Highly enantioselective synthesis of α-fluoro-α-nitro esters via organocatalyzed asymmetric Michael addition

Primary amines catalyzed the asymmetric Michael addition of ethyl 2-fluoro-2-nitroacetate to enones to provide chiral α-fluoro-α-nitro ester ketones with two contiguous stereogenic centers, one of which is a fluorinated quaternary chiral center, with excellent enantioselectivities and in moderate to good yields.     

Convenient,asymmetric synthesis of enantiomerically pure 2′,6′-dimethyltyrosine (DMT) via alkylation of chiral equivalent of nucleophilic glycine

Asymmetric synthesis of (S)-2′,6′-dimethyltyrosine (DMT) via reactions of 4′-benzyloxy-2′,6′-dimethylbenzyl bromide with Ni(II)-complexes of the chiral Schiff base of glycine with (S)-o-[N-(N-benzylprolyl)amino]benzophenone was developed. Inexpensive and readily available reagents and solvents involved, including recyclable chiral auxiliary, simplicity of the experimental procedures and high chemical yields, make this method synthetically attractive for preparing the target amino acids on a multi-gram scale.     

Highly diastereo- and enantioselective organocatalytic michael addition of α-ketoamides to nitroalkenes

The first organocatalytic enantio- and diastereoselective conjugate addition of α-ketoamides to nitroalkenes has been achieved using a bifunctional amino thiourea catalyst. In this new approach, the substrate amide proton plays a critical role in the formation of the Michael anti-adducts in high yields and high stereoselectivities. To illustrate the high synthetic potential of this methodology, the diastereo- and enantioselective synthesis of a hexasubstituted cyclohexane via a Michael-Michael-Henry cascade reaction is described.     

A diastereo- and enantioselective Michael addition of chiral amide enolates to α, β-unsaturated esters a stereoelective synthesis of (+)-dehydroiridodiol and (−)-isodehydroiridodiol

(+)-Dehydroiridodiol and (−)-isodehydroiridodiol were synthesized stereoselectively using the diastereo- and enantioselective Michael addition of chiral amide enolates to α, β-unsaturated esters.     

Chiral squaramides catalyzed diastereo- and enantioselective Michael addition of α-substituted isocyanoacetates to N-aryl maleimides

An efficient diastereo- and enantioselective Michael addition of α-substituted isocyanoacetates to N-aryl maleimides catalyzed by quinine or cyclohexane-1,2-diamine derived squaramide catalysts has been disclosed, affording the corresponding adducts in good yields (up to 99%), high diastereoselectivities (up to >20:1 dr) and good to excellent enantioselectivities (up to 94% ee) under mild conditions.     

Novel and practical asymmetric synthesis of β2,3-amino esters using asymmetric Michael addition of chiral amine

A practical method for the synthesis of chiral β^2,3-amino esters having various substituents was developed, which is characterized by an asymmetric Michael addition reaction of a chiral lithium amide with trisubstituted (E)-α,β-unsaturated esters. We found that a highly face-selective protonation occurred by the quick addition of water to the enolate intermediate derived from the Michael addition reaction to afford N-protected β^2,3-amino esters in moderate to excellent yields. This finding was made possible by the facile preparation of geometrically pure trisubstituted (E)-α,β-unsaturated esters, which was established recently by our group. The subsequent deprotection of the amino group in the Michael adduct by using N-iodosuccinimide (NIS) efficiently provided β^2,3-amino esters having various substituents.     

BINOL-based azacrown ether catalyzed enantioselective Michael addition: asymmetric synthesis of α-aminophosphonates

Several novel 1,1′-bi-2-naphthyl-appended azacrown ethers with donor side-arms were synthesized and applied for the first time as chiral catalysts in the asymmetric Michael addition of an N-protected aminomethylenephosphonate onto acrylonitriles, resulting in high diastereoselectivity and enantioselectivity. The absolute configuration of the adduct was determined from its experimental and calculated CD spectra.     

Enantioselective synthesis of functionalized α-amino acids via a chiral guanidine catalyzed Michael addition reaction

Several chiral guanidines were evaluated as catalysts for the Michael reaction of glycine derivatives 7 with acrylic esters 8. The best result (30.4% ee) was obtained when 7b was reacted with 8b under the catalysis of guanidine 1 in THF.     

TiCl4 promoted menthyl ester chiral auxiliary mediated synthesis of chiral syn-β-amino esters and applications of a representative syn-β-amino ester

β-Amino esters were obtained in up to 78% yield with 72:28–96:4 diastereomeric ratios by the reaction of the chiral titanium enolate of menthyl esters, prepared using the TiCl₄/Et₃N reagent system with prochiral imines. A representative syn-β-amino ester derivative has been used for the resolution of racemic mandelic acid to obtain a sample with >99% ee in a single step. A representative syn-β-amino ester was converted to the corresponding N-deprotected amino ester using the Pd–C/HCOOH reagent system, and then to the corresponding β-amino acid using the glacial CH₃COOH/HCl reagent system, and to the corresponding β-lactam derivative with partial epimerization by the reaction using C₂H₅MgBr.     

Enzymatic diastereo- and enantioselective synthesis of α-alkyl-α,β-dihydroxyketones

An enzymatic strategy for the preparation of optically pure α-alkyl-α,β-dihydroxyketones is reported. Homo- and cross-coupling reactions of α-diketones catalyzed by acetylacetoin synthase (AAS) produce a set of α-alkyl-α-hydroxy-β-diketones (30-60%, ee 67-90%), which in turn are reduced regio-, diastereo-, and enantioselectively to the corresponding chiral α-alkyl-α,β-dihydroxyketones (60-70%, ee >95%) using acetylacetoin reductase (AAR) as catalyst. Both enzymes are obtained from Bacillus licheniformis and used in a crude form. The relative syn stereochemistry of the enantiopure α,β-dihydroxy products is assigned by NOE experiments, whereas their absolute configuration is determined by conversion of the selected 3,4-dihydroxy-3-methyl-pentan-2-one to the natural product (+)-citreodiol.     

Chiral Brønsted acid-catalyzed diastereo- and enantioselective synthesis of CF(3)-substituted aziridines

A multicomponent organocatalyzed highly diastereo- and enantioselective synthesis of CF(3)-substituted aziridines is described. This reaction of in situ generated CF(3)CHN(2) and aldimines was realized by chiral Br?nsted acid catalysis. The utility of the products is illustrated by easy access to β-CF(3) isocysteine and aziridine-containing dipeptides.     

Highly enantioselective synthesis of γ-substituted butenolides via the vinylogous Mukaiyama-Michael reaction catalyzed by a chiral scandium(III)-N,N'-dioxide complex

A highly efficient catalytic asymmetric vinylogous Mukaiyama-Michael reaction of the 2-silyloxyfuran with chalcone derivatives, catalyzed by a chiral N,N'-dioxide-scandium(III) complex, has been accomplished which tolerates a wide range of substrates. The reaction proceeds with complete regioselectivities, excellent diastereoselectivities (up to >99?:?1 dr) and good to excellent enantioselectivities (up to 94% ee) under mild conditions, delivering highly functionalized enantiomerically enriched anti-γ-substituted butenolides. The process is air-tolerant and easily manipulated with available reagents. In order to illustrate the synthetic potential of this reaction, the gram-scale synthesis and the elaboration of the butenolides have been explored. On the basis of the experimental results, a possible catalytic cycle and favorable stereorecognition model have been proposed.     

Highly regio-, diastereo- and enantioselective one-pot gold/chiral Brønsted acid-catalysed cascade synthesis of bioactive diversely substituted tetrahydroquinolines

One-pot sequential asymmetric reactions of aminobenzaldehydes or aminophenones with alkynes catalysed by a gold(i)/Br?nsted acid cooperative system are reported. This process provides a highly efficient method for the synthesis of optically active tetrahydroquinolines, with one or two chiral centres at different positions as well as highly divergent functional groups, in good to excellent yields and with high regio-, diastereo- and enantioselectivities. A preliminary study on the effect of stereochemistry on biological activity suggests a potential application of these optically active tetrahydroquinolines in drug discovery processes.     

Asymmetric synthesis of α,β-substituted γ-amino acids via conjugate addition

The first conjugate addition reaction of organocuprates to N-enoyl oxazolidinone where a N-protected γ-nitrogen atom and an α-methyl group are present into α, β-unsaturated system is described. This reaction gave anti-products in moderate yields and high diastereomeric ratios. The anti-products have two contiguous stereogenic centers, one formed by the conjugate addition reaction and the other by a diastereoselective protonation reaction. The removal of chiral oxazolidinone moiety and N-deprotection of amino group furnished chiral α, β-disubstituted γ-amino acids.     

Asymmetric synthesis of sterically and electronically demanding linear ω-trifluoromethyl containing amino acids via alkylation of chiral equivalents of nucleophilic glycine and alanine

An operationally convenient, scalable asymmetric synthesis of linear, ω-trifluoromethyl-containing amino acids, which were not previously produced in their enantiomerically pure form, has been developed via alkylation of chiral equivalents of nucleophilic glycine and alanine. The simplicity of the experimental procedures and high stereochemical outcome (yields up to 90% and diastereoselectivity up to 99%) of the presented method render these fluorinated amino acids readily available for systematic medicinal chemistry studies and de novo peptide design.     

Diastereo- and enantioselective synthesis of anti-1,3-mercapto alcohols from α,β-unsaturated ketones via tandem Michael addition–MPV reduction

A new and effective asymmetric synthesis of anti-1,3-mercapto alcohols 3 from α,β-unsaturated ketones 1 utilizing tandem Michael addition–Meerwein–Ponndorf–Verley (MPV) reduction is described. Transformation of the MPV products anti-4 via the Wagner–Meerwein rearrangement was optimized under acidic or basic conditions to afford 1,3-mercapto alcohols anti-3, depending on the substituent R² of 4.     

Highly diastereo- and enantioselective aldol reaction of methyl α-isocyanoacetate: a cooperative catalysis approach

The cooperative catalyst activity between a chiral transition-metal catalyst and an achiral organocatalyst has been identified as one of the critical asymmetric reaction optimization components in the highly diastereo- and enantioselective aldol reaction of methyl α-isocyanoacetate.     

Highly effective and enantioselective Michael addition of 4-hydroxycoumarin to α,β-unsaturated ketones promoted by simple chiral primary amine thiourea bifunctional catalysts

Highly asymmetric Michael addition of 4-hydroxycoumarin to α,β-unsaturated ketones promoted by chiral primary amine thiourea bifunctional catalysts was developed and a series of Michael adducts were obtained in excellent yields (up to 97%) and enantioselectivities (up to 95% ee). Optically pure S-warfarin was easily obtained in 99% ee after single recrystallization.     

Asymmetric synthesis of 3-substituted pyrrolidones via α-alkylation of a chiral non-racemic γ-lactam

3-Alkyl pyrrolidones 9 were synthesized in good yield and high diastereoselectivity by α-alkylation of the new chiral non-racemic lactam 8 derived from (R)-(−)-phenylglycinol. After debenzylation and introduction of an electron-withdrawing group, 3-methylpyrrolidone 10 is easily hydrolyzed in a basic medium to produce γ-aminobutyric acid (GABA) analogue 13.