Regio- and stereoselective synthesis of bromoalkenes by homolytic hydrobromination of alkynes with hydrogen bromide

• Published in: Tetrahedron Vol. 110; pp. 132687 - 132696
• Main Authors: Kumaki, Wataru, Kinoshita, Hidenori, Miura, Katsukiyo
• Format: Journal Article
• Language: English
• Published: OXFORD Elsevier Ltd 26.03.2022; Elsevier
• Subjects: Alkyne; Bromoalkene; Chemistry; Chemistry, Organic; Hydrobromination; Physical Sciences; Radical addition; Science & Technology; Bromoalkene; Hydrobromination; Radical addition; Alkyne; HALIDES; ACIDS; TERMINAL ALKYNES; CROSS-COUPLING REACTIONS; ELECTROPHILIC ADDITION; CIS-TRANS ISOMERIZATION; ANTI-MARKOVNIKOV HYDROBROMINATION; VINYL BROMIDES; METAL-FREE; MICROWAVE-INDUCED REACTION
• ISSN: 0040-4020; 1464-5416
• DOI: 10.1016/j.tet.2022.132687

Homolytic hydrobromination of terminal and internal alkynes with a commercially available solution of hydrogen bromide in acetic acid has been investigated for regio- and stereoselective synthesis 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 alkynes bearing both phenyl and alkyl groups at the sp-carbons also underwent the air-initiated hydrobromination to exhibit high Z-selectivity under kinetic conditions using a half equivalent of HBr. [Display omitted] •Regio- and stereoselective direct hydrobromination of terminal and internal alkynes.•A cost-effective, atom economical and simple method for preparing bromoalkenes.•Successful kinetic and thermodynamic control for stereoselective homolytic hydrobromination.