[2 + 2 + 2]Cycloadditions of alkynes to furans and thiophenes. A cobalt-mediated [open quotes]enol ether walk[close quotes]
- Universitaet-GH Essen (Germany)
- Lawrence Berkeley Lab., CA (United States)
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.
- OSTI ID:
- 6718173
- Journal Information:
- Journal of the American Chemical Society; (United States), Journal Name: Journal of the American Chemical Society; (United States) Vol. 116:24; ISSN JACSAT; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400101 -- Activation
Nuclear Reaction
Radiometric & Radiochemical Procedures
400201* -- Chemical & Physicochemical Properties
ALKYNES
CHEMICAL ACTIVATION
CHEMICAL BONDS
CHEMICAL REACTIONS
COBALT COMPLEXES
COHERENT SCATTERING
COMPLEXES
DIFFRACTION
FURANS
HETEROCYCLIC COMPOUNDS
HYDROCARBONS
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
POLYCYCLIC SULFUR HETEROCYCLES
SCATTERING
TRANSITION ELEMENT COMPLEXES
X-RAY DIFFRACTION