Fluoride reaction with epoxides

Cesium fluoride reacts with epoxides to form cesium alcoholates that can be transformed into a plethora of ethers and esters in good yield, for example, reaction of 12 to give 13. Methyl-ation with iodomethane is common. For sensitive alcohols silver oxide is the base of choice." No elimination to the a,)S-unsaturated sulfoxides was reported, when alcohols 14 were treated w ith iodomethane in dimethylformamide to give ethers 15." ... 

Perfluoroalkoxyanions are also generated by reaction of fluoride ion with acid fluorides and with epoxides (see Section niB, below). Reaction of the (CF3)2CO—CsF complex with tetrafluoroethene [135] gives alkoxide 8.34A, not a carbanion 8.34B (Figure 8.34). In the presence of iodine, however, ethers are formed [126], indicating the formation of intermediate hypoiodites, RpOI (Figure 8.35). 

The reaction of OF2 and various unsaturated fluorocarbons has been examined (35,36) and it is claimed that OF2 can be used to chain-extend fluoropolyenes, convert functional perfluorovinyl groups to acyl fluorides and/or epoxide groups, and act as a monomer for an addition-type copolymerization with diolefins. 

Preparation. The preparation of tetrafluoroethylene has been described previously. Perfluorovinyl ethers (4—7) are prepared by the following steps. Hexafluoropropylene [116-15-4] (HEP) is oxidized to an epoxide HEPO [428-59-1] (5) which, on reaction with perfluorinated acyl fluorides, gives an alkoxyacyl fluoride. 

General Reaction Chemistry of Sulfonic Acids. Sulfonic acids may be used to produce sulfonic acid esters, which are derived from epoxides, olefins, alkynes, aHenes, and ketenes, as shown in Figure 1 (10). Sulfonic acids may be converted to sulfonamides via reaction with an amine in the presence of phosphoms oxychloride [10025-87-3] POCl (H)- Because sulfonic acids are generally not converted directiy to sulfonamides, the reaction most likely involves a sulfonyl chloride intermediate. Phosphoms pentachlotide [10026-13-8] and phosphoms pentabromide [7789-69-7] can be used to convert sulfonic acids to the corresponding sulfonyl haUdes (12,13). The conversion may also be accompHshed by continuous electrolysis of thiols or disulfides in the presence of aqueous HCl [7647-01-0] (14) or by direct sulfonation with chlorosulfuric acid. Sulfonyl fluorides are typically prepared by direct sulfonation with fluorosulfutic acid [7789-21-17, or by reaction of the sulfonic acid or sulfonate with fluorosulfutic acid. Halogenation of sulfonic acids, which avoids production of a sulfonyl haUde, can be achieved under oxidative halogenation conditions (15). 

Rearrangement of fluorine with concomitant ring opening takes place in fluorinated epoxides Hexafluoroacetone can be prepared easily from perfluo-ropropylene oxide by isomerization with a fluorinated catalyst like alumina pre treated with hydrogen fluoride [26, 27, 28] In ring-opening reactions of epoxides, the distribution of products, ketone versus acyl fluoride, depends on the catalyst [29] (equation 7) When cesium, potassium, or silver fluoride are used as catalysts, dimenc products also are formed [29]... 

Fluorohydrins.1 Both this reagent (1) and Olah s pyridinium poly (hydrogen fluoride) (2) serve as an attenuated source of hydrogen fluoride, and both convert simple epoxides into fluorohydrins, but reactions with 1 require higher temperatures than those with 2. The two reagents can differ in the regioselectivity, with steric factors being more important in reactions of 1 than those of 2. 

Epoxidation of ot.fl-unsaturated ketones by hydrogen peroxide or /-butyl peroxide is promoted by the addition of tetra-n-butylammonium fluoride [10], whereas the corresponding reaction with 1,4-disubstituted but-2-en-l,4-diones is catalysed by quaternary ammonium iodides [11], Oxiranes are also produced by the catalysed reaction of /-butyl peroxide with a,f)-unsaturated sulphonates under basic conditions [12]. 

Conversion of the resulting separate D-seco D-E trans i-vincadiffor-mine diols 198-201 to their primary tosylates and tertiary trimethylsilyl-oxy derivatives 202-205 and coupling to vindoline by the chlorination-silver tetrafluoroborate-potassium borohydride sequence provided amino tosylates 206-209, which could be directly subjected to cyclization or, alternatively, converted to the C-20 -C-21 epoxides 178, 181, 210, and 211 by reaction with tetrabutylammonium fluoride (Scheme 53). While cyclization of the tosylates 206-209 led essentially only to quaternary salts which could be debenzylated to provide the lower energy atropi-somer of vinblastine (1), leurosidine (56), vincovaline (184), and its C-20 epimer (212) respectively, cyclization of the epoxides 178, 181, 210, and... 

A series of functionalized alkenes has been subjected to selective epoxidation reactions. Oxidation of perfluorinated vinyl polyethers by bubbling oxygen through the liquid that contains a catalytic amount of a Lewis acid, e.g. antimony(V) fluoride, results in the formation of acid fluorides together with a smaller amount of C = C bond cleavage.76 Perfluorinated pentaaIkyI-2.3-dihydrofuran 38, an example of an unsaturated cyclic ether that is quite stable owing to perfluoroalkylation. is epoxidized by hypochlorite to the product 39 at 45 C.62... 

Again, difluorohalomethyl,50,58 aminodifluoromethyl59 or difluoro(sulfonyloxy)methyl derivatives (e.g., 8)58,60-63 Can be aminolyzed in a similar manner to yield amidines59,63 or amides.50 58,60-62 In the latter process the intermediacy of acid fluorides (see Section 6.1.2.) has been proposed. By analogy, reaction of monoalkylated perfluorinated epoxides with amines leads to a-functionalizcd amides.64 65 In the presence of fluoride ions, perfluorinated epoxides can rearrange to acid fluorides which can be further elaborated with amines to provide the respective amides.63... 

FluorohydrinsThese have usually been obtained by reaction of epoxides with hydrogen fluoride at high temperatures. This reaction can be carried at 0° with SiF4 in combination with a base such as diisopropylethylamine or even Bu4NF. In all cases, the fluorine atom is introduced at the more substituted carbon. Highest... 

Lithiation of compound 560 with s-BuLi-TMEDA in THF at —78 °C following an inverse addition protocol provided the anion 561. It reacts with primary alkyl iodides and triflates, silyl chlorides, diphenyl disulfide, epoxides, aldehydes, ketones, imines, acyl chlorides, isocyanates and sulfonyl fluorides to yield the expected compounds 562 (Scheme 152). The transmetallation of compound 561 with ZnBr2 allowed the palladium-catalyzed cross-coupling reaction with aryl and vinyl bromides837. When the reaction was quenched with 1,2-dibromotetrafluoroethane, the corresponding bromide 562 (X = Br) is obtained838. 

Anhydrous hydrogen fluoride itself is not recommended for ring-opening fluorinations of simple epoxides as it causes polymerization, rearrangement and other side reactions. With simple epoxides, low to moderate yields of fluorohydrins can be obtained when anhydrous hydrogen fluoride is diluted with organic solvents. 

In combination with aluminum Irifluoride, an increase in reactivity of potassium and sodium hydrogen fluoride towards epoxides is observed. " The reaction can be further accelerated by ultrasonic irradiation. From the product distribution it can be assumed that the mechanism of the ring opening under these conditions is dilTercnt from the reaction with potassium hydrogen fluoride alone. Probably a reaction between the hydrogen difluoride salt and aluminum trifluoride takes place with liberation of hydrogen fluoride in situ. This method is, therefore, more related to those discussed in Section 1.1.4.3.2.1.1. 

Some reactions of epoxides with fluoride and perfluoroalkoxide ions were referred to in Section IB, Subsection 2 (above), and the importance of polymers of these systems was stressed. There are numerous publications or patents concerning the S3mthesis of these... 

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