Thiobenzophenone adduct

The adducts 41 from 1 and ketones or thiobenzophenone undergo interesting photochemical cycloreversion to afford a silanone or silanethione intermediate 42 in addition to silene 43 both of these intermediates are trapped by ethanol, as shown in Eq. (14).68 71 In the reaction with the thiobenzophenone adduct 41 (R = Ph, X = S), the intermediate silene 43 (R = Ph) was detected by Si NMR.71... 

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. 

Numerous examples involving the preparation of tetrahydrothiophenes via [3 + 2] cycloaddition of thiocarbonyl ylides with electron-poor alkenes have been reported. Thiobenzophenone (5)-methylide (16), generated from 2,5-dihydro-1,3,4-thiadiazole (15) and analogous compounds, react with maleic anhydride, N-substituted maleic imide, maleates, fumarates, and fumaronitrile at —45°C (28,91,93,98,128,129). Similar reactions with adamantanethione (5)-methylide (52) and 2,2,4,4-tetramethyl-3-thioxocyclobutanone (5)-methylide (69) occur at ca. +45°C and, generally, the products of type 70 were obtained in high yield (36,94,97,130) (Scheme 5.25). Reaction with ( )- and (Z)-configured dipolaro-philes stereospecifically afford trans and cis configured adducts. 

A-Sulfinylamines (R—N=S=0) are known to function as reactive dienophiles and dipolarophiles, and some examples of [3 + 2] cycloaddition with thiocarbonyl ylides have been reported (176). For example, the reaction of thiobenzophenone (5)-methylide (16) with both A-phenyl and N-tosylsulfinylamines occurs regiose-lectively to give 1,3,4-dithiazolidine 3-oxides (135). In the case of thiocarbonyl ylide 69, reaction with N-phenyl sulfinylamine selectively afforded the analogous product 136 (R = Ph). However, the corresponding reaction with Al-tosyl sulfinylamine resulted in a mixture of the N,S-adduct (136) (R =Tos) and the 0,S-adduct 137. Formation of a mixture of products is compatible with a stepwise reaction via a zwitterionic intermediate. 

The 1,3-dipolar cycloaddition of the carbonyl ylide (31) to the aldimine (32) produces the adduct (33), which has been used to synthesize the taxol C(13) side-chain (34), which is known to be required for the antitumour activity of taxol (Scheme 9).35 The dirhodium tetraacetate-catalysed decomposition of l-diazo-5-phenylpentane-2,5-dione (35) yields the carbonyl ylide (36), which cycloadds to methylenecyclopropanes (37) to produce spirocyclopropanated 8-oxabicyclo[3.2.1]octan-2-ones [(38)-(40)] in 6-75% yields (Scheme 10).36 The 1,3-dipolar cycloadditions of aliphatic or alicyclic thiocarbonyl ylides with thiobenzophenone produce both regioisomeric 1,3-dithiolanes as expected. However, in the case of highly sterically hindered thiocarbonyl ylides, methylene transfer leads to the formation of 4,4,5,5-tetraphenyl-l,3-dithiolane.37,38... 

Both thiobenzophenones and thiofluorenones undergo [4+2] cycloadditions with acyclic and cyclic 1,3-dienes to give 3,6-dihydro-2//-thiopyrans (Scheme 141). The thiofluorenones are more reactive, even yielding adducts with electron-deficient cyclopentadienes at room temperature. In all cases, the progress of the reaction can be followed by the loss of color of the thione. Unsymmetrically substituted dienes show good to excellent regioselectivity. 

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. 

Tetrachloro-l, 3-dithietane forms a bis adduct with mercury (I) nitrate,whose structure was investigated by IR and Raman spectra. A cyclo-pentadienyl manganese(0) dicarbonyl complex of the dimer of 2,3-diphenylcyclo propenethione has been reported. Raney nickel desulfurizes the tetraester 538 and the desulfurization of the questionable dithietanes obtained by dimerization of thiofluorenone and thiobenzophenone give, respectively, bis-fluorenylidene and tetraphenylethylene. The electrochemical oxidation of 1,3-dithietane has been investigated. 2,2 -[Oxybis(methylene)]bis-l,3-dithietane is inert to boron trifluoride etherate after 30 days at room temperature. ... 

The thermolabile adduct between vanodocene and thiobenzophenone, 23 (see Section II,A,2), converts to diphenylfulvene by internal desulfurization of the modified thioketone ligand (49). 

The reactions of thiobenzophenone are varied. In the imidoylcobalt-ace-tone adduct 134, it displaces the acetone to form complex 135, which is... 

The allylsulphonium salt (209) is recommended as a synthetic equivalent of the unstable allyl trifluoromethanesulphonate. Treatment of methyl diazoacetate with an excess of thiobenzophenone yields a mixture of the dithioles (210) and (211) by way of the thiocarbonyl ylide Ph2C=S—CHCO2-Me. The resistivities and magnetic susceptibilities of the radical-anion salts (212 R, R = H, Me, or Ph n = 1 or 2) have been measured. The meso-ionic 1,3-dithiolium 4-oxide (213) forms the intramolecular cyclo-adduct... 

Reactions take place between thiobenzophenone and hydrogenphosphonothioates or hydrogenphosphinothioates (Scheme 4) (R = R = OEt R = OEt, R = Et or Ph Z = O or S) at 110 °C in the absence of a catalyst or, more commonly, at room temperature in the presence of a basic catalyst such as NaOEt or Et2NH particularly in the latter circumstances, the initial adducts are non-isolable since they undergo rapid rearrangement to S-diphenylmethyl esters. ... 

Bis(trifluoromethyl)-l,2,4,5-tetrazine 314 reacts with substituted thiobenzophenones by [4-h2] cycloaddition via a Diels-Alder adduct which is not isolable. Cycloreversion, with elimination of nitrogen, then gives 6/f-l,3,4-thiadi-azines 315 in yields of 47-75% (Scheme 41) <1998EJ02861>. Similarly, the treatment of 314 with alkylthioformates yields 2,5,6-substituted-6/f-l,3,4-thiadiazines <1984AGE890>. 

Treatment of 1,2,4,5-tetrathiane 55 with DMAD in refluxing mesitylene produced the benzothiopyran 148, that is, the Diels-Alder adduct of thiobenzophenone and DMAD (Scheme 19). When the reaction was carried out in chloroform in a sealed tube at 150 °C, a 36% yield of 148 was obtained, along with 26% of dithiole 149, perhaps via a competing acid-catalyzed pathway <1997H(45)507>. 

Photochemical (589 nm) addition of thiobenzophenone at 40 °C to tetramethylallene (59) gives 2,4,4-trimethyl-3-(diphenylmethylthio)buta-diene (60) as major product, with the cyclo-adduct (61). ... 

Thiobenzophenone undergoes an addition reaction with dienes to yield A -dihydrothiopyrans (4 R = H or Me). The butadiene adduct (4 R = H) is methylated by treatment with butyl-lithium-methyl iodide in THF at - 80 °C to give the 2-methyl derivative, but similar methylation... 

Several papers deal with the chemistry of benzo-2i/-thiopyrans of general type (69). The photoaddition reaction between thiobenzophenone and methoxyallene gives a mixture of a thietan derivative and the thiopyran (70), which rapidly isomerizes at 140 C to the 2/f-thiopyran (71). In a similar way, acetylenes add to thiobenzophenone to give products formulated as (72 R = Ph, CO2H, or CHaOH). Enamines of type (73) are converted thermally into benzo[c]thiophens (isothionaphthenes) (74), which form adducts with A -phenylmaleimide. ... 

The formation of 1,3-oxathiolane with chloral and 1,3-dithio-lanes with cycloaliphatic thioketones occurs regioselectively to yield the sterically less hindered products. On the other hand, aromatic thioketones, e.g., thiobenzophenone or 9/ fluorene-9-thione, intercept 8 to give comparable amounts of both regio-isomeric adducts. Usually, stereoisomeric dipolarophiles such as fumaronitrile and maleonitrile as well as dimethyl fumarate and maleate form 18 in a stereoselective manner. However, in the case of extremely electron-poor dipolarophiles, e.g., dimethyl 1,2-dicyanofumarate or ( )-l,2-bis(trifluoromethyl)ethylene-l,2-dicarbonitrile, non-stereospecific formations of the corresponding tetrahydrothiophenes are described. i- s This result is interpreted in terms of a stepwise reaction mechanism with a zwitterion as the key intermediate. Alternatively, this intermediate can cyclize to form seven-membered ketenimines of type 20. With R = Cp3, this product can be isolated in a crystalline form, whereas in the case of R = CN, stable lactam 21 is obtained only after addition of water (eq 10). 

Irradiation of retinyl palmitate (113) with a 150-W high pressure mercury lamp in the presence of thiobenzophenone (114) gave the 1 1 adduct (115) (Yoshioka er a/., 1968). 

Across C=S bonds Allenes undergo a thermal and a photochemical [2+2] cycloaddition reaction with thioketones to give four-membered ring heterocycles. For example, irradiation of tetramethylallene and thiobenzophenone in benzene affords the [2+2] cycloadduct 246 in 64 % yield. As the result of the thermal reaction the linear adduct 247 was formed in 36 % yield... 

Irradiation of thiobenzophenone with cyclo-octatetraene at A > 340 nm gives a 1,4-adduct (40), but, in contrast, 6,6-diphenylfulvene yields" a 1,1-adduct. The photochemical reaction of o-benzylthiobenzophenone has been examined because of its relevance to the reduction of thiobenzophenone." An intramolecular transfer of hydrogen was postulated to give an enethiol, which could be trapped. It is suggested that the photoreduction of thiobenzophenone involves the initial formation of a radical, PhaCSH. The photochemical behaviour of adamantanethione (41) has also been studied. In the ( ,rr ) state it gives the... 

The dimer of hexafluorothioacetone (217) reacts, as shown in Scheme 8, with mercuric fluoride-potassium fluoride to give the mercuric mercaptide of perfluoropropane-2-thiol in DMF, potassium flucnide promotes the reaction of (217) with alcohols, thiols, thiophenols, and olefins to give products derived from the thioacetone monomer. Reaction with styrene gave the bis-Diels-Alder adducts (218) and (219) thietan (220) is obtained with cyclohexene. Amino-alcohols, o-aminophenol, o-aminothiophenol, and o-phenylenediamine yield 2,2-bis(trifluoromethyl)-l,3-het ocyclic derivatives, e.g. (221). 1,3-Dithietans did not react with Fe2(CO) and were discarded as possible intermediates in the ortho-metallation reactions of thiobenzophenones. The hydrolysis reactions of a 1,3-cyclodisiladithietan and its reaction with o-hydroxymercuribenzoic acid have been investigated. ... 

The photocycloaddition of thiobenzophenone to acrylonitrile at 366 nm is known to give the thietan (130). It has now been shown that the reactive state of the thione under these conditions is the second excited (tt, n ) singlet, and that the 1,3-dithian (131) is an intermediate in this reaction. " In contrast to earlier findings, irradiation at longer wavelengths (>500 nm) has been found also to result in product formation. The heterocyclic compounds (132) and (133) were the main products in the latter photolysis reaction, and their formation was interpreted in terms of an intermediate lowest triplet state of thiobenzophenone. The irradiation of thiobenzophenone in tetramethylethylene solution at -78 C afforded two 1 1 adducts, (134) and (135), respectively. Various thietans were the products in the photocycloaddition reactions of some aromatic thioketones with tetramethylallene, 2,4-dimethylpenta-1,3-diene, dimethyl fumarate, and dimethyl maleate, respectively. The nitrile function has also been found to be susceptible to addition by the excited thione group. Thus several alicyclic and aromatic thioketones, on irradiation in acetonitrile solution, have been converted into N-thioacylketimines (136), probably via an intermediate 1,3-thiazetine (137). Two recent papers by de Mayo and his... 

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