Copper-Catalyzed Asymmetric Conjugate Addition of Trialkylaluminium Reagents to Trisubstituted Enones: Construction of Chiral Quaternary Centers
作者:Magali Vuagnoux-d'Augustin、Alexandre Alexakis
DOI:10.1002/chem.200701001
日期:2007.11.26
vinylalane species undergo enantioselective conjugateaddition 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]2C6H6) and tropos-phosphoramidite-based ligand. Thus, chiral quaternarycenters can be built, with up to 98% ee after rigorous
The copper-catalyzedasymmetricconjugateaddition of Grignard reagents to trisubstituted cyclic enones affords enantioenriched all-carbon quaternarycenters with up to 96% ee. The chiral ligand is a diaminocarbene, directly generated in situ. The combination of Grignard reagent and diaminocarbene is unprecedented in conjugateaddition, and the additon of the phenyl group, on such enones, cannot be
Formation of Quaternary Chiral Centers by N-Heterocyclic Carbene-Cu-Catalyzed Asymmetric Conjugate Addition Reactions with Grignard Reagents on Trisubstituted Cyclic Enones
The copper‐catalyzedconjugateaddition of Grignard reagents to 3‐substituted cyclic enones allows the formation of all‐carbon chiral quaternary centers. We demonstrate in this article that N‐heterocyclic carbenes act as efficient chiral ligands for this transformation. High enantioselectivities (up to 96 % ee) could be obtained for a variety of substrates.
The asymmetric construction of quaternary carbon centers by conjugateaddition of Grignard reagents to 3-methyl- and 3-ethylcyclohexenones was realized in a maximum enantioselectivity of 80% by using a C2 symmetric chiral N-heterocyclic carbene (NHC)-copper catalyst, generated from (4S,5S)-1,3-bis(2-methoxyphenyl)-4,5-diphenyl-4,5-dihydro-1H-imidazol-3-ium tetrafluoroborate and copper(II) triflate