Tnfluoromethyl group

Methyl group releases electrons stabilizes carbocation than than Tnfluoromethyl group withdraws electrons destabilizes carbocaUon... 

Furan-2-carboxylic acid reacts with sulfur tetrafluoride at 0 °C to give 2-furoyl fluoride, but attempts at further fluorination results in resin formation [222] A second carboxylic group and/or electron withdrawing substiments, such as the nitro or tnfluoromethyl group, stabilize the furan ring Thus, turandicar-... 

Electrochemical reduction of carbon-fliionne bonds occurs at high pH when a carbonyl group is adjacent Polaiographic reduction of a a,a-tnfluoroacetophe-none without loss of fluonne predominates in acidic media to give the alcohol and the corresponding pinacol, whereas reduction of the unprotonated ketone results in hydrogenolysis of the tnfluoromethyl group to form acetophenone as product Il] (equation 8)... 

The electron-withdrawing power of the tnfluoromethyl group in the 2,2,2-tri-fluoroethyl ether of 9-hydroxy-9-(dinitromethyl)fluorene considerably retards its hydrolysis compared with simple alkyl ethers [59] (equation 57)... 

On the contrary, tnfluoromethyl groups severely impede Sj l or reactions when located a to the reaction site. However, aminolysis of l-phenyl-2,2,2,-tri-fluoroethyl tosylate [Sd] and tnfluoroethyl chloride [ST] and its corresponding nonaflate [SS] can be performed under severe conditions (equation 76). 

A bnef paper by Kobayashi indicated some of the potential of this cycli7ation for making fluonne compounds [56] (equation 57) Watanabe et al provided examples of incorporation of a tnfluoromethyl group into a five-membered ring [57] (equation 58) Nevertheless, the full potential of this methodology m preparing fluorine-containing materials has not been realized... 

A peculiar dehydrofluorination occurs when tnfluoromethyl dihydropyndine derivatives are treated with organic bases A double-bond shift and a hydrogen migration convert one tnfluoromethyl group to a difluoromethyl group and aromatize the ring [22] (equation 20)... 

In most cases, fluonnated substituents, when not directly placed at the reaction center, do not influence much the rearrangement routes [7] Favorskn rearrange ment of a substrate bearing a tnfluoromethyl group proceeds as expected [46] (equation 10)... 

An adjacent tnfluoromethyl group sharply increases the electrophilic character of the carbonyl carbon Compounds that readily form hydrates and hemiacetals show a time-dependent reversible mhibition of the en yme acetylcholinesterase (equation 2), in which the tight complex makes inhibition only partially reversible [75] In comparison with a nonfluormated analogue, several aliphatic ketones flanked by CFj and CF2 groups, are exceptionally potent reversible inhibitors of acetylcholinesterase, as documented by companson of inhibition constants shown in equation 3 [16 ... 

Treatment of a- or 0 hydroxyactds with sulfur tetrafluoride leads to conver sion of the carboxylic group into the tnfluoromethyl group, but the hydroxyl group undergoes either fluormation, fluorosulfination, esterification, or dehydration to form esters, ethers, or alkenes The ratio of the products depends on 3 substitution [209, 210] (equations 103 and 104)... 

Treatment of 2,5 and 2,4-furandicarboxylic acids with sulfur tetrafluonde in an excess of hydrogen fluoride leads simultaneously to conversion of the carboxylic groups into tnfluoromethyl groups and addition of two fluorine atoms to the furan ring to give highly fluorinated diastereoisomers of 2,5-dihydrofuran [225,226,227] (equations 117 and 118)... 

Besides sulfur tetrafluonde, only a very few reagents can convert a carboxylic group into a tnfluoromethyl group... 

Fluonnatedphenols are usually oxidized to cyclohexadienone and benzoqui-none derivatives and to products of ring rearrangement and ring degradation Phenols with a tnfluoromethyl group at the nng are hydroxylated by potassium persulfate [57], whereas chloric acid causes oxidation to quinone, mg contraction, and incorporation of chlorine in the product [58] (equation 53)... 

Fluoroalkylamines react with nitrous acid to produce the corresponding unstable fluoroahphatic diazomum ions Placement of the tnfluoromethyl group at a carbon position a, (i, or y to a diazomum ion was used to probe the inductive effect on the chemistry of the transient carbocation resulting from dediazomation [7] If the fluoroalkyl group is bound to the same carbon as the amino group, conversion to the more stable diazo compound occurs For example, 4-diazo-l,l,l,2,2-pentafluoro-3-pentafluoroethyl-3-tnfluoromethylbutane is obtained from the reaction of the poly-fluoroalkylamine salt with sodium nitrite [8, 9] (equation 8)... 

Alkyl fluorides are more reactive than other alkyl halides under Fnedel-Crafts conditions, whereas tnfluoromethyl groups are less reactive than other trihalomethyl groups Thus, a bromoindane is prepared from 1-bromo-l-fluoro-2,2,3,3-letramethylcyclopropane and benzene [S] (equation 8) whereas 3-tnfluo romethylphenyldiphenylchloromethane is obtained from 3-trifluoromethyl-benzotrichlonde and benzene [9] (equation 9)... 

Vinyl and phenyl, tnfluoromethyl groups are reactive in the presence of aluminum chloride [10] Replacement of fluorine by chlorine often occurs Polyfluori-nated trifluoromethylbenzenes form reactive a,a-difluorobenzyl cations in antimony pentafluoride [77] 1 Phenylperfluoropropene cyclizes in aluminum chloride to afford 1,1,3-tnchloro 2 fluoroindene [10] (equation 10) The reaction is hypothesized to proceed via an allylic carbocation, whose fluoride atoms undergo halogen exchange... 

Tnfluoromethyl groups are very resistant to hydrolysis, unless they are allylic or benzylic, or vicinal to a carbon linked to hydrogen. In the last case, elimination of hydrogen fluoride leads to the formation of a difluoromethylene group which is key to additional reactions... 

The photochemical introduction of a tnfluoromethyl group into aromatic and heteroaromatic rings, such as uracil, can be performed also with tnfluoromethyl bromide [75/] (equation 131)... 

Fluorinated organosilanes are also formed by the addition of trimethylsily-lated ketene acetals to hexafluoroacetone [88], a process that appears to be dnven by the enhanced electrophihcity of the carbonyl carbon, which results from the presence of two adjacent tnfluoromethyl groups (equation 72)... 

Cheaper sources of tnfluoromethyl groups have been the goal of several groups The use of sodium trifluoroacetate and copper (I) iodide in dipolar aprotic solvents gave regiospecific trifluoromethylation of aromatic halides [202] (equation 136)... 

Similarly, 6-mercaptopurine in alkaline medium adds across the triple bond in 3,3,3-trifluoropropyne to form the carbon-sulfur bond to the carbon more remote from the tnfluoromethyl group In trifluoromethyl-ferf-butyldiacetylene, the bond is formed to the carbon adjacent to the tnfluoromethyl group [J] (equation 6)... 

Binucleophiles give regiospecific addition to trifluoromethylacetylene with and without subsequent cyclization. Initial attack by the softer nucleophile occurs preferentially at the carbon p to the tnfluoromethyl group [6] (equation 7). 

Alkynes substituted with one or two tnfluoromethyl groups are also highly reactive dienophiles [9] Indeed, hexafluoro-2-butyne is used increasingly as a definitive acetylenic dienophile in difficult Diels-Alder reactions. It was used, for example, to prepare novel inside-outside bicycloalkanes via its reaction with c ,tra/w-l,3-undecadiene [74] (equation 67) and to do a tandem Diels-Alder reaction with a l,l-bis(pyrrole)methane [75] (equation 68) Indeed, its reactions with pyrrole derivatives and furan have been used in the syntheses of 3,4-bis(tn-fluoromethyl)pytrole [76, 77] (equation 69) and l,4-bis(tnfluoromethyl)benzene-2,3-oxide [78] (equation 70), respectively. 

Although one tnfluoromethyl group activates an alkene as a dienophile, two or more can actually inhibit dienophilic reactivity, as evidenced by the fact that... 

Typical HFP contents are about 8.5 mol %. Crystallinity as polymerized is about 70% and drops to about 50% when molded. The stenc requirements of its pendant tnfluoromethyl groups greatly reduce its tendency to crystallize relative to PTFE. The incorporation of HFP also decreases its molecular weight to only about 0.01... 

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