Reactions with thiobenzophenone

Reaction with thiobenzophenones. Treatment of thiobenzophenones (1) with diiron nonacarbonyl in benzene at 25° gives orilio-metalated complexes (2) in reasonable to high yield. The purple-red complexes are stable to air. One... 

Though normally, Diels-Alder reactions of 3,4-di-tert-butylthiophene 1-oxide and related compounds occur exclusively at the syn-n-face, exceptions have also been observed. For example, in its reaction with thiobenzophenone, two diastereo-mers 50 and 51 were obtained. The major diastereomer 50 was isolated in 76% yield, but the minor diastereomer 51 was also produced, in 15% yield, the conformation of which was established by X-ray diffraction analysis (Scheme 46). This example reveals that the reaction takes place predominantly at the syn-jr-face to the S=0 bond, though not exclusively. The jr-face selectivity was explained in terms of the extent of conformational changes of 3,4-di-[Pg.248]

In contrast, several At-arylketenimines undergo the [4+2] cycloaddition reaction with thiobenzophenone to give 3,1-benzothiazines 71 in high yields. 

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. 

Reaction of thiobenzophenone with chloromethyl methyl sulphoxide 412 does not give the expected 2,2-diphenyl-3-methylsulphinylthiirane 417, but the a, /1-unsaturated sulphoxide 418 in a 38% yield485 (equation 248). 

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... 

In the reactions which we have just discussed, the initial reaction involves only the carbonyl group. We therefore looked next at reactions of tetrachlorobenzyne with simpler aldehydes. It is noteworthy that o-carboxybenzenediazonium salts are known to yield 1,3-benzodioxan-4-ones, for example, (129) with carbonyl compounds 166>, and 2,2-diphenyl-3,l-benzo-oxathian-4-one (130) with thiobenzophenone 167>. These products are presumably formed via reactions with the intermediate (128). 

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. 

Over the past two decades, important contributions to the chemistry of thiocarbonyl ylides were made by Huisgen et al. (27). By carrying out the reaction of thiobenzophenone with diazomethane at low temperature, formation of 2,5-dihydro-l,3,4-thiadiazole (15) with subsequent elimination of N2 was established as the route to the reactive thiobenzophenone (S)-methylide (16) (17,28). In the absence of intercepting reagents, 16 undergoes electrocyclization to give 17 or head-to-head dimerization to yield 1,4-dithiane 18 (Scheme 5.3). 

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. 

V-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 ... 

The 2-silathietane is thought to be formed as an intermediate in the reaction of 1,1-dimethylsilacyclobutane with thiobenzophenone, since the cyclodisilthiane and 1,1-di-phenylethene are the products (Scheme 99) (75JOM(101)17l). These products support the... 

The usual synthetic entry into this ring system (6) is by the dehydration of isothiochromanols.274 Compounds 6 are also available via the photochemical reaction of thiobenzophenone with acetylenic compounds.275... 

The reaction of a lanthanide metal, ytterbium, has been explored by the group of Fujiwara [164-166]. Among the various processes (coupling, desul-furisation, etc.) which were evidenced, a nice application was achieved by successive reaction of thiobenzophenone with ytterbium, and treatment of the intermediate with a dihalide. Thiolanes, for instance, were thus obtained in an expedient manner. 

Stereochemical studies have established [206] that the thermal reaction of thiobenzophenones with (Z),( )-2,4-hexadiene leads to dihydro-(2H)-thiapy-rans with cis/tmns ratios usually superior to 98 2. On the other hand, achieving the addition at 12 kbar and ambient temperature (with a special technique to avoid diene isomerisation) provided mixtures in which the trans isomer was predominant. It is remarkable that, with pressure, conservation of the diene geometry with a concerted pathway is observed whereas, at normal pressure, a stepwise mechanism has to be assumed. This unprecedented dichotomy is probably linked to the low reactivity of the cis,trans diene isomer. 

---