic, 2-bromo-2 chloro-l,l,l-trifluoroethane (Halothane), based on the reaction of ethyl 1,2 di bromo-1,2-dicliloroethyl ether with anhydrous hydrogen fluoride and sulfur tetrafluoride, has been patented The reaction presumably involves cleavage of the ether linkage, followed by fluorination of the intermediate bromochloroacetyl halide with sulfur tetrafluoride, ethyl halides are the by-products [2] (equation 2)... 

There is continuous interest in cleavage of epoxides as a general method lor the preparation of fluorohydrins Epoxides are effectively cleaved under mild conditions by a 70% hydrogen fluoride-pyridine complex (Olah s reagent). The... 

Table 1. Cleavage of Glycidic Esters, Glycidic Amides, and Glycidic Nitriles by Hydrogen Fluoride-Pyridine Complex 110,11]...

In contrast to phosphorus esters, sulfur esters are usually cleaved at the carbon-oxygen bond with carbon-fluorine bond formation Cleavage of esteri nf methanesulfonic acid, p-toluenesidfonic acid, and especially trifluoromethane-sulfonic acid (tnflic acid) by fluoride ion is the most widely used method for the conversion of hydroxy compounds to fluoro derivatives Potassium fluoride, triethylamine trihydrofluoride, and tetrabutylammonium fluoride are common sources of the fluoride ion For the cleavage of a variety of alkyl mesylates and tosylates with potassium fluoride, polyethylene glycol 400 is a solvent of choice, the yields are limited by solvolysis of the leaving group by the solvent, but this phenomenon is controlled by bulky substituents, either in the sulfonic acid part or in the alcohol part of the ester [42] (equation 29)... 

A one-pot conversion of benzyl alcohols to benzyl fluorides by treatment of the alcohols with a combination of methanesulfonyl fluoride, cesium fluoride and 18-crown 6 ether in tetrahydrofuran has been repotted The reaction involves mesylation of the alcohols followed by cleavage of the resultant mesyl esters with a fluoride ion The reaction has been extended also to certain heterocycles bearing the N hydroxymethyl group [43] (equation 31)... 

An example of cleavage ol the sulfur-oxygen bond in trifluoromethane-sulfonic ester has been reported Tnfluororaethyl triflate reacts with neutral or anionic nucleophiles with elimination of carbonyl difluoride and formation of trifluoromethanesulfonyl fluoride [57] (equation 32) The mechanism of this reaction involves elimination of fluoride ion, which is a chain carrier in the substitution of fluorine for the trifluoromethoxy group... 

Results of fluorination of lactones with sulfur tetrafluoride depend on the ring size. y-Butyrolactone undergoes ring cleavage to give y-fluorobutyryl fluoride, which IS further fluormated to 1,1,1,4-tetrafluorobutane. The six-membered 1,4-di-... 

Cleavage of 2,2-dibutyl 1,3-dithiolane with fluorine in anhydrous hydrogen fluoride results in the formation of 5,5-difluorononane [7] (equation 3)... 

In addition, there is a cleavage reaction whereby a perfluoroorgamc group is cleaved from a metal by a base, for example, phenyllithium [4], ethylmagnesium bromide [5], or a fluoride ion [6] (equations 3-5)... 

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