Sulfur-nitrogen bonds, reductive cleavage

Ketones containing sulfur or nitrogen atoms bound to a-carbons suffer carbon-sulfur or carbon-nitrogen bond cleavage under the conditions of the Clemmensen reduction [159, 864 (p. 118). A ketosulfone was reduced to a sulfone-alcohol with zinc in refluxing 80% acetic acid in 70% yield [920]. 

The nitrogen-sulfur bond in 161 (X = S, R = NPhth X = S02, R = OMe) is easily broken under certain conditions. For instance, attempts to obtain a palladium-catalyzed carbonylation reaction with the iodide gave only the ring-opened disulfide 162 and the sulfonic acid 163, presumably by reductive cleavage of the N-S bond by the triphenylphosphine in the reaction mixture <2000T5571>. 

In A-tosylcarboxamides there would be a competition in the reductive cleavage of the radical anion between the carbon-nitrogen bond and the nitrogen-sulfur bond in DMF containing acetic acid the sulfinate is reductively split off. The yeld of deprotection is highest when a mercury electrode is used [262]. 

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