Dithioacetals, acetolysis

The reactivity of 120 is much less than that of either a normal alkene or a dithioacetal. Attempts to hydrogenolyze (see Section IV,3) or reduce 120 with Raney nickel, to hydrolyze the dithioacetal (see Section IV,1) with mercury(II) chloride (even in the presence of an overwhelming excess of the reagent), and to ozonize the double bond at —78°, produce only the starting material an analytical sample was prepared by extended treatment of the crude product with a concentrated, aqueous, alkaline solution of potassium permanganate at the reflux temperature.20 Acetolysis, ozonolysis, or brominolysis of 120 at room temperature affords diphenyl disulfide, and extended oxidation with hydrogen peroxide in acetone, with peroxypropionic acid, and with peroxyacetic acid, produces benzene-sulfonic acid, methyl phenyl sulfone, and an uncharacterized explosive, respectively the products occur as intractable mixtures, and the yields are invariably low. 

Acetolysis of 19-mesyloxy-4-androstene-3,17-dione-3-thioketal under buffered conditions yields the steroidal 3-eno[3,4-b]dithiane 18 in 73% yield. In the absence of buffer, acetolysis leads exclusively to 19-acetoxy-4-androstene-3,17-dione 3-dithioacetal in 65% yield. Subsequent desulfurization of 18 with Raney nickel affords 5f ,19-cycloandrost-3-en-17-one in 81 % yield.The rearrangement of 3-eno[3,4-6]dithiane constitutes a homoallylic cyclopropanation accompanied by sulfur migration. 

Acetolysis of the diethyl dithioacetals of a nmnber of aldoses has been found to give the aldehydo-aldose peracetates. ... 

Synthesis from o-xylose A construction of the AB ring has also been achieved from D-xylose (Scheme 5). D-Xylose was reacted with ethanethiol followed by treatment with formaldehyde to afford the dithioacetal 35, which underwent partial acetolysis of the... 

Whereas acetolysis (H2SO4, AC2O) of peracetylated D-galactose diethyl dithioa-cetal 3 furnishes product 4, as expected, the unprotected diethyl dithioacetal 5 gave penta-O-acetyl-D-galactofuranose 6 under these conditions. ... 

The isopropylidenation of aldose trimethylene dithioacetals is covered in Chapter 6 and the acetolysis of aldose diethyl dithioacetals in Chapter 7. The C-C-l(C-2 bond cleavage of the a-oxoketene dithioacetal 7 on exposure to mineral acid is referred to in Chapters 13 and 14. The phenylthio precursor 8 of 2-keto-3-deoxy-D-flraZ //io-heptonic acid has been prepared by chain-extension of 2,3 4,5-di-O-cyclohexylidene-D-arabinose with PhSCH2C02Me, followed by de-protection. ... 

A number of examples of sulfur participation by dithioacetals and similar derivatives have been reported. The available examples suggest that such groups are quite efficient. The benzylic chloride (62a) undergoes acetolysis 220 times faster than its para isomer and gives the acetate (62c) as the product. S-5 participation is suggested, and structures (63) or (64) were proposed as intermediates. " When the toluene-p-sulfonate (62b) was... 

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