1,2-Dithietane synthesis

A one-pot synthesis of alkyl perfluoroalkyl ketones has been developed. Phosphoranes, generated in situ, are acylated with a perfluoroacyl anhydnde, and the resultmg phosphonium salts are hydrolyzed with alkali [4S (equation 48) Hydrolysis of a carbon-sulfur bond in 2-chloro-2,4,4-trifluoro-1,3-dithietane-S-trioxide, which can be obtained from 2,2,4,4-tetrachloro-l,3-dithietane by fluor-mation with antimony trifluoride followed by selective oxidations, opens the nng to produce 2-chloro-1,1,2-trifluorodimethyl sulfone [49] (equation 49)... 

A. Synthesis of Isolable Dithiiranes 1. From Bridged 1,3-Dithietanes... 

Tlie chemistry of 1,2-dithietanes is still emerging. Isolable and well-characterized 1,2-dithietanes are limited to only two compounds, 3,4-diethyl-l,2-dithietane 1,1-dioxide (77) and dithiatopazine (73).The synthesis of 1,2-dithietanes has been overshadowed by their thermal instability, which arises most probably from repulsive interactions between the lone-pair electrons on the sulfur atoms, as we have already seen in the chemistry of dithiiranes. 

Scheme 6. Photo-induced bridging of bis(thiolactones) synthesis of dithiatopazine (31), the first stable 1,2-dithietane.

The preparation and investigation of the thietane oxide system (5a) is largely associated with stereochemical and conformational studies . The investigation of the thietane dioxides (5b) is substantially related to the chemistry of sulfenes , the [2 -I- 2] cycloaddition of which with enamines is probably the method of choice for the synthesis of 5b . The study of the thiete dioxide system (6) evolved, at least in part, from the recognition that the unstable thiete system 183 can be uniquely stabilized when the sulfur in the system is transformed into the corresponding sulfone , and that the thiete dioxide system is very useful in cycloadditions and thermolytic reactions. The main interest in the dithietane oxides and dioxides (7) appears to lie in the synthetic challenge associated with their preparation, as well as in their unique structural features and chemical behavior under thermolytic conditions . ... 

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. 

One particular class of a,/3 -unsaturated keto-substituted 1,3-dithietanes called desaurins has been known since 1888 (1888CB337). While several specific routes to their synthesis will be outlined later, the one illustrated here (Scheme 110) presumes the intermediacy of an a,/3 -unsaturated keto-substituted thioketone which then dimerizes. The methods used to... 

The methodology based on the reaction of 1,3-dithietanes with quadricyclane 67 was applied to the synthesis of polyfluorinated sulfur-containing polycyclic hydrocarbons. The reactions of 2,2,4,4-tetrakis(trifuoromethyl)-l,3-dithietane 66 with quadricyclane 67 under various conditions gave the cycloadduct 68 in high yields (Equation 9) <2005JFC(126)1332>. 

The synthesis of 1,2-dithietanes has been exhaustively presented by Zoller in CHEC-II(1996) <1996CHEC-II(1B)1113>, where the literature until 1995 has been reviewed. Since this date, only two papers concerning the synthesis of 1,2-dithietanes have been published. 

Synthesis of 1,3-dithietanes may be performed using several routes. They can be obtained by an intramolecular cyclization of dithiocarbonates <2003CC1408>. The cyclization of the ethoxycarbonylsulfonyl derivatives 155 catalyzed by titanium tetrachloride in dichloromethane at room temperature afforded the corresponding derivatives 156 in satisfactory yields (Equation 20 Table 6). 

The synthesis of two isomers of bicyclic dithietanes 157a and 157b is based on the oxidative sigmatropic rearrangement and the [2+2] cyclization of divinylsulfane 158 (Scheme 20 Table 7) <1996JA2790, 1996JA2799>. 

Another reported synthesis of symmetrical spiro-1,3-dithietanes 163a-d substituted with an adamantyl moiety is based on the [2+2] cycloaddition of two molecules of variously substituted adamantane-2-thiones <1997BCJ509>. With methanesulfonic acid as an acidic catalyst, the reaction provided 1,3-dithietanes 163a-d in high yields at ambient temperature. A similar reaction was performed with phosphorus pentachloride as the catalyst (Equation 22 Table 8) <2002AXCo231>. 

Table 8 Synthesis of adamantane-derived spiro-1,3-dithietanes 163a-d (Equation 22)...

A similar synthesis was performed for the dithietane 166 by the room temperature dimerization of pentacy-clo[5.4.02 603 1°0s 9]undecane-8-thione 167. After 10 days, the reaction was complete and dithietane 166 was isolated in 95% yield (Equation 24) <2004TL7655>. 

The synthesis of poly-dibenzylidene-l,3-dithietane 201 is based on the Wittig reaction of/ -xylcnc-bis(triphcnyl-phosphonium) chloride 199 with carbon disulfide <2001MM346, 2002MM3806>. The phosphonium salt 199 was converted to the ylide 200, which reacted with carbon disulfide, yielding, after methanolysis, a thioketene. The latter was stirred at room temperature for 12 h to provide the polymeric compound 201, bearing 1,3-dithietane moieties in 54% yield (Scheme 25) <2001MM346, 2002MM3806>. 

Head-to-tail dimerization of thiocarbonyl compounds to 1,3-dithietanes (Scheme 105) occurs thermally <1977JOC2345> and photochemically <1981JOC3911>, or catalyzed either by a base <1973T2759> or a sulfonic acid <1997BCJ509>. For example, synthesis of dithietane 213 in excellent yield was performed by the room temperature dimerization of the thione 212 (Scheme 106) <2004TL7655, CHEC-III(2.18.4.2)838>. Diaryl thioke-tones are resistant to dimerization. Some thiones dimerize to 1,3-dithietanes <1975BSF(2)1670>. 

The reaction between o-phenylenediamine and an equimolar amount of an aromatic or heterocyclic aldehyde has been shown to proceed by initial formation of a monoanil (74). In the presence of oxidizing agents (e.g. nitrobenzene, which also acts as the solvent) this can form the 2-substituted benzimidazole. With two moles of aldehyde the bis-anil (75) forms, giving rise to a 1,2-disubstituted benzimidazole (Scheme 42). This aldehyde route to benzimidazoles is particularly suited to the synthesis of compounds with a heterocyclic group (e.g. 2-thienyl-, 2-pyridyl-) at C-2. Reaction of 2,2,4,4-tetrakis(trifluoromethyl)-l,3-dithietane with o-phenylenediamine gives 2,2-bis(trifluoromethyl)benzimidazoline (7430785). 

---