Dehydrogenation with diphenyl disulfide

Aromatization of cyclohexanones. Cyclohexanones undergo dehydrogenative sulfenylation when treated with diphenyl disulfide in methanolic sodium meth-oxide to give o-phenylthiophenols. One limitation is that only one alkyl group can be present at an a-position. This reaction appears to be unique to cyclohexanones cycloheptanone is converted under these conditions to o-phenylthiocyclohepta-none and o,o -bisphenylthiocycloheptanone. 

Azine approach. 1 -Pyridinimines undergo 1,3-dipolar cycloaddition reactions with thiones. In the reaction between 2-isoquinolinimine and carbon disulfide the mesoionic thiadiazole (716) is formed the formation of (716) involves a secondary dehydrogenation of the initial adduct. With diphenyl thionocarbonate, phenoxy group expulsion is succeeded by cyclization leading to the adduct (717) (62TL387). 

In the classical process a phenylethylamine reacts with a carboxylic acid chloride or anhydride to form an amide, which can be cyclised, with loss of water, to a 3,4-dihydroisoquinoline, then readily dehydrogenated to the isoquinoline using palladium, sulfur, or diphenyl disulfide. Common cyclisation agents are phosphorus pentoxide (P Ojq), phosphorus oxychloride and phosphorus pen-tachloride. The electrophilic intermediate is very probably an imino chloride, or phosphate the former have been isolated and treated with Lewis acids when they are converted into isonitrilium salts, which cyclise efficiently to 3,4-dihy-droisoquinolines. ... 

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