1.2- Dicarbonyl compounds from 1,3-dithianes

Oxidative hydrolysis of 1,3-dithianes using N-halosuccinimides has been extensively investigated . The yields were consistently high when using N-bromosucdnimide (NBS), usually in acetonitrile. Unlike earlier methods 2-acyl-1,3-dithianes were efficiently hydrolysed to 1,2-dicarbonyl compounds. For example, 1-phenyl-1,2-propanedione was prepared in quantitative yield from the 2-benzoyl-2-methyl-l,3-dithiane (equation 14). Silver salts often aid the reaction, but it has been noted that NBS in the... 

Some of the problems associated with the synthesis of a-dicarbonyl starting materials have been alleviated by the use of propane-1,3-dithiol, which reacts with aldehydes to give cyclic thioacetals. With butyllithium the resulting stable dithiane anions (134) can be transformed into a-diketones or a-hydroxy ketones (Scheme 73). A further approach to such compounds is found in the reaction of a-ketonitrate esters with sodium acetate (Scheme 73), while aryl a-diketones are also available from a-ketoanils (prepared from the cyanide-ion-catalyzed transformation of aromatic aldimines) (70AHC(12)103). 

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