Details

Autor(en) / Beteiligte

• Boese, R.
• Harvey, D.F.
• Malaska, M.J.
• Vollhardt, K.P.C.

Titel

2 + 2 + 2Cycloadditions of alkynes to furans and thiophenes. A cobalt-mediated [open quotesenol ether walk[close quotes

Ist Teil von

• Journal of the American Chemical Society, 1994-11, Vol.116:24

Ort / Verlag

United States

Erscheinungsjahr

1994

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Involvement of the 2,3-double bond of furan and thiophene in cycloadditions is relatively uncommon, usually limited to specific substrates or by special conditions. Our finding that indoles, pyrroles, imidazoles, and uracils can be activated by CpCo to undergo cocyclizations with alkynes suggested an extension of these efforts to the title heterocycles, in particular because the latter constitute new brackets for the degree of aromaticity (furan lowest, thiophene highest) that is subject to neutralization in these reactions and because the anticipated enol (thio)ether products exhibit potential synthetic utility. This study demonstrates that the cobalt-mediated [2 + 2 + 2] methodology can be extended to furans and thiophenes but that in these, and possibly generally in related heteroalkenes, the generation of potential dienylic leaving groups in the resulting CpCo diene product may cause rearrangements and that formal C-H activations may complicate the outcome of the reaction. The observation that the relatively highly aromatic thiophene nucleus functions as a cocyclization partner points the way to a number of even more challenging substrates in this process. 20 refs.