Catalytic asymmetric Mannich-type reactions of α-cyano α-sulfonyl carbanions

An efficient asymmetric Mannich-type reaction of α-cyano α-sulfonyl carbanions has been achieved by exploiting the structural modularity and anion-recognition ability of chiral 1,2,3-triazolium ions. This protocol has proven to be applicable to a variety of N-Boc imines and cyanosulfones, affording β-amino α-cyanosulfones in excellent yields with high stereoselectivities.     

Synthesis and application of an IL-supported diol as protecting group for aldehydes

A new IL-supported diol,1-(2,3-dihydroxypropyl)-3-methylimidazolium hexafluorophosphate has been synthesized and char- acterized by FT-IR,~1H NMR,~(13)C NMR and MS (ESI).Its physical properties such as freezing point,solubility and specific gravity and thermal stability were determined.Synthetic utilities of the resultant diol as a protecting group for aldehydes were also investigated.     

Synthesis and photochemical reactivity of caged glutamates with a π-extended coumarin chromophore as a photolabile protecting group

‘Caging’ and ‘uncaging’ bioactive substrates are key techniques in studying a wide variety of biological processes. In the present study, two-types of novel caged glutamates with a two-photon absorption (TPA) core, that is, π-extended coumarin, were synthesized and their photochemical release of glutamate was analyzed. The high yields of glutamate (>92%) were observed in the photolysis of compounds 1 and 10, respectively.     

Synthetic study on neoponkoranol and its side chain epimer as potent α-glucosidase inhibitors,optimization of protecting group

Coupling reaction between thiosugar and triflate as the key protocol to synthesize neoponkoranol, a naturally occurring potent α-glucosidase inhibitor, and its related sulfonium salts was optimized by applying different esters as protecting group, with the yields of desired products being greatly improved. Our proposed mechanism of the coupling reaction indicated that the nucleophilicity of C3-hydroxyl moiety on monosaccharide structure is closely related to the reaction mode.     

Scyllo-inositol as a convenient protecting group for aryl boronic acids in Suzuki–Miyaura cross-coupling reactions

Herein, we report air- and water-stable borate complexes between scyllo-inositol and aryl boronic acids. The complexes were less reactive than free aryl boronic acids under Suzuki–Miyaura cross-coupling reaction conditions; thus, the borate complexes were used as protected boronic acids. Although protecting groups for organoboronic acids are useful in coupling reactions, especially those used to produce π-conjugated molecules, only a few reports describing the use of protecting groups for boronic acids have been published. The proposed unique structural borate complex provides a novel protective method for aryl boronic acids.     

Catalysis of highly stereoselective Mannich-type reactions of ketones with α-imino esters by a pyrrolidine-sulfonamide. Synthesis of unnatural α-amino acids

The novel pyrrolidine-sulfonamide I has been prepared and used successfully to catalyze Mannich-type reactions between ketones and α-imino esters. The process is used to efficiently synthesize functionalized α-amino acid derivatives with excellent levels of regio-, diastereo-, and enantio-selectivity.     

Catalytic asymmetric vinylogous Mannich-type (AVM) reaction of nonactivated α-angelica lactone

A direct highly diastereo- and enantioselective asymmetric vinylogous Mannich-type (AVM) reaction of aldimines with nonactivated natural α-angelica lactone has been successfully developed. It was demonstrated that the nonactivated natural α-angelica lactone is a useful vinylogous nucleophile to give the chiral δ-amino γ,γ-disubstituted butenolide carbonyl derivatives. The N,N'-dioxide L2-Sc(III) complex is efficient toward the obtention of a range of corresponding products with adjacent quaternary and tertiary stereocenters in excellent dr and ee values.     

Syntheses of α-pyrones using gold-catalyzed coupling reactions

Sequential alkyne activation of terminal alkynes and propiolic acids by gold(I) catalysts yields compounds having α-pyrone skeletons. Novel cascade reactions involving propiolic acids are reported that give rise to α-pyrones with different substitution patterns.     

Solventless DBU-promoted Mannich-type reactions of α-amido p-tolylsulfones with diethyl fluoromalonates and diethyl malonates

Mannich-type reactions of α-amido p-tolylsulfones with diethyl fluoromalonates and diethyl malonates, respectively in presence of catalytic amount of DBU have been developed. A variety of α-amido p-tolylsulfones prepared from aromatic and aliphatic aldehydes reacts with diethyl fluoromalonates and diethyl malonates, respectively under mild reaction conditions to afford α-fluoro β-amino esters and β-amino esters in moderate to good yield.     

Synthesis and cycloaddition reactions of α-substituted acrolein dimethylhydrazones containing an acetal group

A series of new -substituted acrolein dimethylhydrazones containing an acetal group were synthesized. These hydrazones react with acrylonitrile or methyl acrylate according to the Diels—Alder reaction pattern to give substituted tetrahydropyridines. An unusual [2+4]- and [2+3]-cycloaddition cascade reaction involving -diethoxymethylacrolein dimethylhydrazone was discovered.     

Direct Deprotonative Functionalization of α,α-Difluoromethyl Ketones using a Catalytic Organosuperbase

The deprotonative functionalization of α,α-difluoromethyl ketones is described herein. Using a catalytic organosuperbase and a silane additive, the corresponding difluoroenolate could be generated and trapped with aldehydes to deliver various α,α-difluoro-β-hydroxy ketones in high yields. This new strategy tolerates numerous functional groups and represents the access to the difluoroenolate by direct deprotonation of the difluoromethyl unit. The diastereoselective version of the reaction was also investigated with d.r. up to 93 : 7. Several transformations were performed to demonstrate the synthetic potential of these α,α-difluoro-β-hydroxy ketones. In addition, this method has been extended to the use of other electrophiles such as imines and chalcogen derivatives, and a difluoromethyl sulfoxide as nucleophile, thus leading to a diversity of difluoromethylene compounds.     

Catalytic and highly stereoselective β-mannopyranosylation using a 2,6-lactone-bridged mannopyranosyl ortho-hexynylbenzoate as donor

An efficient and catalytic protocol for highly stereoselective construction of β-mannopyranosylation has been developed. Glycosylation of 2,6-lactone-bridged mannopyranosyl ortho-hexynylbenzoate with various acceptors proceeded smoothly in the presence of 5% Hg(II) at room temperature, resulting in the corresponding β-mannosides in high yield and exclusive β-stereoselectivity.     

In situ 19F NMR spectroscopy study of enzymatic transglycosylation reactions using α-d-aldohexopyranosyl fluorides as donors and acceptors

The use of ¹⁹F NMR spectroscopy to study the kinetics of the self-condensation reaction of α-d-aldohexopyranosyl fluorides catalysed by α-glycosidases is described. The corresponding fluorinated disaccharides thus synthesised present separate individual fluorine resonances allowing the integration of each species. This method looks particularly useful to help in the choice of donor in enzymatic transglycosylation reactions since the self-condensation reaction always remains in competition with the condensation reaction (reaction of the donor with acceptors other than itself).     

Catalytic, asymmetric, interrupted Feist-Bénary reactions of α-tosyloxyacetophenones

A new variant of the Interrupted Feist-Bénary (IFB) reaction uses α-tosyloxyacetophenones as electrophiles and proceeds in good yields and excellent enantioselectivities.     

Catalytic enantioselective electrophilic α-hydrazination of β-ketoesters using bifunctional organocatalysts

The catalytic enantioselective electrophilic α-hydrazination promoted by chiral bifunctional organocatalysts is described. Treatment of β-ketoesters with azodicarboxylates as electrophilic amination reagents under mild reaction conditions afforded the corresponding α-amino β-ketoesters with excellent enantiomeric excesses (93-99% ee).     

Synthesis of α-aminonitriles using silica-bonded N-propylpiperazine sulfamic acid as a recyclable catalyst

<正>α-Aminonitriles were synthesized via a one-pot three-component condensation of aldehydes,amines,and trimethylsilyl cyanide using silica-bonded N-propylpiperazine sulfamic acid(SBPPSA) as a recyclable solid acid at room temperature.SBPPSA showed much the same efficiency when used in consecutive reaction runs.