There are several reports on Sonogashira couplings, but most of the reported reactions have employed aryl or alkenyl halides as coupling partners. Therefore, Sonogashira coupling is unsuitable for alkyl loadings, especially tertiary alkyl groups. In this research, we found that a copper catalyst is effective for a reaction between a terminal alkyne and an α-bromocarbonyl compound to form a quaternary carbon having alkynyl group at room temperature. Control experiments revealed that a copper acetylide is a key intermediate.

In this paper, we report efficient cyanation of various peptides containing the α-bromocarbonyl moiety using a Cucatalyzed radical-based methodology employing zinc cyanide as the cyanide source. Mechanistic studies revealed that in situ formed CuCN was a key intermediate during the catalytic cycle. Our method could be useful for the synthesis of modified peptides containing quaternary carbons.