Thioxanthones synthesis

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... 

Ring synthesis by y- closure is a somewhat more versatile entry into this class of compound, though even then it is restricted to suitably activated precursors such as (142) (equation 101) (72T5197). Thiochromones and thioxanthones are probably most frequently prepared by this mode of closure, usually via an intramolecular Friedel-Crafts condensation of a carboxylic acid with an aromatic ring (equation 102) (71GEP2006196). 

The same metallation methodology features in a synthesis of 1-dimethylaminothioxanthone 10,10-dioxide. A key step is the introduction of a 6-phenylsulfonyl group into 2-dimethylamino-A iV-diethylaminobenzamide by directed metallation (Scheme 208) <2002JOC3585>. Other substituted thioxanthone 1,1-dioxides have been accessed by the directed metallation of diarylsulfone 2-carboxamides (Equation 188) <1994JOC6508>, a neat variant on the standard route to xanthones by the cyclization of benzoic acids. 

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>. 

Both xanthones and thioxanthones are available through CsF-promoted coupling of arynes with salicylates and thiosalicylates. The synthesis proceeds through sequential intermolecular nucleophilic substitution and intramolecular electrophilic cyclisation (Scheme 39) <07JOC583>. The Pd-catalysed annulation of 3-iodoflavone with the same triflate results in the dibenzo[a,c]xanthone (Scheme 39) <07JOC223>. 

A further interesting feature of the polymeric photoinitiators is based on the possibility of anchoring different photosensitive moieties to the same macromolecule in order to provide a synergistic effect on activity due to their interaction along the polymer chain. In this context, the synthesis of several copoly-meric photoinitiators bearing side-chain thioxanthone and hydroxyalkylphenone or morpholino ketone moieties has been reported recently [156]. In particular, the free radical copolymerization of 2-[2-(acryloyloxy)ethylthio] thioxanthone (AETX) with either [4-(2-acryloyloxyethoxy)phenyl]-2-hydroxy-2-propyl ketone (HPA) or [4-(2-acryloyloxyethylthio)phenyl]-2-(iV-morpholino)-2-propyl ketone (APMK) [poly(AETX-co-HPA) and poly(AETX-co-APMK), respectively] and of 4-[2-(methacryloyloxy)ethoxycarbonyl] thioxanthone (METX) with APMK [poly(METX-co-APMK)] has been performed. 

A century of thioxanthones Through synthesis and biological appHca-tions 13CMD2438. 

A Method for Catalytic Synthesis of Convenient Thioxanthone Crown Ethers Using Wells-Dawson, H EP WijO ], Preyssler Hj lNaPjWj O,],... 

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],... 

Scheme 3.21 Synthesis of thioxanthone crown ethers using green method...

Gharib A, Jahangir M, Seheeren JHW (2010) A method for catalytic synthesis of convenient thioxanthone crown ethers using Wells-Dawson, H [P2W,j0 j] and Preyssler Hj lNaPjWjjOjjii], heteropolyacid catalysts. Bulg Chem Commun 42 214-221... 

J. Zhao, R.C. Larock, One-pot synthesis of xanthones and thioxanthones by the tandem coupling-cyclization of arynes and salicylates, Org. Lett 7 (2005) 4273-1275. 

A high-temperature synthesis of thioxanthene from thiophenol and o-chloro-or o-bromo-toluene has been reported. Irradiation of the thiol esters (44 X = Cl, Br, I, or SOgMe Y = H) afforded the thioxanthone (45 Y = H) and p-tolyl disulphide. This rearrangement is believed to involve a 1,3-shift of the SCgHgMe group. When the dichloro-compound (44 X = Y = Cl) was irradiated, photosubstitution occurred, giving the sulphide (45 Y = p-Me-CgH4S) instead of the expected chloride (45 Y = Cl). The same product was... 

Compounds in which other heterocyclic rings (pyrazoles, isoxazoles, imidazoles ) are fused to thiopyrans have been described. The interesting thiazolium salts (56) were prepared by allowing the betaines (55) to react with 4-thioxothiazolidin-2-ones. Application of the Fischer indole synthesis and the Friedlander reaction to tetrahydrothiopyran-3-one led to the exported indolo-and quinolino-derivatives. Ring closure of (57) under acidic conditions afforded the rearranged product (58). Syntheses of benzothiopyrano[4,3,2-flfe]-quinazolines (59) from 1-amino-thioxanthones and of their S- and 7V-oxides have been described. ... 

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