hydrobromination of terminal and internal alkynes with a commercially available solution of hydrogen bromide in acetic acid has been investigated for regio- and stereoselectivesynthesis of bromoalkenes. Under an aerobic atmosphere at room temperature, the reaction of ethynylarenes with a small excess of HBr efficiently gave (2-bromoethenyl)arenes with good to high E-selectivity. (Alk-1-ynyl)arenes, or internal