9 research outputs found
Copper-catalyzed asymmetric conjugate addition to various Michael acceptors : construction of all-carbon quarternary chiral centres
L'emploi des ligands de type phosphoramidite pour l'Addition Conjuguée Asymétrique (A.C.A.) catalysée par le cuivre d'espèces organozinciques (R₂Zn) ou organoaluminiques (R₃AI) sur des substrats disubstitués, cycliques ou acycliques, de géométrie exclusivement E ou Z, conduit à la formation d'adduits chiraux avec d'excellentes énantiosélectivités atteignant 99%. En outre, le caractère acide de Lewis de R₃AI permet une activation suffisante des substrats 2- ou 3-trisubstitués, et ainsi, l'obtention d'adduits cycliques possédant un centre quaternaire chiral avec une induction asymétrique atteignant 98% via l'A.C.A. catalysée par le cuivre. L'utilisation des énolates métalliques énantio-enrichis est étudiée aussi bien pour les systèmes di- que trisubstitués, avec notamment la formation d'acétates d'énol chiraux comme alternative à la synthèse d'éthers d'énol silylés. Enfin, l'utilisation ultérieure des adduits possédant un centre quaternaire chiral est envisagée afin de trouver diverses applications à la méthodologie développée, alors qu'une nouvelle réaction tandem d'hydroalumination-A.C.A. est mise au point
Tandem asymmetric conjugate addition-enolacetates formation of enantiomerically enriched zinc and aluminium enolates
The metal enolates, resulting from the copper-catalyzed enantioselective conjugate addition of organometallic reagents (Et2Zn or R3Al) to cyclic and acyclic enones are quantitatively trapped as enolacetates with acetic anhydride
Copper catalysed asymmetric conjugate addition of trialkylaluminuim reaggents to trisubstituted enones: construction of chiral quaternary centers
The Cu-catalyzed enantioselective conjugate addition of dialkylzinc to bis-alpha,beta-unsaturated carbonyl compounds followed by the intramolecular trapping of the zinc enolate in the presence of chiral phosphoramidite ligands was investigated. Cyclic and heterocyclic compounds with multichiral centers were formed as a mixture of two diastereomers with excellent diastereoselectivities (up to 99:1) and enantioselectivities (up to 94 % ee, ee=enantiomeric excess). The stereochemistry was determined to be trans,trans for the major products and trans,cis for the minor products. The absolute configuration of the cyclic compounds was assigned by comparison with the analogous adduct derived from trans-3-nonen-2-one and Et(2)Zn or the adduct obtained through conjugate addition of Me(2)Zn to trans-1-phenyl-non-2-en-1-one. Further transformation of these cyclic products into more complex compounds is under investigation in our laboratory
Enantioselective copper catalysed conjugate addition to 2- or 3- substituted cyclopent-2-ene-1-ones: Construction of stereogenic quaternary carbon centers
Trimethyl- and triethylaluminum undergo enantioselective conjugate addition to 2- and 3-substituted cyclopent-2-en-1- ones in the presence of catalytic amount of a copper salt and a phosphoramidite or a diphosphite ligand. Thus, chiral quaternary centers can be built with up to 93% ee
Formation of all-carbon chiral quaternary centers by copper catalysed asymmetric cojugate addition
Highly enantioselective copper(I)-phosphoramidite-catalysed additions of organoaluminium reagents to enones
Simple phosphoramidite ligands afford good to excellent levels of enantioselectivity in 1,4-additions of AlR3 species to enones; sequential carboalumination-ACA cascades are possible
Copper-catalyzed asymmetric conjugate addition of Grignard reagents to trisubstituted enones. Construction of all-carbon quaternary centers
The copper-catalyzed asymmetric conjugate addition of Grignard reagents to trisubstituted cyclic enones affords enantioenriched all-carbon quaternary centers 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 conjugate addition, and the additon of the phenyl group, on such enones, cannot be done by other conjugate addition methods
Formation of all-carbon quaternary centers by copper-catalysed asymmetric conjugate addition
This mini-review deals with a special, and challenging, aspect of the asymmetric conjugate addition: the formation of all-carbon quaternary centers by reaction with Michael acceptors bearing a polysubstituted unsaturation. Only copper catalysts allow this transformation, along with a careful choice of primary organometallics and chiral ligand. The resulting adducts are useful intermediates for the synthesis of more complex natural products
SimplePhos monodentate ligands: Synthesis and application in copper-catalysed reactions
A simple choice: Ligands termed SimplePhos (L*), based on a chiral amino and flexible aryl groups on the phosphorus atom, induce high enantioselectivity in the copper-catalyzed conjugate addition and allylic substitution of dialkyl zinc and trialkyl aluminum reagents (see scheme; CuTC=copper thiophene carboxylate)