Olefins, alkyl-substituted fluorinated

The Hiyama coupling offers a practical alternative when selectivity and/or availability of other reagents are problematic. Hiyama et al. coupled alkyltrifluorosilane 74 with 2-bromofuran 73 to give the corresponding cross-coupled product 75 in moderate yield in the presence of catalytic Pd(Ph3P)4 and 3 equivalents of TBAF [65]. In this case, more than one equivalent of fluoride ion was needed to form a pentacoordinated silicate. On the other hand, alkyltrifluorosilane 74 was prepared by hydrosilylation of the corresponding terminal olefin with trichlorosilane followed by fluorination with C11F2. This method provides a facile protocol for the synthesis of alkyl-substituted aromatic compounds. 

This route is especially valuable for the transformation of electron-rich heteroaromatic compounds into their fluorinated analogues, which are not suitable for the nucleophilic exchange route. The method has been extended by addition of fluorinated olefins. The fluoroolefins add in a radical process to the 2-position of tetrahydrofuran, followed by perfluori-nation to give the perfluorinated 2-alkyl-substituted tetrahydrofurans in excellent yields [84JFC(25)523 85JFC(29)323] (Scheme 3). 

The reactivities of the substrate and the nucleophilic reagent change vyhen fluorine atoms are introduced into their structures This perturbation becomes more impor tant when the number of atoms of this element increases A striking example is the reactivity of alkyl halides S l and mechanisms operate when few fluorine atoms are incorporated in the aliphatic chain, but perfluoroalkyl halides are usually resistant to these classical processes However, formal substitution at carbon can arise from other mecharasms For example nucleophilic attack at chlorine, bromine, or iodine (halogenophilic reaction, occurring either by a direct electron-pair transfer or by two successive one-electron transfers) gives carbanions These intermediates can then decompose to carbenes or olefins, which react further (see equations 15 and 47) Single-electron transfer (SET) from the nucleophile to the halide can produce intermediate radicals that react by an SrnI process (see equation 57) When these chain mechanisms can occur, they allow reactions that were previously unknown Perfluoroalkylation, which used to be very rare, can now be accomplished by new methods (see for example equations 48-56, 65-70, 79, 107-108, 110, 113-135, 138-141, and 145-146)... 

Halofluorinations take place, as a rule, regioselectively (Markovnikov addition), the olefinic carbons can be substituted with a variety of substituents ranging from alkyl or aryl groups to different electron-withdrawing functions see for example refs 31 and 178-180. Bromo-fluorination of 4-/m-butyl-l-methylcyclohexene with /V-bromosuccinimide in 70% hydrogen fluoride/pyridine gave two stereoisomers 1 and 2.181... 

USE Fluorinating agent. Catalyst in alkylation, acylation, polymerization and condensation reactions in hydrofluori-nation of olefins in production of substituted pyridines. In production of petroleum products. See Thompson, loc, cit. Mugic Acid, a 1 1 HSOaF-SbFs soln, is used in the study of stable sol ns of alkyl - and arylcarbonium ions Olah, Science 168, 1298 (1970). 

Olefins add hydrogen fluoride very readily, but polymerization of the olefins also occurs as a side reaction. Traces of acid and water, or temperatures of about 70°, lead to loss of HF from the alkyl fluorides produced. Preparative importance attaches to addition of HF to chlorinated olefins, whose tendency to polymerize in presence of HF is less the more Cl atoms are attached to the doubly bonded carbon atoms. HF adds readily to olefins with unsymmetrical halogen substitution, such as CH2=CHX, RCH=CX2, or RCX=CH2, but with greater difficulty when halogen is attached to both the doubly bonded carbon atoms. BF3, which assists removal of H+ from HF by complex formation, accelerates the reaction but also the exchange of halogen for fluorine and the resin formation by polymerization that occur as parallel reactions.169... 

Toxicology OSHA PEL/TWA 2.5 mg(F)/m highly toxic corrosive irritant to skin, eyes, and mucous membranes probable poison by inh. causes severe burns TSCA listed Precaution DOT Corrosive reacts violently with water, although incompletely and reversibly hydrolyzed Storage Store under nitrogen refrigerate Uses Catalyst for alkylation, acylation, condensation, polymerization reactions in hydrofluorination of olefins in prod, of substituted pyridines in prod, of petrol, prods. fluorination reagent... 

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