Alkenes, fluorinated, reaction with alcohols

Mixtures of anhydrous hydrogen fluoride and tetrahydrofuran are successfully used as fluorinating agents to convert 1,1,2-trifluoro-l-allcen-3-ols, easily prepared from bromotrifluoroethene via lithiation followed by the reaction with aldehydes or ketones, to 1,1,1,2-tetrafluoro-2-alkenes The yields are optimal with a 5 1 ratio of hydrogen fluoride to tetrahydrofuran The fluorination reaction involves a fluonde lon-induced rearrangement (Sf,j2 mechanism) of allylic alcohols [65] (equation 40)... 

The reaction of alcohols, alkyl halides or alkenes with alkenes in the presence of anhydrous hydrogen fluoride should lead to conjugated alkylation of the alkenes with simultaneous introduction of an alkyl group and a fluorine atom to give products 1. 

The Prins reaction (electrophilic a-hydroxyalkylation of alkenes) is practicable with hydrogen fluoride as solvent and offers a possibility for the synthesis of fluorinated alcohols. 

The reaction of perfluoroalkyl iodides with alkenes affords the perfluoro-aikyiated alkyl iodides 931. a.a-Difluoro-functionalized phosphonates are prepared by the addition of the iododifluoromethylphosphonate (932) at room temperature[778], A one-electron transfer-initiated radical mechanism has been proposed for the addition reaction. Addition to alkynes affords 1-perfluoro-alkyl-2-iodoalkenes (933)[779—781 ]. The fluorine-containing oxirane 934 is obtained by the reaction of allyl alcohol[782]. Under a CO atmosphere, the carbocarbonylation of the alkenol 935 and the alkynol 937 takes place with perfluoroalkyl iodides to give the fluorine-containing lactones 936 and 938[783],... 

The reaction of phenyl-substituted alkenes (2-phenylprop-l-ene, ( )-l-phenylprop-l-ene, 1,1-diphenylethene, 1,1-diphenylprop-l-ene) with F-Teda BF4 (6) in the presence of various alcohols results in the formation of vicinal fluoro alkoxy adducts with Markovnikov-type regioselec-tivity.89,94 The stereochemistry of the fluorination-methoxylation addition reaction is slightly syn predominant in the case of (Z)-stilbene, indene, and dibenzosuberenone, while equal amounts of both diastereoisomers are formed in the case of ( )-l-phenylprop-l-ene and acenaphthylene. 

Replacement of fluorine occurs when l,l,l-trifluoro-2,2-dihaloethanes 1 are treated with alkaline alkoxides.59 The products, alkyl 1,1 -difluoro-2,2-dihaloethyl ethers, are probably formed by two separate reactions these are elimination of hydrogen fluoride to give an alkene, followed by addition of the alcohol.59... 

Olah and Li2 have prepared a solid form of this reagent by reaction of anhydrous HF with cross-linked poly-4-vinylpyridine. It is comparable to pyridinium poly (hydrogen fluoride) for hydrofluorination of alkenes and alkynes and fluorination of alcohols, but is easier to handle. Work-up of reactions requires only a simple filtration, and the spent reagent can be regenerated with HF for further use. 

Difluorotnethylatcd alcohols 12 and amides 13 as well as fluorinated alkenes 14 are obtained by reactions of alkenyltrifiuoroborates with l-(chloromethyl)-4-fluoro-l,4-diazoniabicyclo-... 

The reaction of the acetate with secondary amines gives various amines with different alkyl and aryl groups, including amino alcohols. Two amines. 13 and 14, with fluorinated alkyl groups have been applied for enantioselective hydrosilylation of alkenes. with considerable success38 (Sections D.4.3. and D.9.). 

We want to convince you that this chemistry is useful and also that it works in more complicated molecules so we are going to describe in part the preparation of the antibiotic ofloxacin. The sequence starts with an aromatic compound having four fluorine atoms. Three are replaced sequentially by nucleophiles and the last is present in the antibiotic itself. The first reaction is a conjugate substitution of the ethoxy group marked in orange. An amino alcohol is used as the nucleophile and it is the more nucleophilic amino group (rather than the hydroxyl group) that adds to the alkene. 

As a consequence of the above summarized properties of fluorinated alcohols, they are ideal solvents for the generation of cationic or radical-cationic species or reaction intermediates. This eflect has been exploited numerous times, for example, in the investigation of organic radical cations [11]. At the same time, it lies at the heart of the catalysis of alkene epoxidation with hydrogen peroxide and of Baeyer-Villiger-type oxidations of carbonyl compounds. The mechanisms of the latter two reaction types are discussed in more detail in Sections 4.3.1.1 (epoxidation) and Section 4.5.1 (Baeyer-VUliger). 

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