A new approach to the synthesis of 2-vinylthiophenes and selenophenes; competition between free radical and anionic cycloaromatization of bridged di- and tetrapropargylic sulfides and selenides

• Published in: Tetrahedron Vol. 59; no. 15; pp. 2641 - 2649
• Main Authors: Zafrani, Yossi, Cherkinsky, Marina, Gottlieb, Hugo E, Braverman, Samuel
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 07-04-2003
• Subjects: acetylenes; allenes; anionic cyclizations; radical cyclization; sulfur and selenium heterocycles; allenes; radical cyclization; acetylenes; anionic cyclizations; sulfur and selenium heterocycles
• ISSN: 0040-4020; 1464-5416
• DOI: 10.1016/S0040-4020(03)00327-2

A series of unknown di- and tetrapropargylic sulfides and selenides have been prepared. In the presence of
t-BuOK in dry THF these compounds underwent isomerization to the corresponding diallenes, followed by a tandem anionic cyclization and aromatization to 2-vinylthiophene or selenophene derivatives. Some mechanistic studies indicated competition between free radical and anionic cycloaromatization. The latter is influenced by the nature of the bridging heteroatom, substitution of the allenyl group and base concentration.
Graphic