Replacement of Halogeno Substituents by Cyano, Sulfo, and Silyl Groups

Replacement of Halogeno Substituents by Cyano, Sulfo, and Silyl Groups 

Displacement of the chloro substituent from pyrazines by the cyano group has not been satisfactorily accomplished (866), but many cyanopyrazines have been prepared from the bromo analogues. Karmas and Spoerri (866) prepared 11 cyanopyrazines with mono-, di-, or trialkyl or phenyl substituents from the corresponding bromo compounds and cuprous cyanide in refluxing dry 4-picoline, but the procedure was not suitable for the preparation of 2-cyanopyrazine (866). It was prepared in 29% yield when the reaction was performed in pyridine (866). Another preparation of 2-cyano-3-phenylpyrazine from the bromo analogue has also been reported (1024). 

2-Fluoropyrazine refluxed with aqueous sodium sulfite for 2 hours gave the sodium salt of 2-sulfopyrazine (ca. 70%) (882,884), whereas 2-chloropyrazine with aqueous sodium sulfite at 150° for 12 hours gave only 44% of the desired product (819, 884). 2-Chloro-3-methylpyrazine (71) with magnesium (and a little methyl iodide) in tetrahydrofuran with phenyldimethylchlorosilane (72) gave 2-methyl-3-dimethylphenylsilylpyrazine (73) (929). 

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