| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 5279645 | Tetrahedron Letters | 2010 | 5 Pages |
The mechanism of PBu3-catalyzed homodimerization of ketoketenes has been explored and compared with that of the previously reported trialkylphosphite-mediated reactions. NMR studies of the PBu3-catalyzed reaction implicated the involvement of tetravalent phosphonium intermediates. Phosphonium intermediates in the catalytic cycle were trapped through reaction with trimethylsilyl chloride and 4-chlorobenzaldehyde, and the resulting products were characterized. A method for the stoichiometric generation of phosphonium enolates was developed as a result of these studies. No evidence was obtained for the involvement of pentacovalent phosphorane intermediates in trialkylphosphine-catalyzed ketoketene homodimerization reactions, in contrast with the mechanism of the trialkylphosphite-mediated homodimerization of dimethylketene. An X-ray crystal structure analysis of methylphenylketene dimer showed that it possesses Z-geometry about the exocyclic olefin.
Graphical abstractThe mechanism of the PBu3-catalyzed homodimerization of ketoketenes has been investigated and compared with that of the previously reported P(OMe)3-mediated homodimerization of dimethylketene. NMR studies and intermediate trapping experiments of the PBu3-catalyzed reaction implicated the involvement of tetravalent phosphonium enolate intermediates.Figure optionsDownload full-size imageDownload as PowerPoint slide
