Reaction with hexafluorothioacetone

Thioketones, such as thiofluorenone, hexafluorothioacetone and perfluorocyclobutanone, add to a variety of 1,3-dienes to give dihydrothiapyrans (e.g. equation 24)25. Styrene yields a 1 2 adduct with hexafluorothioacetone (equation 25)25. The reactions of thioace-tophenone and thiobenzophenone with isoprene and 2-chlorobutadiene yield mixtures of regioisomers in quantitative yields (e.g. equation 26)26. 

Hexafluoroacetone imine has been prepared by the reaction of hexafluoroacetone with triphenyl phosphine imine,2 by the pyrolysis of N-phenyl-2,2-diaminohexafluoropropane,23 by the reaction of hexafluorothioacetone with hydrazoic acid,4 and by the reaction of ammonia and phosphorus oxychloride with hexafluoroacetone.4,5 The latter method, which is described here, is the most convenient for it does not require preparation of several intermediates or use of pressure equipment. This method has also been used to prepare the imines of other Huoroketones, including the imines of chloropentafluoroacetone, dichlorotetrafluoroacetone, and perfluorodiethyl ketone.5 Substitution of methylamine for ammonia in this procedure gives the N-methyl imine.5... 

The assumption that such reactions occur via thiadiazoline intermediates received direct support when 84 was isolated in 92% yield from the reaction of bis(trifluor-omethyl)diazomethane (83) with hexafluorothioacetone. Refluxing 84 afforded perfluorotetramethylthiirane (85) in 95% yield. 

SCHEME 2.22 Cycloaddition reaction of quadricyclane (12) with hexafluorothioacetone and bis(trifluoroniethyl)thioketene. 

The stable, sterically crowded hexafluorothioacetone 5-imide (44) reacts smoothly with aromatic thioketones, but the reaction with 1 requires elevated temperatures. Unexpectedly, the product isolated after 3 h at 100 °C is 1,4,2-dithiazolidine (47). Its formation can be rationalized by the isomerization of 44 to give thiaziridine 45 being in an equilibrium with thionitrone 46, which then traps 1 to yield 47 (eq 19). 

The dimer of hexafluorothioacetone (217) reacts, as shown in Scheme 8, with mercuric fluoride-potassium fluoride to give the mercuric mercaptide of perfluoropropane-2-thiol in DMF, potassium flucnide promotes the reaction of (217) with alcohols, thiols, thiophenols, and olefins to give products derived from the thioacetone monomer. Reaction with styrene gave the bis-Diels-Alder adducts (218) and (219) thietan (220) is obtained with cyclohexene. Amino-alcohols, o-aminophenol, o-aminothiophenol, and o-phenylenediamine yield 2,2-bis(trifluoromethyl)-l,3-het ocyclic derivatives, e.g. (221). 1,3-Dithietans did not react with Fe2(CO) and were discarded as possible intermediates in the ortho-metallation reactions of thiobenzophenones. The hydrolysis reactions of a 1,3-cyclodisiladithietan and its reaction with o-hydroxymercuribenzoic acid have been investigated. ... 

Many cycloaddition reactions have been carried out with ketenes and thioketones. The products are thiolactones (52). Hexafluorothioacetone and diphenylketene, however, do not undergo cycloaddition even after prolonged heating at 100°C. Good results can be obtained when the more stable dimer of this fluorinated thioketone (53) is used. Anionic monomer 54 could be released by the action of potassium fluoride in an aprotic solvent. Two-step cycloaddition to diphenylketene yields ketone 55. 

With slight modification, the methods used to prepare fluorothioacyl fluorides can also be used for synthesis of fluorothioketones. Hexafluorothioacetone, the member of this class that has been studied most extensively, is readily obtained by high-temperature reaction of hexafluoropropylene and sulfur (53). The thio-ketone is a deep-blue liquid, bp 8° C, that dimerizes on standing to 2,2,4,4-tetrakis-(trifluoromethyl)-l,3-dithietane. 

The reaction of a perfluoromercurial with sulfur is particularly well suited to synthesis of hexafluorothioacetone. The first step is addition of mercuric fluoride to hexafluoropropylene in liquid HF which gives bis(hexafluoroiso-propyl)mercury. 

Fluorothioketones are more difficult to polymerize. There are two reasons. First, agents that promote polymerization also catalyze dimerization to dithi-etanes, which is a very fast reaction. Second, ceiling temperature of polymerization is low with the result that polymer decomposes back to monomer as it is being isolated. However, poly(hexafluorothioacetone) can be formed at very low temperatures by initiation with dimethylformamide or BF3 etherate, even though at — 78° C the only product isolated is 2,2,4,4-tetrakis(trifluoromethyl)-l,3-di-thietane. 

Since it has been shown that this reaction generally gives 2-thietanones ( 3-thio-lactones), reports of 3-thietanones being formed should be treated skeptically (See Section XIII.3.B.). The chemical reactions and mass spectrum of the adduct of hexafluorothioacetone with diphenylketene have been interpreted on the basis of a 3-thietanone. ... 

In a paper dealing with the reactions of methylenediphosphines with hexa-fluoroacetone (HFA) and hexafluorothioacetone (HFTA) dimer, Roschenthaler... 

The most easily accessible compounds of this class are 1,3-dithietanes. They are formed by a spontaneous dimerization of fluorinated thioketones or acyl halides. Thus, hexafluorothioacetone 34, generated in the reaction of bis(perfluoroisopropyl) mercury with molten sulfur at about 450°C (Scheme 2.18), undergoes at ambient temperature slow dimerization to form dithietane 35. This dimerization is significantly accelerated by catalytic amount of base, such as pyridine. At elevated temperature, the dimer 35 can be converted back into 34. 

The uncatalyzed reaction of 43 with quadricyclane (12) proceeds readily to give the exo-adduct 46 (Scheme 2.22). Analogous cycloaddition with formation of adduct 47 was also observed for hexafluorothioacetone generated in situ from dithietane 35 (Scheme 2.22). ... 

Synthetic applications of dithietane 35 are not limited to its use as a source of hexafluorothioacetone. This compound is also a valuable precursor for the synthesis of a variety of fluorinated sulfur-containing derivatives. For example, the pyrolysis of 35 at 325 C results in the high-yield formation of (CF3)2C=C(CF3)2. The reaction of 35 with PhaP was found to be a convenient route to (Ph)3P=C(CF3)2, which was used for the preparation of l,l-bis(trifluoromethyl) alkenes and CF2=C(CF3)P(0)(0R)2. Recently reported transformation of fluorinated thietanes involves reductive ring expansion to substituted dihydrothiophenes. For example, the treatment of compound 47 with aluminum powder in the presence of a catalytic amount of PbCl2 resulted in an interesting ring expansion process leading to the formation of compound 48 in excellent yield (Scheme 2.23). Readily available fluorinated cycloadducts 49... 

Bicychc 2,2-bistrifluoromethyl thiepine 123 is synthesized in moderate yield by CsF-catalyzed reaction of cycloheptadiene-1,3 with the cyclic dimer of hexafluorothioacetone (Fig. 10.47). ... 

CF2 CFa CF2 CF SAg (not isolated) -- (with EtI at 75 °C) CF2 CF2 CF2 CF SEt (21%). Raman and photoelectron spectral data are available for some CFs S-compounds, and so are e.s.r. parameters for the radical CFs S CHs-CBu a [generated via photolysis of a solution of the appropriate olefin in (CFs-S)2]. Unsuccessful attempts have been made to generate a radical anion via electrochemical or chemical (NaK alloy) reduction of 3,4-bis(tri luoromethyl)-l,2-dithieten. i Reactions between trifluoromethanesulphenyl chloride and JV-chloro-amines are portrayed in Scheme 26 (p. 216) and some involving hexafluorothioacetone dimer in Scheme 27 (p. 217) many unsuccessful attempts are claimed to have been made to isolate bis(trifluoromethyl)methanethiol from the products of the reactions of the dimer with amines, the conversion into hexafluoroisopropylidenimines being... 

An AT-ray crystal structure analysis has shown that the product of the reaction of CFs Rh(CO)6 with carbon disulphide is (0Q4ReS2CS[Re(CX ))4]2SCS2Re(C 0)4. The displaced trifluoromethyl groups were found as hexafluorothioacetone in the reaction mixture. ... 

The reaction of aromatic thiones as dipolarophiles with Af-(l-adamantyl) hexafluorothioacetone 20 affords the [3+2] cycloadducts 21 in good yields . 

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