Gold-Catalyzed [4C+2C] Cycloadditions of Allenedienes, including an Enantioselective Version with New Phosphoramidite-Based Catalysts: Mechanistic Aspects of the Divergence between [4C+3C] and [4C+2C] Pathways
作者:Isaac Alonso、Beatriz Trillo、Fernando López、Sergi Montserrat、Gregori Ujaque、Luis Castedo、Agustí Lledós、Jose L. Mascareñas
DOI:10.1021/ja905415r
日期:2009.9.16
Gold(I) complexes featuring electron acceptor ligands such as phosphites and phosphoramidites catalyze the [4C+2C] intramolecular cycloaddition of allenedienes. The reaction is chemo- and stereoselective, and provides trans-fused bicyclic cycloadducts in good yields. Moreover, using novel chiral phosphoramidite-based gold catalysts it is possible to perform the reaction with excellent enantioselectivity
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