Trifluoromethyl group direct trifluoromethylation

In the chapter, we established that electron-withdrawing groups direct meta. Among such reactions is the nitration of trifluoromethyl benzene. Draw out the detailed mechanism for this reaction and also for a reaction that does not happen—the nitration of the same compound in the para position. Draw all the delocalized structures of the intermediates and convince yourself that the intermediate for para substitution is destabilized by the CF3 group while that for meta substitution is not. 

As shown in Scheme 29, aromatic and vinylic dithioester groups can be converted to trifluoromethyl groups directly by treating them with (Bu4N)H2p3-DBH (l,3-dibromo-5,5-dimethylhydantoin) (Path a) [17]. The use of NBS or NCS (Path b) in place of DBH yields a,a-difluoro sulfides 130 [17]. This fluorination can also be performed with poly(hydrogen fluoride) pyridinium (Path c) [32]. 

Without any experimental data available for comparison, Shao et al. also proposed and investigated sulfones with different functionalities as solvents [61]. By, e.g., replacing the ether functionality of MEMS with a carbonate, ester, or cyano terminated alkane chain, they in all cases predicted an approximate 0.5 eV increase in (MP2, TD cycle). Other substitutions produced similar effects a trifluoromethyl group for the terminal methyl group (MEMS or EMES), but if also a fluoro atom was introduced in place of the alkane group directly bonded to the sulphur, this second substitution introduced a further 0.5 eV or 1.0 eV stabilization of the solvents with an ester or cyano functionality, respectively. In addition to the TD cycle, adiabatic gas phase IP computations predicted EMS to be the most stable of the linear solvents and supported the stabilizing effects upon functionalization qualitatively [61],... 

Although the trifluoromethyl group is often considered chemically inert, it is known to undergo a variety of reactions and it depends on its position in a molecule. A trifluoromethyl group directly bonded to an aromatic system undergoes hydrolysis in a strong acidic medium ... 

Methods for the synthesis of trifluoromethyl-substituted furans and benzofurans can be divided into several groups direct trifluoromethylation of heterocycle, transformation of functional groups of hetarene into trifluoromethyl substituent, Diels-Alder/retro-Diels-Alder sequence, and various methods for the furan ring formation from precursors bearing trifluoromethyl moiety. 

Ferroelectric liquid crystals containing a chiral unit fluorine, especially those that coruiect a trifluoromethyl group directly to the asymmetric carbon, show a large spontaneous polarization [25-28]. 

Our analysis of substituent effects has so far centered on two groups methyl and triflu oromethyl We have seen that a methyl substituent is activating and ortho para directing A trifluoromethyl group is strongly deactivating and meta directing What about other substituents ... 

As Table 12 2 indicates a variety of substituent types are meta directing and strongly deactivating We have already discussed one of these the trifluoromethyl group Several of the others have a carbonyl group attached directly to the aromatic ring... 

The reaction ot tormamides with sulfur tetrafluoride in the presence of potassium fluoride leads to replacement of both carbonyl oxygen and hydrogen with fluorine. The formyl group is directly converted into the trifluoromethyl group A-(trifluoromethyl)amines are formed in near quantitative yields [233] (equation 121)... 

A trifluoromethyl moiety is a strong electron-withdrawing group which dominates the direction of indolization in the Nenitzescu process. ... 

The directing influence of the trifluoromethyl group also competes with that of the strongly electron-donating methoxyl group. Thus 2-methoxy-5-trifluoromethyl-l,4-benzoquinone (26) was treated with ethyl 3-aminocrotonate (5) to furnish 25% of each of the two possible isomeric indoles 27 and 28. °... 

When electron-withdrawing groups are introduced at the vinyl moiety, ary-lethenes may behave as dienophiles. Thus a-trifluoromethyl styrene (111) interacted with Danishefsky s diene (12b) under thermal or high pressure conditions [37] to regioselectively afford a 1 1 mixture of cycloadducts which were then converted to 4-phenyl-4-trifluoromethyl-2-cyclohexen-l-one (112) (Equation 5.12). A direct access to angularly trifluoromethyl-substituted tricyclic compounds may be achieved by cycloaddition of the l-trifluoromethyl-3,4-di-hydronaphthalene (113) with diene 12b (Equation 5.13). 

Aryltrimethylsilanes has been found to be a useful complement to direct thallation in the preparation of arylthallium(III) intermediates. The thallium(III) replaces the silyl substituent and the scope of the reaction is expanded to include some EWGs, such as trifluoromethyl. How does the silyl group function in these systems ... 

As indicated in Chapter 3, compounds with fluorines bound directly to a carbon bearing a hydroxyl group are usually very unstable relative to the carbonyl compound plus HF. Nevertheless trifluoromethanol has been prepared, but it spontaneously loses HF at temperatures above -30 °C. Its fluorine and carbon NMR data are given in Scheme 5.8 and 5.11, and they resemble the respective data of trifluoromethyl ethers. 

A trifluoromethyl group bound directly to phosphorous is deshielded slightly more than the respective nitrogen compound (Scheme 5.18). 

Polymorphism has been identified in the KL-(BEDT-TTF)2Cu(CF3)4(DBCE) system [44]. The primary difference between the kl- and KL -phases is that adjacent BEDT-TTF layers in the KL-phase are tilted in opposite directions, while those in the KL-phase are tilted in the same direction. Also similar to the KL-phases, the trifluoromethyl groups in the kl -phase are disordered. These two phases have similar morphologies and EPR line widths [45] and are thus difficult to distinguish from each other. It is currently not known how prevalent the KL -phase is, although it appears to have similar physical properties to the KL-phase. 

Nitrones with alkyl groups bound directly to the 1,3-dipolar moiety fail to react with TMSCF3, but trifluoromethylation of 3,y-unsaturated nitrones such as u-styryl-/V-phenyl nitrone gives the products of trifluoromethylation (Scheme 2.196) (681, 682). 

The direct substitution by a trifluoromethyl group led in most cases to excellent results, as detailed in Table 33.10. 

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