Thioketones thiobenzophenone

We proposed new photometric reagent 4,4 -bis(diethylamino)-thiobenzophenone (ethyl derivative of Michler s thioketone, EMT) for the determination of free chlorine and chloramines in drinking water. 

A ring opening of the dithiirane 39 to the thioketone 5-sulfide 35 was proposed for the reaction of thiobenzophenone 5-oxide (40) with the thioketone 41 (81LA187). Tlie conjugation with the phenyl group would stabilize 35 relative to the dithiirane form. 

Stock solution Dissolve 1 g 4,4 -bis(dimethylainino)thiobenzophenone (Michler s thioketone) in 100 ml chloroform. 

Whenever benzyne is expected to undergo a [2+2] cycloaddition as with ketones,109 it behaves as a dienophile with aromatic thioketones. Reaction of thiobenzophenones with benzyne yields the [4+2] cycloadducts and 1H-2-benzothiopyrans.110,111 Sterically congested thiones,111 thiopivalophenones and 2, react with benzyne to give the [2+2] adducts, 2H-l-benzothietes. 

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. 

Photocycloaddition of thiones to alkenes is the most popular and fruitful method for the preparation of the thietane system. In analogy to the formation of the oxetanes by cycloaddition of the electronic excited ( ,tc ) carbonyls, thietanes can be expected to arise photochemically from aromatic thioketones and substituted olefins as well as 1,2- and 1,3-dienes. ° Thiobenzophenone serves as a source of a sulfur atom and, because of its blue color, which disappears on photocycloaddition, permits exact control over the reaction time. A mixture of thiobenzophenone and a-phellandrene must be irradiated for 70 hr before the blue color disappears (Eq. 2) and... 

Thus, pentacarbonyl(thioketone) complexes [M(CO)5L] were prepared by irradiation of solutions of [M(CO)6] (M = Cr, Mo, W) in the presence of thioketones L (L = thiobenzophenone, adamantanethione)119 [Eq. (4)] and by refluxing solutions of [Mo(CO)6] in tetrahydrofuran (THF) in the presence of L = p,p -disubstituted thiobenzophenones, thiofenchnone, and thiocamphor, respectively.120 The formation of two diastereomers of the thiocamphor complex was observed, probably due to a high inversion barrier at sulfur. Only one isomer of the thiofenchnone complex could be detected. However, fluxional behavior could not be ruled out.120... 

With some complexes, thiobenzophenone coordination is succeeded by an orthometallation. Photolysis of [Re2(CO)io] in the presence of various thiobenzophenones yielded, as expected, the binuclear complexes [Re2 (CO)4V-S = C(C6H4R-/>)2 ] (7). On subsequent thermolysis the monomeric orthometallated thioketone complexes 8 were formed (Scheme 2).125 In the thermal reaction at elevated temperatures the orthometallated com-... 

Modifications of the route described earlier are (a) the conversion of [M(CO)6] (M = Mo, W) into the chloro-bridged binuclear trianions 10, which subsequently react with S = C(C6H4OMe-p)2 to give the thioketone complexes, and (b) reduction of [W(CO)6] by sodium amalgam to give the dianion [W2(CO)i0]2 and treatment of the latter with thiobenzophenones, adamantanethione, or thiocamphor (Scheme 3).128... 

Coordinated olefins are also readily displaced by thioketones, e.g., stil-bene, in the molybdocene complex 14 by thiobenzophenone to form the complex 15 [Eq. (6)].138 Similarly, thiobenzophenone is substituted for ethene in [Rh(C2H4)(PMe3)(7/5-C5H5)] to yield [Rh(PMe3)(V-S = CPh2) ( -C5H5)]. m... 

The H2S/HC1 method of thionation of ketones was efficiently applied in the syntheses of aromatic thioketones, such as thiobenzophenone [129] and hindered aliphatic thiones, e.g. thiocamphor [128, 130] and thiofenchone [128, 131]. The following convenient procedure uses trimethyl orthoformate as a co-reactant [128]. 

Barton and coworkers exploited this strategy in the preparation of overcrowded ethylenes456 usually the desulfurization of a thiirane is accomplished by one equivalent of tertiary phosphine, mainly triphenylphosphine. However, spontaneous loss of sulfur from thiiranes substituted by aryl or halogen has sporadically been reported. Huisgen has reviewed this subject455 and performed many kinetic studies. He found that the desulfurization step can be accomplished by catalytic thiolates and also by thiobenzophenone or other thioketones, although in this case the reaction is slower (equation 131). 

The thiirane donates sulfur to the thioketone, thus furnishing olefin and thiobenzophenone 5-sulfide (122) which can be intercepted in 1,3-dipolar cycloadditions to activated acetylenes or thiones455. 

Type II intermolecular ene reaction of thioaldehydes was reported by Vedejs and coworkers492 and already mentioned by Schaumann1. Type in has recently appeared and involves the formation of a C—S bond instead of a C—C bond, as in the case of type I. Type III intramolecular ene reaction has been reported for thioketones and for thioaldehydes. The group of Motoki489 examined the thermal cyclization of o-(2-substituted allyloxy) thiobenzophenones 137 leading to 1,5-oxathiocine derivatives 138 (equation 148). 

It was mentioned earlier that thiocarbonyl thiolates reacted with thioketones forming 1,2,4-trithiolates <1987JA902>. Aromatic thioketones (e.g., thiobenzophenone) are super-dipolarophiles and at 80 °C in a three-reagent mixture with phenyl azide and cyclobutanethiones they form spiranic compounds with X = CO, CS, or CH2 (Equation 21) <1995HCA1298>. An X-ray study of the compound with Ar = 4-MeOC6H4 confirmed the molecular stmcture. 

An attractive reagent for the transformation of ketones into thioketones has been introduced by Degl Innocenti and co-workers [74, 75]. The commercially available bis (trimethylsilyl) sulfide works efficiently at room temperature, with catalysis of CF3S03SiMe3 in acetonitrile, for the production of aromatic thiobenzophenones, adamantanethione and 2-cyclenethiones. 

The main drawback in the use of thiocarbonyl compounds as spin traps was represented by the fact that in most cases the resulting spin adducts either were as transient as the attacking radicals (aliphatic thioketones and dithioesters) or were characterized by very complex ESR spectra (thiobenzophenone and its derivatives). It was only after the introduction of thiobenzoyltriphenylsilane la that the use of thiocarbonyl compounds in spin trapping experiments acquired some practical value. 

Thiobenzophenone 5-sulfide (35) was successfully generated by a cycloreversion of the 1,2,4-trithiolane 36 at 60°C or by a sulfur transfer from thiiranes to thiobenzophenone (87JA902 97T939).The thioketone 5-sulfide... 

Gotthardt and Lenz reported the diastereodifferentiating thietane formation in the photocycloaddition of thiobenzophenone 13 and xanthione 14 (Scheme 6) with (- )-menthyl methylacrylate 15 [88]. The photochemistry of thioketones is wavelength dependent, involving both excited triplet (TJ and singlet (S2) states that undergo independent processes. It was seen that the des obtained were greater (18%) for the product from the T] state than that from the S2 state. In-depth discussion of this topic is to be found in Chap. 5. 

The stability of the 2,5-dihydrothiadiazole 5-oxides depends on the nature of each substituent. For example, cycloaddition of aromatic thioketone 5-oxides, such as thiobenzophenone 5-ox-ide or thiofluorenone 5-oxide, with diazopropane results in the formation of 2,5-dihydrothiadiazole 5-oxides in high yield. Diazomethane reacts more sluggishly and a complex mixture containing various products is formed78,79. 

---