Oxidative Cleavage of β-Keto Sulfones via Nitrous Acid

The reaction of nitrous acid with 1-aryl-2-(arylsulfonyl)ethanones 3a-e afforded the unexpected arenecarboxylic acids 12a-e, formic acid 14, and benzene/4-toluenesulfinic acid 15a, b through oxidative cleavage reaction. 4-Chlorobenzoic acid (12a), [ 1,1'-biphenyl]-4-carboxylic acid (12b), 2-naphthoic acid (12c), 2-thiophenecarboxylic acid (12d), and 2-benzofurancarboxylic acid (12e) were isolated in 72%, 62%, 55%, 58%, and 62% yields, respectively. The reported mechanistic pathways proposed the production of 1-aryl-2-(phenyl/tolylsulfonyl) ethane-1,2-dione 7 instead of arenecarboxylic acids 12. A mechanistic pathway to explain the reaction of nitrous acid with 1-aryl-2-(arylsulfonyl) ethanones 3a-e was suggested. In this pathway, the intermediate 1,2-oxazete 10 lost benzene/4-toluenesulfinic acid 15 to produce 1,2-oxazet-3-one 11. Ring cleavage of the latter intermediate afforded the arenecarboxylic acids 12.