Pyridyl hydrogen sulphide

Substituted 2,3-DAP heated at reflux with a mixture of DMF and DMA furnished 3-(3- dimethylaminoethylindolyl-5)-IP in 63% yield (95MI8). The fusion of an equimolar mixture of pyridine thioamide and 2,3- or 3,4-DAP at 290 °C provided 2-(pyridinyl-2)-IPs (yields not mentioned) (78MI4). Successful results were obtained when stoichiometric amounts of DAP 29,30 and 31 and picolinic acid thioanilide 32 were heated at 155-210 °C (89KG940). The formation of 2-(pyridyl-2)-IPs 43-45 was accompanied by hydrogen sulphide and aniline Uberation. 

The mechanism is likely to include the formation of an intermediate thioamide belonging to Wilgerodt-Kindler s type, then cyclized into the final 2-hetaryl-IP with simultaneous hydrogen sulphide liberation. These intermediate thioamides were not isolated. However, as mentioned, the fusion of o-DAP 29 with picoline-2-thiocarboxylic acid anilide (42) easily afforded 2-pyridyl-IP (43) in a high yield, giving also aniline as a by-product (89KG940). 

Useful products are also obtained by oxidizing alkyl and aryl pyridyl sulphides. With hydrogen peroxide, 2-methylthiopyridine and 6-methyl-thionicotinamide give the sulphoxides, and perbenzoic acid produces the sulphoxide from 2-benzylthiopyridine <. Hydrolysis of the dibromide from 2-pyridyl sulphide gives the sulphoxide" . More commonly the oxidation of... 

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