Thiophile, basic

DHPM 22 has been transformed to 2-(2-hydroxy-2-arylvinyl) dihydropyrimidine derivatives 90 via Eschenmoser sulfide contraction through the selective alkylation of 22 at C-2 with a-bromoketone 88 under basic conditions and subsequent elimination of the bridged sulfur by the thiophilic... 

Owing to the lability of the interflavanyl bond in procyanidins under either acidic or basic conditions, the existing semi-synthetic methods (28, 29) invariably result in an equilibrium between substrates and products. Such a labile bond and the apparent preference of the electrophile for the di- and trimeric products (see Scheme 1), once condensation is initiated, furthermore give poor control over the level of oligomerization. We thus assessed (52) the effectiveness of the thiophilic Lewis acids, dimethyl(methylthio)sulfonium tetrafluoroborate (DMTSF) (55, 54) and silver tetrafluoroborate (AgBF4)(55) to activate the C(4)-S bond in the 4-thioethers of flavan-3-ols towards carbon nucleophiles and hence to generate the interflavanyl bond of procyanidins under neutral conditions. 

Ketones from thiolic acid esters. - -Di-ketones. A soln. of the startg. thioester and LiBr in anhydrous acetonitrile treated with bis - (3 - dimethylaminopropyl) phenyl-phosphine, a basic thiophile, stirred and heated 17 hrs. at 70° product. 

The STaz moiety was found stable toward common protecting group manipulations involving basic and acidic conditions, for example, acetylation, benzylation, acetal formation and cleavage, etc. (77). The STaz derivatives were found to be stable toward hydrolysis in the presence of acidic thiophilic reagents. Thus, comparative hydrolytic stability studies showed that STaz glycosides are even more stable than their 1-5-ethyl and 1-5-phenyl counterparts in the presence ofNBSorNlS/TfOH. 

It is most profitable to ask the question whether the parallelism between an Sn2 on carbon and on sulfur is at all general. In fact one must ask a more basic question concerning what controls the nucleophilic or thiophilic behavior of some reagent. Foss (1950) forms three categories of displacing reagents on the sulfur bond ... 

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