Trifluoromethyl-containing compounds

SCHEME 9.2 Examples of fluoro- and trifluoromethyl-containing compounds in... 

Morita Y, Kamakura R, Takeda M, Yamamoto Y (1997) Convenient preparation of trifluoro-acetyl Meldrum s acid and its use as a building block for trifluoromethyl-containing compounds. Chem Commun 1997 359-360... 

An enantioselective, organocatalytic domino Friedel-Crafts aminoalkylation with imines generated in situ from trifluoroacetaldehyde hemiacetal (219) and aniline 220 for the synthesis of chiral trifluoromethyl-containing compounds was reported by Ma and coworkers (Scheme 42.51). Very high activity and selectivity was obtained using chiral phosphoric acid catalysts [109]. 

Besides the above-mentioned catalytic asymmetric hydrogenation method for preparing fluorine-containing compounds, other reactions such as asymmetric reduction of achiral fluorine-containing ketones are also feasible methods for preparing chiral fluorinated compounds. For example, the oxazabor-olidine system, which has been discussed in Chapter 6, can also be employed in the catalytic reduction of trifluoromethyl ketones. Scheme 8 40 depicts some examples.85... 

Each of these synthetic methods is limited to low valent metal complexes in each case at most two CF3 groups have been substituted onto a metal ion. In Section III some of the contemporary approaches that have been designed to curtail the enforced reliance upon only two precursors are indicated and some of the early results from these preliminary studies into the chemistry of trifluoromethyl-containing transition metal compounds are presented. 

Immediately upon their isolation, trifluoromethyl-containing derivatives of (low valent) transition metals were universally found to be much more robust, both thermally and oxidatively, than their methylated counterparts. Many perfluoromethyl complexes, for example, have been found to be unreactive in air whereas the corresponding methyl derivatives are air sensitive. Under anaerobic conditions a number of trifluoromethylated species decompose at temperatures approximately 100°C higher than the analogous methylated compounds. 

Once the trifluoromethyl-containing organometallic compounds have been formed, ligand-exchange reactions usually proceed readily. The first example was reported by Hieber, who observed that NO reacted cleanly with CF3Co(CO)3P(0)3 to afford CF3Co(NO)2P(Ot/>)3 quantitatively (22). 

Bis(trifluoromethyl)mercury was found to react at elevated temperatures with both tin and germanium tetrahalides, resulting in a number of CF3-containing compounds including the fully substituted derivative of germanium, (CF3)4Ge Eq. (5)1. The reaction of tin tetrabromide with (CF3)2Hg, on the other hand, yielded only CF3SnBr3 and (CF3)2SnBr2, as shown in Eq. (6) (102). 

Table 7 Summary of the results obtained for the continuous flow trifluoromethylation reactions of carbonyl-containing compounds...

The purpose of the present review is to examine the current status of the chemistry of trifluoromethyl-containing transition metal compounds where the term transition metal had been defined to include the metals of groups 3-12. The early studies in this area have been discussed previously several times (1-4), and there has been no effort to provide a comprehensive literature coverage of the CF3-metal chemistry that was reported prior to 1980. 

Figure 6.15 Absorption spectra of sulfur containing compounds. Top thiophenol (in heptane, ), thioxanthone (in hexane, ), thiourea (in water, ), bis(trifluoromethyl)thioketene (in isooctane, —).280 Bottom absorption ( ) and emission (—) spectra of adamantanethione in perfluoroalkane solvents.1257 The peak at the red edge of the S0—> Si transition coincides with the 0 0 band of phosphorescence and is attributed to S0—>T-i absorption...

For many years now, the reactivity of trifluoromethyl bromide has been underestimated. During the past decade the major breakthrough in this area has been the realisation that trifluoromethylation of organic compounds with this halide can be induced by mild reductants such as thiolates, zinc or sulfoxylate radical anion. Nowadays, a great variety of fluorinated products are available by these new methods sodium triflinate and triflic acid, trifluoromethylated alcohols, trifluoromethyl-containing aromatic compounds, ethyl trifluoropyruvate, trifluoromethylsulfides. ... 

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