Highly enantioselective copper-catalyzed conjugate addition of diethylzinc to enones using chiral spiro phosphoramidites as ligands

Novel monodentate chiral spiro phosphoramidite ligands have been readily synthesized in good yields from enantiomerically pure 1,1'-spirobiindane-7,7'-diol. The new ligands were highly efficient in the copper-catalyzed conjugate addition of Et(2)Zn to enones with up to 98% enantiomeric excess.     

Enantioselective copper-catalyzed conjugate addition of dialkyl zinc to nitro-olefins

[reaction: see text]The copper-catalyzed asymmetric conjugate addition of dialkylzinc onto various nitro-olefins has been carried out with excellent results. An enantiomeric excess of up to 94% was obtained using 0.5% Cu(OTf)2 and 1% of chiral trivalent phosphorus ligand.     

Copper-catalyzed enantioselective conjugate addition of diethylzinc using axially chiral aminoethyloxy-phosphine ligands

New axially chiral P,O,N-type ligands bearing both a diphenylphosphino group and 2-(dialkylamino)ethyloxy (or 2-pyridylmethyloxy) groups were designed and prepared along with P,O,O-type ligands by employing an easily available chiral component, (R)-2-hydroxy-2′-diphenylphosphinyl-1,1′-binaphthyl. Among the ligands the simplest P,O,N-type one bearing a 2-(dimethylamino)ethyloxy group was found to be the most efficient in copper-catalyzed enantioselective conjugate addition of diethylzinc to a cyclic enone, 2-cyclohexen-1-one, providing high enantioselectivity up to 99% ee.     

Enantioselective copper-catalyzed cyclopropanation of styrene by means of chiral bispidine ligands

Enantiopure C₁- and C₂-symmetric bispidine ligands have been synthesized and screened in the asymmetric copper-catalyzed cyclopropanation of styrene. In order to improve the enantiomeric excesses (ee) of the cyclopropane derivatives, the best performing C₁-symmetric diamine ligand was selected for studies on the reaction conditions. The optimized procedure allowed us to obtain up to 91% ee for the cis-cyclopropane derivative and up to 79% ee for the trans one.     

Biphenol-based phosphoramidite ligands for the enantioselective copper-catalyzed conjugate addition of diethylzinc

Phosphoramidite ligands, based on ortho-substituted biphenols and a chiral amine, induce high enantioselectivities (ee's up to 99%) in the copper-catalyzed conjugate addition of dialkylzinc reagents to a variety of Michael acceptors. Particularly, the best reported ee's were obtained for acyclic nitroolefins.     

Enantioselective copper-catalyzed allylic alkylation with dialkylzincs using phosphoramidite ligands

[reaction: see text]. In the presence of a catalytic amount of copper salts, cinnamyl halides undergo a regio- and enantioselective S(N)2' alkylation with dialkylzincs using chiral phosphoramidites as ligands. An S(N)2':S(N)2 ratio of 85:15 and enantiomeric excesses up to 77% for the chiral S(N)2' products are found. Variation of solvent and reaction temperature revealed that the highest regio- and enantioselectivities are found using coordinating solvents of -40 degrees C.     

Enantioselective rhodium-catalyzed addition of arylboronic acids to aldehydes using chiral spiro monophosphite ligands

[reaction: see text] Highly efficient rhodium-catalyzed asymmetric addition of arylboronic acids to aldehydes has been realized by using chiral spiro monophosphite ligands, affording diarylmethanols in excellent yields and good enantiomeric excesses.     

Design and synthesis of new bidentate alkoxy-NHC ligands for enantioselective copper-catalyzed conjugate addition

A new family of chiral alkoxy-N-heterocyclic carbene (NHC) ligands has been designed for the enantioselective copper-catalyzed conjugate addition of dialkylzincs to enones. These new bidentate NHC ligands were synthesized in high overall yields using a five-step procedure starting from commercially available β-aminoalcohols. Influence of the temperature, base, solvent and copper source were studied in order to optimize the stereoselectivity of the addition. High reactivity and excellent enantioselectivity were obtained at ambient temperature with a range of cyclic enones and dialkylzinc. Addition to acyclic enones has also been studied.     

Enantioselective addition of organometallics to aldehydes using camphor derived chiral 1,4-aminoalcohols as ligands

(+)-Camphor derived enantiomerically pure 1,4-aminoalcohols have been used as ligands in the addition reactions of n-BuLi and n-BuMgBr to benzaldehyde and in the reaction of diethylzinc with benzaldehyde and hexanal. All chiral secondary alcohols were obtained in good chemical yields and enantioselectivities were up to 87% ee in the addition of diethylzinc.     

Highly enantioselective copper-catalyzed conjugate addition of diethylzinc to cyclic enones with spirocyclic phosphoramidite ligands

A series of spirocyclic phosphoramidite ligands 6-9 with different substituents on the amine moiety were synthesized from the chiral spirocyclic diol (R)-5. These monodentate ligands have been applied in copper-catalyzed conjugate addition of diethylzinc to cyclic enones. Excellent enantioselectivities (up to 99% ee) can be achieved by the use of ligand (R,S,S)-9 bearing stereochemically matched structure derived from the C₂-symmetric (S,S)-bis(α-methylbenzyl)amine.     

Design and synthesis of new chiral pyridine–phosphite ligands for the copper-catalyzed enantioselective conjugate addition of diethylzinc to acyclic enones

A series of new chiral pyridine–phosphite ligands have been prepared from (R)-pyridyl alcohols and BINOL-derived chlorophosphite, and successfully employed in the copper-catalyzed enantioselective conjugate addition of diethylzinc to acyclic enones. Using the simple and inexpensive CuBr₂ as a precursor, the enantioselective additions to various substituted acyclic enones afforded products in high yields and good enantioselectivities (up to 92% ee).     

Solid-phase development of chiral phosphoramidite ligands for enantioselective conjugate addition reactions

The development of a method for the optimization of chiral ligands for the steric steering of enantioselective Cu-catalyzed conjugate additions of Znalkyls to enones is described. The method is based on combinatorial principles and solid-phase techniques. It includes the combinatorial synthesis of chiral bispidine-derived ligands embodying a phosphoramidite group on the solid phase and their investigation in immobilized form in the conjugate addition of ZnEt2 to cyclohexenone as test reaction. The best identified ligands were also synthesized separately and investigated in its soluble form. The results obtained for the polymer-bound ligands correctly mirrored the performance of the soluble ligands. The library embodied members giving ee values varying between 3 and 67%. The "positional scanning" approach proved to be invalid for the study of the ligand system, indicating that this approach in general should be applied with care. Taken together, the method allowed for rapid and efficient optimization of the ligands and led to the development of the first enantioselective, Cu-catalyzed conjugate addition reaction with a polymer-bound ligand.     

Enantioselective organocatalytic amine conjugate addition

The first enantioselective organocatalytic amine conjugate addition has been successfully developed. The application of LUMO-lowering iminium catalysis has enabled the highly chemo- and enantioselective 1,4-addition of a rationally designed N-silyloxycarbamate nucleophile (HOMO-raised) to alpha,beta-unsaturated aldehydes. Imidazolidinone 2*pTSA was found to catalyze the addition of various orthogonally N-protected silyloxycarbamate nucleophiles to a range of alpha,beta-unsaturated aldehydes, affording synthetically useful beta-amino aldehyde intermediates. The synthetic utility of the protocol was demonstrated in the rapid synthesis of enantioenriched beta-amino acids in one operation and 1,3-amino alcohol derivatives in three operations.     

Construction of a new type of chiral bidentate NHC ligands: copper-catalyzed asymmetric conjugate alkylation

We synthesized in three steps simple chiral bidentate NHC compounds that carry an achiral coordinating group as N-substituent and revealed that they serve as efficient chiral auxiliaries for the copper-catalyzed asymmetric conjugate addition of dialkylzinc to acyclic enones (up to 97% ee).     

Novel chiral bis(oxazolines): synthesis and application as ligands in the copper-catalyzed enantioselective conjugate addition of diethylzinc to enones

Novel chiral C₂-symmetric bis(oxazolines) were prepared from tartaric acid. They were applied as ligands in the copper-catalyzed conjugate addition of diethylzinc to chalcone and 2-cyclohexenone. Maximum enantiomeric excesses of 50% and 53% were obtained, respectively. The sense of induction was found to depend on the configuration of the stereogenic centre in the oxazoline ring, and not on the stereogenic centres of the 1,4-dioxane backbone.     

Enantioselective conjugate addition of a lithium ester enolate catalyzed by chiral lithium amides

Mixed aggregates of chiral lithium amide and lithium ester enolate have been employed in the enantioselective conjugate addition on alpha,beta-unsaturated esters. Michael adducts were obtained in ee's up to 76% combining a lithium enolate and a chiral 3-aminopyrrolidine lithium amide. The sense of the induction was found to be determined by both the relative configuration of the stereogenic centers borne by the amide and the solvent in which the reaction was conducted. [reaction: see text]     

Simple chiral diene ligands provide high enantioselectivities in transition-metal-catalyzed conjugate addition reactions

Chiral dienes possessing the bicyclo[2.2.2]octadiene framework were prepared readily through the [4 + 2] cycloaddition of ( R)-alpha-phellandrene with methyl propiolate as the key step. Diene 9, substituted with a tertiary alcohol on one of the two double bonds, is prepared in just one step from the cycloadduct and is highly effective as a chiral ligand for rhodium-catalyzed asymmetric conjugate addition reactions, giving the corresponding addition products with higher enantioselectivity than other chiral dienes.     

Enantioselective palladium-catalysed conjugate addition of arylsiloxanes

The complex formed from Pd(CH(3)CN)(4)(BF(4))(2) and (R,R)-MeDUPHOS is a highly enantioselective catalyst for the asymmetric conjugate addition of aryltriethylsiloxanes to a variety of unsaturated ketones, lactones and lactams.