Catalytic enantioselective aldol reaction to ketones

An enantioselective aldol reaction between ketones and ketene silyl acetals is described using CuF-chiral phosphine as a catalyst. The key for high enantioselectivity was the development of a novel ligand derived from Taniaphos combined with the unique accelerative effect of PhBF3K. These conditions are applicable to various substrates such as aromatic, aliphatic, and heteroaromatic ketones. In the case of substituted nucleophiles, the reaction proceeds well. The diastereoselectivity is independent of ketene silyl acetal geometry. This is the first example of a catalytic enantio- and diastereoselective aldol reaction to ketones using ketene silyl acetals.     

Catalytic enantioselective Reformatsky reaction with ketones

Chiral tertiary alcohols were obtained with good yields and enantioselectivities via a catalytic Reformatsky reaction with ketones, including the challenging diaryl ketones, using chiral BINOL derivatives.     

Catalytic enantioselective Strecker reaction of ketoimines

A new method for the catalytic enantioselective Strecker reaction (cyanation) of N-diphenylphosphinoyl ketoimines is described. The asymmetric catalyst is a chiral gadolinium complex prepared from Gd(OiPr)3 and the d-glucose-derived ligand 3 in a 1:2 ratio. The reaction has a broad substrate generality, giving high enantioselectivity from aromatic, ethyl, primary alkyl, and alpha,beta-unsaturated ketoimines. The products could be easily converted to disubstituted alpha-amino acids and their derivatives.     

Catalytic enantioselective Reformatsky reaction with ortho-substituted diarylketones

The catalytic enantioselective Reformatsky reaction with ortho-substituted diarylketones with good enantioselectivities and moderate to good yields is reported. A readily available BINOL derivative is used as a chiral catalyst, and the reactions are performed with ethyl iodoacetate as a nucleophile and Me2Zn as the zinc source. The presence of air was found to be crucial to achieve an effective C-C bond formation pointing to a radical mechanism.     

Catalytic enantioselective intermolecular reductive aldol reaction to ketones

We describe the first example of a catalytic enantioselective intermolecular reductive aldol reaction. Three types of reactions were studied: (1) reactions between acetophenone and methyl acrylate; (2) reactions between symmetric ketones and β-substituted α,β-unsaturated esters; and (3) reactions between acetophenone derivatives and an allenic ester. Although only moderate enantioselectivity was obtained in the first reaction type, high to excellent enantioselectivity was realized in the enantio-induction at the α-position in the second reaction type and at the δ-position in the third reaction type. Specifically, the third reaction type afforded the corresponding tertiary alcohols with up to 99% ee. Pre-activation of the nucleophile by silyl enolate formation is not necessary in these one-pot catalytic enantioselective reductive aldol reactions.     

Catalytic enantioselective aza-Henry reaction with broad substrate scope

In situ generated azomethines from readily available precursors react with nitromethane in the presence of 120 mol % of CsOH.H2O and 12 mol % of quinine- and cinchonidine-derived quaternary ammonium chlorides to provide the corresponding aza-Henry adducts in good yields and very high selectivities. It represents the first general enantioselective aza-Henry method for azomethines derived from enolizable aldehydes, giving rise to enantiomeric excesses above 94%. In addition, the reactions with nitroethane afforded high diastereo- and enantioselectivities (syn:anti up to 95:5; up to 98% ee for syn).     

Catalytic enantioselective oxaziridination

The first catalytic enantioselective synthesis of oxaziridines is presented. The oxidation of aryl and alkyl aldimines with m-CPBA under organocatalytic conditions using cinchona alkaloid-derived catalysts furnished optically active oxaziridines in good yields and high enantioselectivities (up to 94% ee). Mechanistic investigations indicate a stepwise enantioselective oxidation process.     

Copper/silver-cocatalyzed Conia-ene reaction of linear beta-alkynic beta-ketoesters

A novel and general copper/silver catalytic system has been developed for the Conia-ene intramolecular reaction of linear beta-alkynic beta-ketoesters. In the presence of (CuOTf)2.C6H6 and AgSbF6 (or AgOAc), a variety of the linear beta-alkynic beta-ketoesters selectively underwent the Conia-ene intramolecular reaction in moderate to good yields.     

Catalytic asymmetric domino Michael addition-alkylation reaction: enantioselective synthesis of dihydrofurans

A catalytic enantioselective synthesis of dihydrofurans has been developed. 1,3-Dicarbonyl derivatives react with (E)-β,β-bromonitrostyrenes in the presence of a chiral bifunctional thiourea catalyst providing mild and efficient access to diverse polysubstituted dihydrofurans in good yields and enantioselectivities.     

Catalytic enantioselective Diels-Alder reaction via a chiral indium(III) complex

[reaction: see text] A chiral indium complex has been developed to effect high enantioselectivities in catalyzing enantioselective Diels-Alder reaction. The cycloaddition of a variety of cyclic and open-chained dienes to 2-methacrolein and 2-bromoacrolein resulted in good yields and excellent enantioselectivities (up to 98% ee).     

Catalytic enantioselective decarboxylative protonation

We report a highly enantioselective, general catalytic system for the facile synthesis of tertiary stereocenters by protonation adjacent to cyclic ketones. The method relies on catalytic decarboxylative protonation of readily accessible racemic quaternary beta-ketoesters. A range of substituted cycloalkanone compounds can be accessed through this process with high levels of enantioselectivity.     

Catalytic addition of alkenylzirconocene chloride to 3,4-dihydroisoquinoline and its enantioselective reaction

The addition of alkenylzirconocene chloride to 3,4-dihydroisoquinoline in the presence of a stoichiometric amount of acylating agent such as (Boc)₂O or ClCOOC₂H₅ was carried out in the presence of a catalytic amount of Cu(I) (10 mol %) to give an alkenylation-carbamation product. The enantioselective addition (56-75%ee) of the alkenylzirconocene chloride was also achieved under Cu(I)/chiral amine (10 mol %) conditions.     

Catalytic enantioselective allylation of ketoimines

A general catalytic allylation of simple ketoimines was developed using 1 mol % of CuF.3PPh(3) as catalyst, 1.5 mol % of La(O(i)Pr)(3) as the cocatalyst, and stable and nontoxic allylboronic acid pinacol ester as the nucleophile. This reaction constituted a good template for developing the first catalytic enantioselective allylation of ketoimines. In this case, using LiO(i)Pr as the cocatalyst produced higher enantioselectivity and reactivity than La(O(i)Pr)(3). Thus, using the CuF-cyclopentyl-DuPHOS complex (10 mol %) and LiO(i)Pr (30 mol %) in the presence of (t)BuOH (1 equiv) produced high enantioselectivity up to 93% ee from a range of aromatic ketoimines. Mechanistic studies indicated that LiO(i)Pr accelerates the reaction by increasing the concentration of an active nucleophile, allylcopper.     

Catalytic enantioselective hydroboration of cyclopropenes

2,2-Disubstituted cyclopropyl boronates have been synthesized with high degrees of diastereo- and enantioselectivity via the rhodium-catalyzed asymmetric hydroboration of 3,3-disubstituted cyclopropenes. A strong directing effect of ester and alkoxymethyl substituents has been demonstrated. The directing effect was found to be necessary in achieving high degrees of enantiomeric induction. Selected cyclopropylboronic derivatives were successfully employed in the Suzuki cross-coupling reaction to produce the corresponding optically active aryl- and vinylcyclopropanes in good yields.