Thiobenzophenones, formation from

Flash vacuum pyrolysis (FVP) of 1,3-dithiolane 1-oxides (88-90), as a possible route to thiocarbonyl compounds, has been studied.57 Thiobenzophenone and thiofenchone are obtained from (88) and (89), respectively, but there was no evidence of heptane-4-thione formation from (90). A stepwise homolytic cleavage has been proposed. 

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... 

Like many other 1,3-dipoles (e.g., nitrile ylides, imines, and oxides) (7), thiocarbonyl ylides undergo head-to-head dimerization to give sterically crowded 1,4-dithianes. The first reported example involves the formation of 2,2,3,3-tetraphenyl-l,4-dithiane (18) from thiobenzophenone (5)-methylide (16) (17,28) (cf. Scheme 5.3). Other (5)-methylides are known to form analogous 1,4-dithianes (e.g., thiofluorenone (5)-methylide yields 172) (17). The (5)-methylides of 4,4-dimethyl-2-phenyl-l,3-thiazole-5(4//)-thione (105) and methyl dithiobenzoate (60,104) dimerize to give compounds 173 and 174, respectively. 

Tetraphenyl-l,2,4-trithiolane 221 precipitated with a yield of 84% from a solution of 3-methyl-2,2-diphenylthiirane 220 (R = Me) and thiobenzophenone in a twofold molar excess kept in ether at room temperature during 3 weeks. In the mother liquor, 1,1-diphenylpropene was present in 90% yield. It was concluded that the 1,2,4-trithiolane has a remarkable formation tendency (Scheme 73) <1997T939>. 

Triphenylthiopyrylium salts have been employed as efficient electron transfer photosensitizers to promote the [4+2] cycloaddition between thiobenzophenone and substituted styrenes. A radical cation derived from the thiobenzophenone is involved in the formation of separable diastereoisomeric mixtures of 1,3,4-trisubstituted isothiochromans <2007OL3587>. Interest has been maintained in the photosensitizing properties of thiopyrylium salts for blood disinfection <2007BMCL4406>. Several new thioxanthylium salts have been reported <2007JOC2647, 2007JOC2690>. 

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. 

Thiocarbonyl S-SulSdes (ThiosulSnes). The formation of the symmetrical 1,2,4-trithiolane (34, eq 14) is the evidence for the intermediacy of thiosulfine 33 formed by a sulfur transfer from thiaziridine 31 to 1. The mixed 1,2,4-trithiolane (51) (eq 22) can result either from the [2 + 3]-cycloaddition of thiobenzophenone 5-sulfide (53) with 1 or from 33 with thiobenzophenone. Both pathways are conceivable for the formation of 51 in a three-component reaction including 1, thiobenzophenone, and phenyl azide. Tetraphenyl-1,2,4-trithiolane (54) undergoes a [2 + 31-cycloreversion and releases 53, which is trapped by 1 to afford 51 (eq 22). The latter is stable under the reaction conditions. ... 

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