Thioketones thiophilic addition

As mentioned before, it was with thioketones that the first cases of thiophilic addition were evidenced, but many other modes of reaction have been observed concurrently carbophilic addition, reduction, coupling, double addition, and enethiolization [357]. We will not discuss these reactions here, which have not been used much for synthetic purposes. 

Rule 3 correctly predicts the experimentally observed thiophilic addition. Simple thio-aldehydes and thioketones always have a greater LUMO coefficient at C than S. The results are opposite here and this reversal reflects the experimental results nicely. 

Allyl silanes may also be employed for thiophilic addition to various sulfines, obtained by oxidation of thioketones, dithioesters [151] and trithio-carbonates [111]. It provides a new entry to allyl sulfoxides. 

Thioketones markedly differ from ketones in their reactions with electrophilic reagents.1,4 Ketones react chiefly at the a-carbon atom, whereas with thioketones the electrophile preferentially attacks the sulfur atom (thiophilic addition), leading to derivatives of the enethiol. The reactions are often performed in the presence of a base (Scheme 15). Thus, alkylation and acylation yield the enethiol derivatives (24) and (25). Similarly, reactions with an arenesulfenyl chloride, with carbon disulfide followed by an alkyl iodide, and with a carbonyl compound afford the compounds (26), (27) and (28), respectively (Scheme 15). The mechanisms of formation of the last two products are depicted in Scheme 16. 

While thiones give sulphides through thiophilic addition of alkyl- or aryl-lithiums (see also Chapter 3, p. 131), di-t-butyl thioketone reacts through an alternative reaction path (Scheme 1), leading to hindered thiols. jS-Phenylethyl... 

Reactions of different organometallic species with thiocarbonyi compounds have been extensively investigated and been shown to proceed both in a carbophilic and a thiophilic fashion. However, other reactions can be observed simultaneously such as reduction, double addition, coupling, deprotonation and formation of enesulfides1,226,423. A complex pattern appears in the reactions of thioketones with lithium or Grignard reagents424. The first application of Reformatsky reagents in C—C bond formation by reaction with... 

A new class of nucleophiles have been introduced for sulfur addition. Degl Innocenti and his group [145, 146] have shown that allyl or benzylsi-lanes, in the presence of tetra-n-butylammonium fluoride, reacted in a thiophilic fashion and led to allyl sulfides or dithioacetals. It is remarkable that this selective reaction is general for a large variety of thiocarbonyl compounds thioketones [145], dithioesters [146], and even with the normally sluggish trithiocarbonates [145]. With substituted allyl silanes retention of configuration of the allyl chain is observed. It is noteworthy that the possible [2,3] sigmatropic shift of the intermediate anionic species was not observed. 

On the whole, reactions of thioketones with vinyl-, allyl-, propargyl-, benzyl-, and, sometimes, methylmagnesium halides proceed by carbophilic addition [1-3] (though subsequent rearrangements to the thiophilic product may occur [2]) ... 

Only a few studies have been made on this reaction. Saturated Grignard reagents react with a, -ethylenic thioketones [28,29] to lead to a mixture of several products. They principally result from thiophilic 1,2-addition, thiophilic 1,4-addition, and 5-alkylation [28,29]. 

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