3.3.3- trifluoropropene, reaction

A similar mechanism operates in the reaction of 3,3,3-trifluoropropene with benzene and aluminum chloride [12 13] Perfluorophenylpropene undergoes intramolecular electrophilic attack m a rare example of ring closure at a C -F bond [14] (equation 11)... 

Fluorobenzene is readily alkylated with alkenes in the presence of protic acids, however, the isomenc purity of the product is poor, and polysubstitution can result Thus, propene and sulfuric acid alkylate fluorobenzene at 20 C to yield a 45 55 ortho/para ratio of the inonoalkyl product m addition to di- and triiso propylfluorobenzene [i5] The reaction of benzene and trifluoropropene at 25 °C in HF-BF3 gives a mixture of mono-, bis-, and tns(3,3,3-trifluoropropyl)ben zene [72, 75] (equation 12)... 

The easy homolysis of C-Br bond in CBr4 allowed us to conduct the radical chain reaction of CBr4 with 3,3,3-trifluoropropene under common conditions (benzoyl peroxide), although in this case the strong electrophiles are used as reagents (an addend and a monomer), i.e. a very unfavorable combination of polar factors for proceeding the process takes place (ref. 6). 

Trifluoropropene is a compound of special interest in this series. Some transformations of the intermediate telomer radicals had been observed in this case, which prompted to study this reaction in more details. In addition to telomers C6H5CH2(CH2CHCp3)nBr (T Br, n = 1,2), the authors have found compound PhCH=CHCH(CF3)CH2CH2Cp3 and explained its formation by rearrangement of the intermediate radical with two monomer units followed by easy... 

In subsequent work the same supported catalysts were used in different reactor setups [20] (Figure 3.3). A vapour-phase reactor in which the supported catalyst was mounted on a bed was used for the hydroformylation of volatile alkenes such as cis-2-butene and trifluoropropene. The initial activities and selectivity s were similar to those of the homogeneous solutions, i.e. a TOF of 114 and 90% ee in the hydroformylation of trifluoropropene was reported. No rhodium was detected in the product phase, which means less then 0.8% of the loaded rhodium had leached. The results were, however, very sensitive to the conditions applied and, especially at longer reaction times, the catalyst decomposed. In a second approach the polymer supported complex was packed in a stainless steal column and installed in a continuous flow set-up. 

Recently, 3,3,3-trifluoro-2-propenyl zinc reagent has been prepared by the reaction of 2-bromo-3,3,3-trifluoropropene with Zn(Ag) and TMEDA in THF in good yield [169]. TMEDA is essential to the preparation of this zinc reagent, presumably by formation of a chelate structure which can stabilize the zinc reagent (Scheme 58). 

The reactions of a-unsaturated alkanecarboxylic acids with sulfur tetrafluoride are usually accompanied by polymerization and other side reactions and give poor yields of trifluoroal-kencs. Although acrylic acid is reported to give 3,3,3-trifluoropropene in 45 % yield,41 numerous attempts by the author to repeat this reaction have failed. 

The reaction of 3,3,3-trifluoropropene with a sulfur tetrafluoride/hydrogen fluoride/disul-fur dichloride system proceeds at 20 C to give a mixture of diastereomers of bis[2-fluoro-l-(tri-fluoromethyl)ethyl] sulfide (18) in high yield.243... 

Electrophilic activation of sulfur chlorides could be achieved by conducting the reaction with fluoroolefin in the presence of strong acids. For example, trifluoropropene readily reacts with the mixture S2C12/HF/SF4 to produce the corresponding isopropylsulfide 55 in high yield [143] ... 

More interesting features or reaction leading to telomeric distributions are described below. Concerning hydrosilylation reactions, a wide range of fluoroalkenes have been used and the results have been reported [291, 292] or very well reviewed by Marciniec [303] leading mainly to monoadducts, except for 1,1,1-trifluoropropene,TFE [122-124] and CTFE [122],... 

More recently, this reaction was performed again by Haszeldine [95] with trifluoropropene as the monomer ... 

As we have already mentioned, ruthenium complexes predominantly catalyze the dehydrogenative silylation of alkenes but competitively with the hydrosilylation so the reaction usually gives a mixture of the dehydrogenative silylation and hydrosilylation products. Ru3(CO)12 appears to be a very active catalyst for the dehydrogenative silylation of styrene, para-substituted styrenes [ 19, 20],trifluoropropene and pentafluorostyrene [21] by trialkyl-, phenyldialkyl-silanes (but also triethoxysilane) (Eq. 10). 

The regiochemistry of Diels-Alder reactions with 3.3.3-trifluoropropene (1) shows that the inductive effect of a trifluoromethyl group increases the magnitude of the molecular orbital coefficient of the unsubstituted terminus, but the effect is not great enough to achieve high regioselectivity with dienes other than l-methoxy-3-(trimethylsiloxy)buta-l,3-diene (Danishefsky s diene, 4) compare the reaction of 1 with 2, 3, and 4. ... 

Other substituent groups are usually introduced via Hydrosilation reactions. In this important reaction, Si-H bonds add across C=C or C=C bonds in 1,2 fashion to give products. Many transition metals and their complexes will catalyze hydrosilation, but the usual catalyst is platinum see Hydrosilation Catalysis). Thus CF3CH2CH2Si(Me)Cl2 is made by hydrosilation of 3,3,3-trifluoropropene with methyldichlorosilane (equation 12). n-Alkylmethyldichlorosilanes can be made similarly, by hydrosilation of l-aUcenes. Vinylmethyldichlorosilane may be obtained in analogous fashion by hydrosilation of acetylene, as shown in equation (13). An alternate route to the same compound is hydrosilation of vinyl chloride, followed by dehydrochlorination (equations 14 and 15). 

The orientation of electrophilic addition to trifluoropropene was originally thought to be a reflection of the relative stabilities of the intermediate carbocations 4.15A and 4.15B (Figure 4.15), but it was subsequently found that trifluoropropene is dimerised, rather than protonated in highly acidic media [47, 48]. Deuterium labelling studies indicated that the reaction proceeds via initial fluoride ion abstraction to yield an intermediate allyl cation [49] (Figure 4.16). 

Systems with perfluoroalkyl groups directly attached to the double bond are particularly unreactive towards electrophiles but reaction of hexafluoropropene (HFP) with SbFs leads to a perfluoroallyl cation, which then reacts with another molecule of HFP to give a dimer, probably by an electrophilic process [168] (Figure 7.51) that is analogous to that described earlier for 1,1,1-trifluoropropene [169], (Chapter 4, Section VIB). Similar addition and isomerisation reactions, which proceed via carbocationic intermediates, are given in Figure 7.52 [170-172]. 

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