Ketones mercaptals, cyclic

Mercuric acetate Ketones from cyclic mercaptals... 

Hydrocarbons from alcohols via bromides s. 18, 125 Replacement of hydroxyl by hydrogen via mesylates and iodides s. 19, 114 via mesylates and benzyl thioethers s. 16, 107 via ketones and cyclic mercaptals s. 16, 138 OH H... 

Thioketals are readily formed by acid-catalyzed reaction with ethane-dithiol. Selective thioketal formation is achieved at C-3 in the presence of a 6-ketone by carrying out the boron trifluoride catalyzed reaction in diluted medium. Selective protection of the 3-carbonyl group as a thioketal has been effected in high yield with A" -3,17-diketones, A" -3,20-diketones and A" -3,l 1,17-triones in acetic acid at room temperature in the presence of p-toluenesulfonic acid. In the case of thioketals the double bond remains in the 4,5-position. This result is attributed to the greater nucleophilicity of sulfur as compared to oxygen, which promotes closure of intermediate (66) to the protonated cyclic mercaptal (67) rather than elimination to the 3,5-diene [cf. ketal (70) via intermediates (68) and (69)]." " ... 

Methyl glyoxylate diethyl mercaptal added at 4° to a soln. of NaH in dimethoxy-ethane, stirred 40 min., then methyl vinyl ketone added product. Y 93%. F. e. s. J. L. Herrmann, R. H. Schlessinger et al., Tetrah. Let. 1973, 2595 with cyclic mercaptals cf. ibid. 1973, 2599. ... 

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