Diphenyl dithioacetal preparation

Horton and coworkers have described an enol thioacetal-forming, elimination procedure starting from 2,3 4,5-di-0-isopropylidene-n-xylose diphenyl dithioacetal (246) leading to 2-deoxy-4,5-0-isopropylidene-D-tfireo-pent-l-enose diphenyl dithioacetal (247), which is, formally, a carbohydrate ketene derivative. Compound 247, obtained in a yield of 62%, is of potential interest for the preparation of various rare sugars. Treatment with acid converts it into derivatives of heteroaromatic compounds (furans and pyrans). 

Acetalization. Cyclic acetals of pyruvic acid are not easily prepared by using commonly available acetalization methods. Cyclic pyruvic acid acetals of carbohydrates were prepared by DMTST-promoted transacetalization reaction between methyl pyruvate diphenyl dithioacetal and carbohydrate... 

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. 

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