Gold(I)-catalyzed direct C-H arylation of pyrazine and pyridine with aryl bromides

An efficient procedure for the direct C-H arylation of electron-poor aromatics such as pyrazine and pyridine with aryl bomides is described. In the presence of catalytic amount of Cy3PAuCl and with the use of t-BuOK as base. pyrazine undergoes the direct C-H arylation with aryl bromides at 100 degrees C, and the yields of the arylated products depend on the nature of aryl bromides. in the cases of electron-rich aryl bromides used, the arylated pyrazines can be obtained in good to high yields. For electron-poor aryl bromides, the addition of AgBF4 is the crucial point to accelerate the coupling reaction to give the arylated products in moderate yields. Pyridine also reacts with electron-rich aryl bromides catalyzed by Cy3PAuCl to give a mixture of arylated regioisomers; in moderate yield. However, in order to realize the direct C-H arylation of pyridine with electron-poor aryl bromides, the addition of silver salt as additive and a milder reaction temperature (60 degrees C) are required. (C) 2009 Elsevier Ltd. All rights reserved.