Thioxanthone reduction

TABLE 5. Reduction potentials (volt) of thioxanthone (TOS) and its oxides (TOSO, T0S02) compared with that of fluorenone (FIO)... 

The thioxanthone ring system comprises the nucleus for two of the more efficacious orally active antischitosomal drugs. One synthesis for these compounds starts with the chlorsulfonation of pora-chlorotoluene (21-1) to give the sulfonyl chloride (21-2). Treatment of the product with zinc in aqueous sulfuric acid leads to a reduction of the sulfonyl chloride to form the thiophenol (21-3). The key to the formation of this and related thioxanthones and xanthenes consists of the UUman reaction, which... 

The reduction of thioxanthone with LiAlD4 and A1C13 yields 9D-thioxanthene (93%) mp 147-148 °C and similar treatment of thioxanthen-9-ol affords the 9D,9H-thioxanthene. Reaction of thioxanthone with PhLi and the usual aqueous work-up yields 9-phenylthioxanthen-9-ol from which the 9-phenyl-9D-thioxanthene and the corresponding 9H-derivative 356 were obtained. Reaction of 356 with -BuLi and C02 gives 9-phenylthioxanthene-9-carboxylic acid (Scheme 80) <1998JPH(113)53>. 

The reaction of thioxanthone with various 3-thienyllithium compounds is the initial step in the synthesis of the diols such as 602 from which the bis(thioxanthylium) dication 603 is obtained. This species functions as a reversible redox pair with its reduction product, the hexaarylethane, creating an electrochromic system in which electron transfer brings about bond making and bond breaking. These oligomers 604 may be considered to be a new class of molecular wires (Scheme 238) <2004OL2523>. 

A potentially useful chemoselective dissolving metal reagent for the reduction of aromatic ketones in the presence of other functional groups is the combination Zn-DMSO and aqueous potassium hydroxide. In three examples (benzophenone, fluorenone and 4-benzoylpyridine), the yields of secondary alcohols were over 90%. Two other ketones (xanthone and thioxanthone) gave mixtures of alcohol and the hydrocarbon obtained by hydrogenolysis of a carbon-oxygen bond. ... 

Thioxanthene, Thiaxanthene dibenzothiopyran dibenzopenthiophene diphenylenemethane sulfide. C1 H10S mol wt 198.27. C78.75%, H 5.08%, S 16.17%. Conveniently obtained from thioxanthone in 74% yield by reduction wth lithium aluminum hydride Mustafa, Hilmy, J. Chem. Sot 1952, 1345,... 

Several studies were carried on the relationship between the chemical structures of ketones and of amines and the rates and efficiencies of photoreductions. It was observed, for instance, that Norrish I reaction of aromatic ketones is affeeted by electron donating and electron withdrawing substituents of the aromatie portions of the ketones. That, of course, is a result of stabilization or destabilization of the partial eharges in the transition state by the substituents. The rates of eleetron transfer reaetions in photo reduction of various ketones, like benzophenone or thioxanthones and their derivatives by some amines can be found in the literature. Some examples are listed in Table 2.5. 

It has been shown that the product obtained by the action of phosphorus pentachloride on thioxanthone is the thioxanthylium salt (85). Reduction of thioxanthylium perchlorate with zinc (in the absence of oxygen) gives the bimolecular product (86), but with 9-phenylthioxanthylium perchlorate... 

Other papers on thioxanthene derivatives deal with the methylation, on sulphur and sulphoxide-oxygen respectively, of thioxanthene and thio-xanthone sulphoxide, the Beckmann rearrangement of thioxanthone oxime, and the quantitative reduction of thioxanthene sulphoxide to thioxanthene with sodimn borohydride-cobalt chloride, a reagent which appears to be of fairly neral applicability. ... 

The reduction potentials for S,S-dialkyl-S-(hydroxyphenyl) sulfonium salts do not appear to have been measured. These sulfonium salts do not undergo electron transfer photosensitization. Rather, photosensitization has been achieved using typical diaryl ketones such as benzophenone, Michler s ketone, and thioxanthone as photosensitizers. Strongly acidic solutions are produced during photosensitized photolysis, suggesting the formation of a protonic add as one of the products. 

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