Treatment of bis(1-phenylethynyl)-phenylstibine with 2,4,6-trimethyl magnesium bromide promotes the nucleophilic displacement of one ethynyl group, as was previously reported by Kurita, affording the phenyl (1-phenylethynyl)mesitylstibine. This antimony compound was used as a ligand in order to modify the Co-2(CO)(8) catalytic system for the amidocarbonylation (Wakamatsu reaction) of cyclohexene, cyclopentene, 1-hexene, and 1-pentene. This new modified catalytic system is capable of affording moderate yields of N-acetyl-a-aminoacids. (c) 2007 Elsevier B.V. All rights reserved.