S- thioacetate

Dione-lip-hydroxypregn-4-ene-21-thioacetate-17-butyrate (or hydrocortisone) 10.0 g (0.129 mole) of S-thioacetic acid and 220 ml of hexametapol are introduced into a reactor 27.7 ml of a 4.65 N sodium methylate methanolic solution (0.129 mole) are introduced, accompanied by stirring, at a temperature close to 20°C and then the beige solution is stirred for 1 hour at ambient temperature. Within 10 minutes, a solution of 44.0 g (0.086 mole) of cortisol-21-mesylate-17-butyrate is introduced into 440 ml of hexametapol. The solution is stirred for 2.5 hours at ambient temperature. 

A mechanism of deprotection of 5,S -thioacetals under non-aqueous reaction conditions has been suggested in which oxygen of Mn02 acts as a nucleophilic species (Scheme 1.38). 

A similar mechanism has also been proposed for deprotection of S,S -thioacetals using seleninic anhydride/ ... 

Mikolajczyk, M.. Grzejszczak, S., Zatorski, A., Mlotkowska, B., Gross, H., and Costisella, B., Orga-nosulphur compounds. Part 18. A new and general synthesis of ketene S,S- and O,S-thioacetals based on the Homer-Wittig reaction. Tetrahedron. 34. 3081, 1978. 

The (S)-thioacetate was obtained from the (/ )-alcohol in good yield and with clean inversion of configuration, and smoothly reduced to the (S)-mercaptan (2). 

Related Systems. The carbanions of related 5,5-thioacetals of formylphosphonates also react with aldehydes and ketones, including Q ,/3-unsaturated aldehydes and ketones, to give the corresponding ketene 5,S-thioacetals (e.g. eq 5 ). Horner-Wadsworth-Emmons reactions of carbonyl compounds with 0,S-thioacetals of formylphosphonates [e.g. (Me0)2P(0)CH-(SMe)0Me] and mono(thio)phosphonates [e.g. (Me0)2P(0)-CH2SMe] are also known. 

Conversion of the mesylate 17 to 2(S)-mercapto-Y-butyrolactone (19) was accomplished in a two step process. Displacement of (R)-mesylate with potassium thioacetate in toluene cleanly afforded the (S)-thioacetate 18, which was not isolated, but cleaved to the thiol by treatment with MeOH and anhydrous HCl. Distillation then afforded 2(S)-mercapto-v-butyrolactone (19) in 70% overall yield and >97%ee. 

The synthesis of 11-oxaprostaglandlns from o-glucose uses the typical reactions of gl cofuranose diacetonide outlined on p. 267. Reduction of the hemiacetal group is achieved a thioacetal. The carbon chains are introduced by Wittig reactions on the aldehyde grou] which are liberated by periodate oxidation and laaone reduction (S. Hanessian, 1979 G Lourens, 1975). 

The hetero Diels-Alder [4+2] cycloaddition (HDA reaction) is a very efficient methodology to perform pyrimidine-to-pyridine transformations. Normal (NHDA) and Inverse (IHDA) cycloaddition reactions, intramolecular as well as intermolecular, are reported, although the IHDA cycloadditions are more frequently observed. The NHDA reactions require an electron-rich heterocycle, which reacts with an electron-poor dienophile, while in the IHDA cycloadditions a n-electron-deficient heterocycle reacts with electron-rich dienophiles, such as 0,0- and 0,S-ketene acetals, S,S-ketene thioacetals, N,N-ketene acetals, enamines, enol ethers, ynamines, etc. 

The most common procedure previously employed to effect the elimination of thiols from thioacetals has been heating in the presence of a protic acid. For example, propionaldehyde diethyl thioacetal is converted to 1-ethylthio-l-propene on heating at 175° in the presence of phosphoric acid. The relatively high temperature and acidic conditions of such procedures are, however, distinct disadvantages of this method. Another approach consists of oxidation of a thioacetal to the mono S-oxide and thermal elimination of a sulfenic acid at 140-150°. ... 

The "smelly shoe" of the elements. The oxidation product S02 has an acrid, burning smell, the reduction product H2S stinks like rotten eggs and is very toxic. Sulfur is, nevertheless, a most useful element. It occurs in elemental form and has therefore been known for a long time is mentioned in the Old Testament. Its main application today is in the production of fertilizers. Considerable amounts of sulfur are used in tire production for vulcanization. Sulfur is also a component of gunpowder. Physiologically indispensable as thioacetic acid and especially the S-S bridges that fix proteins in their shapes (e.g. insulin, but also in perms). A 70-kg human being contains 140 g of sulfur. 

C. Moreau, J. Lecomte, S. Mseddi, and N. Zmimita, Stereoelectronic effects in hydrolysis and hydrogenolysis of acetals and thioacetals in the presence of heterogeneous catalysts, J. Mol. Catal. A Chem., 125 (1997) 143-149. 

In addition to bacterial conversion of L-methionine to cheese aroma compounds, certain cheese-ripening yeasts have been implicated. They include De-baromyces hansenii, Geotrichum candidum, and Yarrowia lipolytica, in addition to Kluyveromyces lactis and Saccharomyces cerevisiae (previously noted). Of these yeasts, Geotrichum candidum was most effective at producing sulfur compounds with the major product being S-methyl thioacetate, with smaller amounts of MT, DMS, DMDS, and DMTS. Kluyveromyces lactis had a similar profile, but produced a much smaller amount of S-methyl thioacetate than did G. candidum. S-Methyl thioacetate is formed by a reaction of MT and acetyl-CoA (Equation 7) ... 

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