Thiobenzaldehydes

Historically, this represents the first thiophene synthesis, when Laurent obtained tetraphenylthiophene by heating polymeric thiobenzaldehyde in 1844. Almost any aromatic methyl derivative can be converted to tetraphenylthiophene, which is thermodynamically the most stable thiophene, by heating with sulfur. Toluene, phenylacetic acid, benzyl alcohol, benzyl sulfide or disulfide, benzyl sulfonate or even sodium thiobenzoate have been converted to tetraphenylthiophene under these conditions (52HC(3)l). 

Another route to thioaldehyde and thioketone complexes uses the tungstate [W(CO)5SH] as the precursor. When [W(CO)5SH] was treated with ketones in the presence of trifluoroacetic acid, thioketone complexes [W(CO)5 S = C(R1)R2 ] were formed. Analogously, thiobenzaldehyde complexes were obtained from [W(CO)sSH]- and benzaldehydes bearing electron-releasing para substituents. Benzaldehyde, benzaldehydes with electron-withdrawing substituents, and aliphatic aldehydes did not react. Presumably, the binuclear dianion [p,-S W(CO)5 2]2 is an intermediate in the reaction, as on acidification of a mixture of [ju,-S W(CO)5 2]2 and p-N, A -dimethylaminobenzaldehyde the thioaldehyde complex [W(CO)5 S = C(C6H4NMe2-p)H ] is formed.143... 

In contrast to 51a but analogous to [W(CO)5 S = C(Ph)H ] (99a), the cationic thiobenzaldehyde ruthenium complexes 78 [see Eq. (16)] added PMe3 to give phosphoniothiolato complexes. 47 Complexes 78 also reacted... 

Three-membered rings should in principle be accessible by reaction of heteroaldehyde and -ketone complexes with Q sources. This was verified by the synthesis of the thiirane complex 143 from thiobenzaldehyde complex 99a and diphenyl diazomethane [Eq. (30)]. The reaction was assumed to proceed via a 1,3,4-thiadiazolidine complex as the intermediate that loses dinitrogen to give 143.254... 

This "thiophilic" mode of reaction fits well with the other ionic and radical thiophilic additions on a thiocarbonyl group (see [120], and the Barton-McCombie radical thiophilic addition [227] previously discussed in Sections 4.2.2 and 3.2). With thioaldehydes, both C-C and C-S bonds were formed, as in the following case in which 0-pinene was used to trap thiobenzaldehyde [514] ... 

An interesting reaction has been reported by Glass and coworkers344 consisting of the attack of a selenium heterocycle, Ebselen oxide 66, by a-toluenethiol (equation 69). In this reaction thiobenzaldehyde has been invoked as intermediate and could be trapped with cyclopentadiene. In the absence of a diene, dibenzyl disulfide is isolated instead of... 

More attention has been paid to tungsten complexes and Raubenheimer and coworkers502 studied the reactions of carbene complexes such as [W(CO)s C(OEt)Ph) with a variety of electrophiles to give coordinated thioaldehydes. Fischer s group has reported many studies on the behavior of pentacarbonyltungsten-coordinated thiobenzaldehyde [(CO)sW S=C(Ph)H ] with vinyl ethers503 (equation 153) and alkynes504. 

Only one isolated example of formation of thioketene and thioaldehyde dimolybdenum complexes has been reported507, but in contrast, zirconocene thioacetaldehyde and thiobenzaldehyde complexes, introduced by Buchwald, have been the subject of several studies508, including their application in the synthesis of novel antimony thiametallacy-cles 148509 (equation 156). Compound 146 was generated in situ and, after reaction with alkynes, gave rise to metallacycles 147 which, by treatment with SbCR, afforded 148. 

Thiobenzaldehydes. The first stable thiobenzaldehyde, 2,4,6-tri-f-butylthio-benzaldehyde (2), has been prepared by oxidative sulfuration of the hydrazone 1 with Sj( j... It has also been prepared by treatment of 2,4,6-lri-r-butylphenyllithium (3)... 

Nevertheless, if the cyclization of the succinonitrile with this acid is carried out in the presence of thiolacetic acid, 2-imino-5-thioxo-pyrrolidine hydrohalides (121) are obtained in good yield.98 These compounds very readily convert benzaldehyde to thiobenzaldehyde trimer. 

C-Substituted octathionane 15b, when reacted with 7 equiv of triphenylphosphine, desulfurized to produce the corresponding 2,4,6-trisubstituted thiobenzaldehyde <1997CEJ62, 1994PS389>. Partial desulfurization to pen-tathiane 84 occurred when 3 equiv of PPh3 was used (Scheme 14) <1994PS389> (Chapter 9.14). 

Reaction of thiobenzaldehyde-anthracene cycloadduct 385 with 2-methoxyfuran in toluene at 90 °C for 3 h gave thiirane 386 (mixture of (E)- and (Z)- isomers) and methyl 2-(Z)-penta-2,4-dienoate 387 (Equation 59) <2003TL1179>. 

In 1841, Laurent obtained thiobenzaldehyde decamer from reacting oil of bitter almonds (which is mostly benzaldehyde) with ammonium sulfate (1841LA320), although the size of the oligomer was not established until... 

Thiobenzaldehyde trimer, (CgHjCHS), is decomposed at 230° by freshly reduced copper powder to give stilbene, CgHjCH—CHCgH, (45%). Several benzologs and alkoxyl derivatives of stilbene have been prepared by this method in low yields. The trimers of the thioaldehydes are readily prepared from their oxy analogs, hydrochloric acid, and hydrogen sulfide. 

The photoreactions of the stable thiobenzaldehyde (104) have been de-scribed. " Thus cycloaddition of (104) to allenes gives the thietanes (105) in... 

The photocycloaddition of thiocarbonyl-containing compounds to alkenes provides an easy route to thietanes. 2,4,6-Tri-(t-butyl)thiobenzaldehyde (249) undergoes regiospecific addition to substituted allenes (250) to give the vinyl-thietanes (251). The formation of the ketones (252) by irradiation of the aryl... 

The case of thiobenzaldehyde dianions, which are available from benzylthiol and two equivalents of n-butyllithium-TMEDA complex, merits further comment since alkylation or allylation of these species occurs selectively at the carbanionic site and then a second alkylation can be carried out on the thiolate group (Scheme 16, entry a). ... 

Electron-deficient thiocarbonyl compounds such as hexafluorothioacetone, metfiyl cyanodithiofor-mate " and thioglyoxylate esters are particularly reactive enophiles. Since these compounds react primarily or exclusively by pathway (b) to give allylic sulfides (264), rather than by pathway (a) to give homoallylic thiols (263), they are outside the scope of this chapter (Scheme 39). Thiobenzaldehyde, generated in situ, reacts with (3-pinene to give thiol in 38% yield and sulfide in 19% yield. ... 

Addition of thiobenzaldehyde to 9,10-dimethylanthracene gave a [4 + 2] cycloadduct, which on heating in the presence of another diene gave a new dihydrothiapyran, again via a facile retro-Diels-Alder reaction.18-21... 

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