Halothio

Gronowitz, S. Bobosik, V. Lawitz, K. Palladium Catalysed Synthesis of Unsymmetrical Bithienyls from Thiopheneboronic Acids and Halothio-phenes, Chemica Scripta 1984, 23, 120-122. 

Molecular halogens react with the thiones to give initially 1 1 adducts, formulated probably as 3-halothio-l,2-dithiolylium halides (42). For chlorine, these types convert to 3-chloro-1,2-dithiolylium salts (35a X = C1) (81AHC(23)i5l, 76PS(i)i85). Other more easily controlled halogen sources may be used, including thionyl chloride, oxalyl chloride, sulfur chloride and phosphorus oxychloride (70LA(742)103). A possible pathway for reaction with oxalyl chloride is shown in Scheme 19. 

The reactions of 1,2-dithiole-3-thiones (2b) with various types of halogen reagents forming 3-halo-l,2-dithiolium cations (29b) <76PS(1)185> can be treated as a nucleophilic attack of a halide ion, or a halogen source on a type of initially formed 3-halothio-1,2-dithiolium salt (69b). 

By analogy with the general synthesis of imidoyl chlorides it can be expected that carbamates and thiocarbamates undergo reaction with a variety of acid halides to afford 1-haloformimidates and 1-halothio-formimidates, respectively. For example, carbamates have been reacted with carbonyl chloride ( ), pyrocatecholphosphorus trichloride ( ), and phosphorus pentachloride ( ), and isocyanates were obtained. In view of the catalytic effect of N,N-dimethylformamide in the phosgenation of carbamates to isocyanates, the intermediacy of 1-chloroformimidates X is anticipated ( ). 

In 1966 Neidlein, Haussmann, and Heukelbach investigated the reaction of thioacetals, XXV with bromine and chlorine, and the authors obtained good yields of the corresponding N-arenesulfonyl-l-halothio-formimidates (XXVI). 

Elimination of alkylhalide from 1-haloformimidates and 1-halothio-formimidates yields isocyanates and isothiocyanates, respectively... 

Mercuration of thiophenes occurs with great ease mercuric acetate is more reactive than the chloride tetrasubstitution and easy substitution of halothio-phenes can also be achieved. ... 

A third approach involves the Kumada procedure, in which the Grignard reagent of a thiophene derivative is coupled with a halothio-phene (Scheme 19). It is probably the most reliable method for making... 

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