Copper-Catalyzed Asymmetric Conjugate Addition of Trialkylaluminium Reagents to Trisubstituted Enones: Construction of Chiral Quaternary Centers

• Published in: Chemistry : a European journal 2007-01, Vol.13 (34), p.9647-9662
• Main Authors: Vuagnoux-d'Augustin, Magali, Alexakis, Alexandre
• Format: Article
• Language: English
• Subjects: aluminium; asymmetric catalysis; conjugate addition; copper; phosphoramidite ligands
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200701001

Me3Al, Et3Al, and vinylalane species undergo enantioselective conjugate addition to a wide range of 2‐ or 3‐substituted enones (cyclopent‐2‐enones, cyclohex‐2‐enones, 3‐methyl cyclohept‐2‐enone) in the presence of catalytic amount of copper salt (copper thiophene carboxylate, [Cu(CH3CN)4]BF4 or [CuOTf]2⋅C6H6) and tropos‐phosphoramidite‐based ligand. Thus, chiral quaternary centers can be built, with up to 98 % ee after rigorous optimization of experimental conditions. It was shown that the main important parameter was the order of the introduction of the reagents. Then, the generated enantioenriched aluminium enolates and the chiral conjugate adducts were functionalized and used for subsequent reactions. The enantioselective Cu‐catalyzed conjugate addition of Me3Al, Et3Al, and vinylalane species to a wide range of substituted enones in the presence of chiral phosphoramidite ligands is described (see scheme). Chiral quaternary centers can be built with up to 98 % ee. Then, enantioenriched aluminium enolates and chiral adducts were functionalized and used for subsequent reactions.