Thioacetal with mercury chloride

On the one hand, thioacetals of a,B-unsaturated ketones resulting from the a-alkylation reaction reported above have been transformed efficiently into the corresponding unsaturated ketones on reaction with mercury(II) chloride and oxide in methanol (Scheme 71, entry or on reaction - with... 

The above reactions in this section have been examples of addition alone or addition followed by elimination. Ligand reactions involving nucleophilic substitution are also known and these are of the dealkylation type. Lewis acids such as aluminum chloride or tin(IV) chloride have been used for many years in the selective demethylation of aromatic methyl ethers, where chelation is involved (Scheme 27). Similar cleavage of thioethers, specially using mercury(II) salts, is commonly used to remove thioacetal functions masking ketones (equation 27).104 In some cases, reactions of metal ions with thioether ligands result in isolation of complexes of the dealkylated organic moiety (equations 28 and 29).105-107... 

Dithiolanes are quite resistant to both alkaline and acid hydrolysis, however the ring can be cleaved by cadmium carbonate and mercury(II) chloride, a well-known reagent for hydrolyzing thioacetals (53MI43200). Thus the 1,3-dithiolane derivative (218) is hydrolyzed by this reagent with formation of the hydroxydithiol (219). A similar reaction takes place on reduction of the 1,3-dithiolane derivative (218) with sodium and ethanol in liquid ammonia to produce the hydroxydithiol (219) (47JCS592). 

Although 1,2-dicarbonyl substrates (especially unsymmetrical benzils) are often difficult to make, there are a number of approaches which may be appropriate. Propane-1,3-dithiol reacts with aldehydes to give cyclic thioacetals (in 52-91% yields) which form stable dithiane anions when treated with butyllithium. Subsequent quenching with an acid chloride followed by mercury(ll) chloride treatment gives a 1,2-dicarbonyl species. Alternatively, substitution of an aldehyde for the acid chloride gives rise eventually to an a-hydroxycarbonyl derivative (Scheme 5.1.2) [16j. An alternative approach to a-ketoaldehydes (82-86% yields) reacts an a-ketonitrate ester with sodium acetate in DMSO [17]. Aryl a-diketones can be made from a-ketoanils, which are in turn made by cyanide ion-catalysed transformation of aromatic aldimines [18], and the range of unsymmetrical benzils has been increased by... 

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