Chloro ketones with silver

Treatment of a-chloro sulfones 250 with silver perchlorate in refluxing trifluoroacetic acid containing a small amount of water gives the corresponding aromatic ketones 251 in good yields (equation 150)143. 

The highest yields for this reaction were obtained with an unsubstituted amide and with one containing a p-chloro substituent, with vinyl methyl ketone as the alkene. Use of styrene led to lower yields. The reaction of the intermediate aceta-nilidopalladacycle with methyl iodide, which produces N-o-tolylacetamide is interesting mechanistically [7b], Stoichiometrically, full conversion was achieved, but attempts with catalysts gave only 10 turnovers and required the use of silver acetate to convert palladium iodide into the acetate, because palladium iodide does not have enough activity for metalation. 

The same allylic alcohols (142) undergo regiospecific oxidative cleavage with pyridinium chloro-chromate at the ethylenic bond to give, after saponification, a-hydroxyacids (145). Extension of this reaction to a -unsaturated ketones (146), obtained by oxidation of secondary alcohols with silver carbonate on celite, affords a-ketoacids (147) <88TL626l>. 

Silver salts are also utilized to perform nucleophilic additions to disulfide bonds to yield sulfenamides (146). If alkyl halides are treated with stoichiometric AgBF4 in dimethyl sulfoxide solvent (DMSO, solvent), the corresponding aldehydes/ ketones will form in good yields. This reaction is an alternative to the well-known Swern oxidation (147). In addition, silver can drive the formation of dialkylper-oxonium ions from alkyl halides, which then oxidizes sulfoxides or sulfides (148,149). In the presence of AgN03, sulfides can be oxidized into a-chloro sulfoxides by SO2CI2 (Fig. 36) (150). 

Titanium(iii) chloride and HCl provide a means of reduction of a,a-dibromo-ketones to the corresponding a-chloro-compounds [equation (50)]. ° a,a -Dibromo-ketones are reduced to a-acetoxy-ketones by ultrasonically dispersed mercury in acetic acid. A wide variety of dienes react with a,a -dibromo-ketones in the presence of a zinc-silver couple or an iron carbonyP in the [3 + 4 - 7] sense to give cyclohept-4-enones [equation (51)]. 

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