5- dibenzothiophenium

Perfluoroalkyl)dibenzothiophenium and -selenophenium Salts and Their Analogs (93JA2156)... 

The S- and Se-(perfluoroalkyl)dibenzothiophenium salts 17-27 were synthesized according to three methods (Eq. 4) (1) fluorination of the corresponding sulfide 1-6 or 8 or selenide 11 or 12 with F2 in the presence of an acid or a Lewis acid (2) fluorination with F2, followed by treatment with an acid or a Lewis acid and (3) treatment of sulfoxide 13, 14, or 15 or selenoxide 16 with triflic anhydride (Tf20). Sulfoxides 13-15 and selenoxide 16 were prepared by oxidation of the corresponding sulfides or selenide with m-chloroperbenzoic acid. 

C. Nitration of S-, Se-, and Te-(Perfluoroalkyl)dibenzothiophenium, -selenophenium, and -tellurophenium Salts (93JA2156)... 

All the S-, Se-, and Te-(perfluoroalkyl)dibenzothiophenium, -selenophenium, and -tellurophenium salts synthesized above are stable crystalline materials at room temperature. Their melting or decomposition points (dec. p) are higher than 100°C. Nitro substituents decrease their stability [S-salt 17 mp 155°C > dinitro S-salt 39 dec. p 130-135°C]. The chalcogen stability increases in the order S < Se < Te [dec. p S-salt 39 130-135°C < Se-salt 40 198-200°C < Te-salt 41 275-280°C]. Thermolysis of S-salt 17 at 200 C gave trifluoromethyl triflate (50) and dibenzothiophene (51) in high yields (Eq. 12). Thermolysis of dinitro S-salt 39 at 140°C gave 50 and dinitrodiben-zothiophene 52 (Eq. 13). 

Fig. 1. Relationship between F CF3 chemical shifts of S-, Se-, and 7e-(trifluoromethyl)-dibenzothiophenium, -selenophenium, and -tellurophenium triflates and Hammett s constants Om or (Tp for the ring substituents S, Se, and Te refer to substituted and unsubstituted S-, Se-, and Te-(trifluoromethyl)dibenzothiophenium, -selenophenium, and -tellurophenium triflates, respectively. The numbers on the lines are the compound numbers shown in the text. Substituents and their substitution positions are shown in the parentheses. The smaller the F NMR chemical shift is, the more downfield is the resonance (CFCI3 served as an internal standard in CD3CN).

Kinetic Parameters for the Trifluoromethylation of Aniline with 5-(Trifluoromethyl)dibenzothiophenium Triflate (17), S-(Trifluoromethyl)diphenylsulfonium Triflate (29), AND 5-(Trifluoromethyl)-3,7-DINITRODIBENZOTHIOPHENIUM TrIFLATE (39) IN DMF-d7 AT 25°C... 

Perfluoroalkyl)dibenzothiophenium salts and their selenium and tellurium analogs are novel perfluoroalkylating agents. The synthesis and reactivity of these compounds are covered by T. Umemoto (Ibaraki, Japan). Finally, the first detailed survey of the chemistry of 1,3-oxazinium and 3-azapyrylium salts for over twenty years is provided by S. Lukyanov (Rostov-on-Don, Russia). 

In Eq. (7-17), k and are the speeifie rate eonstants of SnI solvolysis of the 5-methyl-dibenzothiophenium ion in a given solvent and in a standard solvent (Et0H/H20, 80 20 cL/L At = 0), respeetively. At values are known for 37 pure and binary solvents and span a range from At = -5.26 [(CF3)2CH0H/H20, 97 3 cg/g] to +0.37 (EtOH) [305, 308]. The At solvent nueleophilieity seale ean be used directly to correlate the solvolytic behaviour of other RX+ substrates with a neutral nueleofuge, and also in appHcations of the extended Grunwald-Winstein equation (7-15). Many examples of the use of Nj values in the correlation of specific rates of solvolysis of a variety of RX and RX" " substrates are given in reference [305]. 

Umemoto s reagents are soluble and stable in a variety of polar solvents, for example DMSO, DMF, acetonitrile, THF, or CH2CI2. A side product ofthe trifluoromethylation of any nucleophile is the formation of one equivalent of dibenzofuran, which is sometimes difficult to separate from the desired reaction product. To facilitate the work-up, zwitterionic dibenzothiophenium sulfonates were designed. 

A wide range of nucleophilic substrates of different reactivity were trifluoromethylated with these reagents. The substrates include carbanions, activated aromatics, heteroaromatics, enol silyl ethers, enamines, phosphines, thiolate ions and iodide anions. " (Scheme 3.8) The least reactive substrates, such as triphenylphosphine, aniline and phenols, require the use of the most reactive dinitro derivative. Most of the reactions can be conveniently performed with the unsubstituted 5-trifluoromethyl dibenzothiophenium salt (35). The least reactive sulfonium salts are the acyclic sulfonium compounds which reacted only with the sodium thiolates.55,59... 

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