Dehalogenation heterocyclic halides

The removal of a halogen from an aromatic heterocycle takes place more readily than the hydrogenolysis of a phenyl halide of the same type (Eqn. 20.61). 45 The relative difference between the ease of dehalogenation of a phenyl and a heterocyclic halide is more pronounced over Raney nickel in basic medium than it is over palladium (Eqn. 20.62). 46... 

Hydrolysis of esters and ethers, hydrolytic cleavage of C—N single bonds, hydrolytic cleavage of nonaromatic heterocycles, hydration and dehydration at m ultiple bonds, new atomic linkages resulting from dehydration reactions, hydrolytic dehalogenation removal of hydrogen halide molecules, various reactions. 

Some heterocyclic aryl halides are very likely to dehalogenate. In the case of oligothiophenes, the halogenation was highly dependent on small changes of the electronic structure of the aryl halide [87]. The side reaction was suppressed by adjusting the basicity of the reaction mixture. In other cases an alternative StiUe protocol was found [88]. 

Dicyanopropenes provide a valuable source for ring-closure reactions and have been used in a variety of syntheses of N-heterocycles. When a,j -unsaturated esters 424 reacted with 10, pyridones 425 were obtained and were in turn converted into dinitrile 426 with cyanamide. 426 was cyclized by hydrogen halides and yielded products 427 and 428 (X = Cl, Br, I). Dehalogenation afforded 429 and 430 Ionic species like 431 or... 

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