Catalytic enantioselective synthesis of β-trifluoromethyl pyrrolines

Enantioselective synthesis of β-trifluoromethylated pyrrolines has been developed by the organocatalyzed-conjugated addition of nitromethane to β-trifluoromethylated enones, followed by a nitro-reduction/cyclization/dehydration sequence in a one-pot procedure with 97-98% ees.     

First enantioselective reductive amination of α-fluoroenones

From α-fluoroenones 2, a synthesis of (E) ketone oxime O-alkyl ethers 5 is reported with good to excellent yields. Then the first enantioselective reduction of these ketimines, via oxazaborolidine, is described with moderate to good enantiomeric excesses, leading to valuable chiral fluoroallylic amines 1.     

Catalytic enantioselective synthesis of chiral γ-butyrolactones

A tandem catalytic asymmetric aldol reaction/cyclization of β,γ-didehydro-γ-lactones with aldehydes was achieved using chiral tin dibromide as a chiral precatalyst and sodium alkoxide as a base precatalyst. Optically active trans-β,γ-disubstituted γ-butyrolactones were selectively obtained in moderate to high yields with up to 99% ee from γ-aryl-substituted β,γ-didehydro-γ-butyrolactones and bulky aliphatic aldehydes.     

Highly enantioselective copper-catalyzed electrophilic trifluoromethylation of β-ketoesters

Enantioselective Cu-catalyzed trifluoromethylation of β-ketoesters using commercially available trifluoromethylating reagents is reported. A number of α-CF(3) β-ketoesters are obtained with up to 99% ee. The trifluoromethylated products were then transformed diastereoselectively to α-CF(3) β-hydroxyesters with two adjacent quaternary stereocenters via a Grignard reaction.     

Kinetic resolution of β-lactams via enantioselective N-acylation

Enantioselective N-acylation of 4-aryl-β-lactams in the presence of acyl transfer catalyst Cl-PIQ provides an effective method for their non-enzymatic kinetic resolution.     

A new enantioselective synthesis of β-amino acids

Enantioselective hydrogenation of some α,β-unsaturated nitriles and their corresponding methyl esters bearing a phthalimidomethyl substituent at the α-carbon using Rh-DuPHOS catalysts afforded β-amino acid precursors with modest e.e.s of up to 48%. Hydrogenation of the α,β-unsaturated methyl esters using a Ru-BINAP catalyst gave higher e.e.s of up to 84%. Method development for the determination of the enantiomeric excesses of these derivatives using chiral HPLC is also reported.     

An enantioselective formal synthesis of （-）-thujopsene

Dihydromayurone （3）, a key intermediate to synthesize （-）-thujopsene （1）, was efficient enantiocontrolled synthesized from （＋）-dihydrocarvone through 9 steps in an overall yield of 19.3%. The key step was the Simmons-Smith reaction.     

Ru-catalyzed highly enantioselective hydrogenation of α-keto Weinreb amides

Asymmetric hydrogenation of α-keto Weinreb amides has been realized with [Ru((S)-Sunphos)(benzene)Cl]Cl as the catalyst and CeCl 3·7H2O as the additive.A series of enantiopure α-hydroxy Weinreb amides(up to 97% ee) have been obtained.Catalytic amount of CeCl3·7H2O is essential for the high reactivity and enantioselectivity and the ratio of CeCl3·7H2O to [Ru((S)-Sunphos)(benzene)Cl]Cl plays an important role in the hydrogenation reaction.     

Organocatalytic α-amination-allylation-RCM strategy: enantioselective synthesis of cyclic hydrazines

A highly enantioselective method for the synthesis of cyclic hydrazines by using organocatalytic α-amination-allylation-RCM strategy is described. Proline-catalyzed α-amination of aldehydes followed by indium-mediated one-pot allylation of the crude α-hydrazino aldehydes produces 1,2-aminoalcohols in high enantio- and diastereoselectivities. The 1,2-aminoalcohols are further converted into cyclic hydrazines by using ring-closing metathesis (RCM) reaction.     

Silicon-mediated enantioselective synthesis of structurally diverseα-amino acid derivatives

The catalytic asymmetric synthesis of novel and chiral amino acid derivatives with unconventional chemo-, diastereo-, and enantio-selectivity remains a paramount challenge. Herein we reported a novel protocol for the use of highly enantioselective copper-catalyzed cycloaddition of α,β-unsaturated acylsilanes as a springboard reaction for the facile synthesis of structurally diversified pyrrolidines and complicated α-amino esters by desilylation. The newly developed process could provide a wide range of synthetically useful acylsilane-substituted pyrrolidines(ASiP) in high yields and excellent diastereo-and enantioselectivities with Cu/(R)-XylBINAP complex as the catalyst. And the downstream desilylation transformation enables to expand the potntial applications of 1,3-dipolar cycloaddition in the construction of structurally unique amino acid derivatives, in which an unprecedented and concerted fluoride anion-promoted C–X(X=H, Si, N, C) bond cleavage occurred to the enantioselective construction of aldehyde-substituted pyrrolidines, linear cinnamaldehyde or alkene-substituted amino esters in high ee values.     

Catalytic enantioselective synthesis of β-amino alcohols by nitrene insertion

Chiral β-amino alcohols are important building blocks for the synthesis of drugs, natural products, chiral auxiliaries, chiral ligands and chiral organocatalysts. The catalytic asymmetric β-amination of alcohols offers a direct strategy to access this class of molecules. Herein, we report a general intramolecular C(sp³)–H nitrene insertion method for the synthesis of chiral oxazolidin-2-ones as precursors of chiral β-amino alcohols. Specifically, the ring-closing C(sp³)–H amination of N-benzoyloxycarbamates with 2 mol% of a chiral ruthenium catalyst provides cyclic carbamates in up to 99% yield and with up to 99% ee.The method is applicable to benzylic, allylic, and propargylic C–H bonds and can even be applied to completely non-activated C(sp³)–H bonds, although with somewhat reduced yields and stereoselectivities. The obtained cyclic carbamates can subsequently be hydrolyzed to obtain chiral β-amino alcohols. The method is very practical as the catalyst can be easily synthesized on a gram scale and can be recycled after the reaction for further use. The synthetic value of the new method is demonstrated with the asymmetric synthesis of a chiral oxazolidin-2-one as intermediate for the synthesis of the natural product aurantioclavine and chiral β-amino alcohols that are intermediates for the synthesis of chiral amino acids, indane-derived chiral Box-ligands, and the natural products dihydrohamacanthin A and dragmacidin A.     

A very enantioselective photodeconjugation of α,β-unsaturated esters

An enantiomeric excess up to 70% can be obtained in the photodeconjugation of conjugated esters in the presence of (1R, 2S) 1-phenyl, 2-isopropylamino-propanol.     

Kinetic resolution of N-acyl-β-lactams via benzotetramisole-catalyzed enantioselective alcoholysis

The first nonenzymatic kinetic resolution of β-lactams has been achieved. Alcoholysis of their N-aroyl derivatives in the presence of a simple chiral acyl transfer catalyst, benzotetramisole, produces β-amino acid derivatives with excellent enantioselectivity.     

Chiral Brønsted acid catalyzed enantioselective allenylation of aldehydes

A versatile and highly enantioselective chiral Br?nsted acid-catalyzed allenylation of aldehydes with propargyl borolane is reported. The reaction is shown to be practical and quite general with a broad substrate scope covering aryl, heteroaryl, α,β-unsaturated, and aliphatic aldehydes.     

Highly enantioselective synthesis of β-hydroxysulfonamides by asymmetric transfer hydrogenation

A series of optically active β-hydroxy sulfonamides were synthesized for the first time by asymmetric transfer hydrogenation of the corresponding β-ketosulfonamides using the Ru-TsDPEN-HCOOH-Et₃N catalytic system, in excellent yields (up to 95%) with excellent diastereo- (up to > 99:1 dr) and enantioselectivities (up to >99% ee).     

Rapid screening of hydrolases for the enantioselective conversion of ‘difficult-to-resolve’ substrates

Hydrolases showing high enantioselectivity towards three racemic alcohols (1-methoxy-2-propanol, 3-hydroxy-tetrahydrofuran, 3-butyn-2-ol) and pantolactone were identified by a step-wise screening procedure. Initially, those biocatalysts, which exhibited hydrolytic activity towards the corresponding acetates or butyrates, were selected out of >100 enzymes. Here, rapid screening was performed in a pH-indicator, based format in microtiter plates. Subsequently, enantioselectivity of active hydrolases was determined in small scale reactions (∼1 mg substrate per reaction) by means of gas chromatography using chiral columns. Enzymes exhibiting highest enantioselectivities were then chosen for preparative scale resolution. Using this strategy, at least one suitable hydrolase was found for 3 out of the 4 model compounds examined, allowing efficient kinetic resolution. Moreover, in all cases enantiocomplementary enzymes were identified thus enabling access to both enantiomers of all substrates.     

A new series of chiral catalysts for the enantioselective borane reduction of ketones

A new series of 1,3,2-oxazaborolidine catalysts substituted in position 4 by the (CH3)3C(CH2)n group (n=2, 3, 4, 5) were synthesized and applied to the borane reduction of prochi-ral ketones. The relationship between catalyst structure and enantioselectivity was discussed.     

Baker''''s yeast mediated reduction of substituted acenaphthenequinones: Regio-and enantioselective preparation of mono-hydroxyacenaphthenones

Baker's yeast mediated reduction of acenaphthenequinone within 4-10 h afforded mono-hydroxyacenaphthenone mainly with low enantioselectivity, the substrate and mono-hydroxyacenaphthenone product almost converted to dihydroxyacenaphthene after 48 h. By control of the reaction time and in the presence of DMF as co-solvent, the reduction of 6-substituted acenaphthenequinones under vigorous agitation afforded the corresponding 2-hydroxyacenaphthenones in 24-84% yields with 10-93% ee.