Diiodine thiophenes

Diiodination with iodine proceeds effectively in the presence of nitric acid, which takes the role of an oxidant [119]. Addition of nitric acid also helped the effective mono-5-iodination of 2-substituted thiophenes. Another useful oxidant for thiophene diiodination is hydrogen peroxide [120]. 

The iodination of thiophene rings attached to a borane has been achieved using only NIS as the iodinating agent (Scheme 7.96) [155], The chemistry was carried out under mild conditions in a mixture of acetic acid and chloroform. The reaction was regioselective for the position adjacent to the sulfur center, and simply stirring at room temperature for a few hours generated moderate yields of the diiodinated compound. 

Grignard coupling can also be used to prepare poly(3-alkylthiophene). 3-substituted thiophene is diiodinated according to the method of Barker et al. [26] in which a 1 1 mixture of HN03 H20 is slowly added to the reactor containing the monomer and finely powdered iodine in dichloromethane. 

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