Cationic but electron‐rich: Cyclopropenylylidene‐stabilized phospheniumcations exhibit the electron richness of classical trialkyl and triaryl phosphines even though they carry a positive charge stemming from a cationic substituent directly bonded to the phosphorous atom. These two facts have been exploited to synthesize gold catalysts that can be easily recycled after use.
Gold(I)-Catalyzed Enantioselective [4 + 2]-Cycloaddition of Allene-dienes
作者:Ana Z. González、F. Dean Toste
DOI:10.1021/ol902622b
日期:2010.1.1
An enantioselective gold(I)-catalyzed intramolecular [4 + 2]-cycloaddition of allenes and dienes is reported. The reactions allow for the asymmetric synthesis of trans-hexahydroindenes and pyrrolidine products using C3-symmetric phosphitegold(I) and ortho-arylphosphoramiditegold(I) complexes as catalysts, respectively.
A 1,3-bis-diphenylphosphine allene can give birth to new coordination complexes with palladium, platinum and gold metals. These complexes were fully characterized by NMR, HRMS and X-ray diffraction analysis. For gold(I),...
precursors. When armed with a methylene phosphine oxide moiety on the stereogenic center adjacent to the nitrogenatom, the corresponding bifunctional carbene ligands give rise to highly enantioselective heterocyclizations. DFT calculations brought some rationalization and highlighted the critical roles played by the phosphine oxide group and the tosylate anion in the asymmetric cyclization of γ-allenols
Accept it! Although the π‐acceptor properties of N‐heterocyclic carbenes (NHCs) are often considered negligible, they can be enhanced to the extent that they start to dominate the catalytic behavior of gold–NHC complexes (see scheme). As it seems to be easier to tune the π acidity of NHCs than to alter their σ‐donor properties, the general perception of this important class of ancillary ligands needs