Thioxanthone reaction scheme

Diaiyl sulfide templates have also been used to direct chlorinations. The selectivities indicate that the chlorine atom is bound to the sulfur, but the yields are not as good as those with aryl iodide templates. The problem is that the sulfur gets oxidized under the reaction conditions. As expected, a thiophene ring is more stable to oxidation and its sulfur atom can still bind chlorine in a radical relay process." The best sulfur template so far examined is the thioxanthone system (Scheme 20). Thus with 3 equiv. PhICh compound (18) undergoes directed C-9 chlorination in 100% conversion, affording a 71% yield of the A iO-alkene sifter base treatment, along with some polar products from excessive chlorination. The thioxanthone template can be recovered unchanged. 

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>. 

Application of the Corey-Fuchs olefination to thioxanthone affords the 1,1-dibromoalkene 366 from which the 1,1-bis(trimethylsilylethynyl)alkene can be obtained by a double Sonogashira coupling reaction. Desilylation yields the 1,1-diethynylalkene (Scheme 86) <2004JA3108>. 

In the presence of a strong base, trifluoromethylacetophenone trifluoromethylates thioxanthone a haloform reaction is involved <2003TL1055>. l-(Af-benzylpiperazino)-2,2,2-trifluoroethanol and iV-trifluoroacctyl-iV-benzyl-piperazine behave in a similar manner (Scheme 88) <2001EJ01467, 2003SL230>. 

Bromine-lithium exchange applied to the sulfide obtained from the reaction between 2-fluorobenzonitrile and 2-bromothiophenol promotes an intramolecular attack on the nitrile function. Hydrolysis of the resulting tricyclic lithio-imine produces thioxanthone (Scheme 209). Alternatively, the imine can be trapped with electrophiles... 

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>. 

Xanthone (34) and thioxanthone (35) are smoothly reduced with diborane in tetrahydrofuran at 0 °C to give the correspxjnding xanthenes (36 and 37). The ease of this reaction is explained by the formation of a stable xanthonium ion (38), generated by elimination of the borate ion (Scheme 11). ... 

HPAs were used as an effective catalyst for the synthesis of thioxanthone crown ethers from the reaction of thiosahcylic acid and benzocrown ethers. This reaction was carried out subsequently via intramolecular electrophilic cyclization. The reaction was in mild and clean conditions, and has high selectivity with good yields (Scheme 3.21) [61],... 

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