REDUCTION BY HYPOPHOSPHOROUS ACID IN ORGANIC SYNTHESIS

Hypophosphorous acid and its salt were found to serve as a new agent for selective reduction of α,β-unsaturated carbonyl compounds under mild reaction conditions.     

Copper-Catalyzed Enantioselective Synthesis of α-Hydroxyamine Using Monodentate Phosphoramidites

Development of new methods for the introduction of a nitrogen atom to a carbonyl group is still the most important synthetic target. Cu-catalyzed addition of organozinc reagents to α,β-unsaturated carbonyl compounds has been the subject of intensive investigation.[1] Moreover, trapping of the intermediate Zn-enolates has been achieved using nitrosobenzene. To demonstrate the feasibility of developing enantioselective variants of these tandem C-C bond formations,α,β-unsaturated substrates a～d was subjected to standard reaction conditions using Feringa's (L1*, L2*) and our own phosphoramidite ligands (L3*, L4*). In this reaction, medium to high levels of enantioselectivities were observed.     

Regioselective 1,2-Addition of Ti(IV)-enolate to α, β–Unsaturated Compounds

The nucleophilic addition to α, β-unsaturated carbonyl compounds is a fundamental C-C bond forming reaction in organic chemistry1. Since there are two reaction sites in the α, β–unsaturated carbonyl group, the regioselectivity of the nucleophilic addition (1, 2 vs. 1, 4 addition) is of primary importance when applying this type of reaction in organic synthesis. Factors that control the regioselectivity include the softness and hardness of the attacking nucleophiles2, solvent and temperatu…     

Studies on the cyclization reaction of D-aspartic acid

The cyclization reaction of D-aspartic acid was studied, the carboxyl groups of D-aspartic acid were protected by benzyl alcohol to give compound D-dibenzyl aspartate. Then (4R)-benzyl azetidine-2-one-4-carboxylate and meso-3,6-disubstituted piperazine- 2,5-diones were synthesized via intramolecular cyclization and intermolecular cyclization of D-dibenzyl aspartate, respectively, and their structures were confirmed by 1H NMR and MS. Both cyclization reaction conditions were also investigated in detail.     

Application of organic selenides and tellurides in organic synthesis

This paper describes the progress on the synthesis of organic selenides and tellurides and their application in organic synthesis.Low valent selenium and telluronium compounds having high reducing selectivity can be used to form carbon-hydrogen bonds as special reducing reagents.Telluronium ylides can react with aldehydes and ketones by Wittig-type condensation to produce (E)-configuration alkenes stereoselectively.α-Phenylselanyl arsonium ylides were prepared by transyl-idation reaction of arsonium ylides with phenylselanyl halides which can undergo Wittig-type reactions with carbonyl compounds to give (Z)-α-selanyl-α,β-unsaturated compounds with high stereoselectiv-ity.Zirconium,tin,boron,halogen,metal or hetero-atom were introduced in organoselenium and telluronium compounds as new difunctional group reagents.Under transition metal catalysis,the corresponding cross coupling reactions provide new methods of formation of carbon-carbon double bonds,which were used in the stereoselective synthesis of     

Preparation and Reactions of Amino Acid Ester Sulfones as New Remote Asymmetrical Induced Reagents

The development of chiral auxiliary-controlled asymmetric synthesis has been receiving increasing interest in recent yearsfi,2] Various chiral auxiliary reagents have been observed[3] and a lot of results showed that variation of the chiral auxiliary could influence asymmetric induction. Recently, it has been reported the reaction of the aminated sulfones as a remote chiral auxiliary with α,β-unsaturated carbonyl compounds.[4] Here we would like to report the preparation of amino acid ester sulfones as new remote asymmetrical induced reagents and their reactions with α,β-unsaturated esters.     

Michael Additiion of Alkyl Amine to α,β-Unsaturated Carbonyl Compounds Catalyzed by KF／Al2O3

The β-aminocarboxylic acid derivatives were synthesized by Michael addition reaction ofalkyl amine and α,β-unsaturated carbonyl compounds in the presence of potassium fluoride onalumina.     

Chromium-catalyzed asymmetric synthesis of 1, 3-diols

An efficient,chromium-catalyzed highly enantioselective preparation of protected 1,3-diols has been achieved.In the presence of a chiral chromium catalyst using the carbazole-based bisoxazoline as the chiral ligand,a variety of optically pure 1,3-diols were synthesized in 34%-87%yields with up to 98%ee.The benzyl as well as silyl ethers were suitable substitutions for the hydroxyl group.Meanwhile,aromatic,aliphatic and α,β-unsaturated aldehydes are well tolerated under the mild reaction conditions.     

[Bmim]OAc Catalyzed Michael Addition of Active Methylene to α,β-Unsaturated Carboxylic Esters and Nitriles

<正>Michael addition of active methylene compounds toα,β-unsaturated carboxylic esters and nitriles was effectively catalyzed by a basic ionic liquid,1-butyl-3-methylimidazolium acetate([Bmim]OAc).The bis-addition products were selectively obtained in high yields under miLd reaction conditions.     

An Efficient Method for α-Alkylation of γ-Butyrolactone

Alkylated lactone is a common structure and segment in many natural products and medicines. The examples of alkylating lactone system at -position, obtained by reaction with alkyl halide such as MeI, in the presence of strong base LDA or it抯 derivatives, are very few1a, 1b. When this method was applied to the aromatic compound, the self-condensation of g-butyrolactone could not be avoided. In our previous work we have reported the hydrogenation of ? -unsaturated carbonyl compounds by cat…     

镍铁氰化物纳米粒子的合成及其多相催化无溶剂条件下苯甲醇氧化的潜能(英文)

Nickel hexacyanoferrate nanoparticles were synthesized and characterized using elemental analysis, thermal analysis, infrared spectroscopy, and X-ray diffraction. A FE-SEM image of the nickel hexacyanoferrate showed that it consists of nearly spherical particles with sizes ranging from 30 to 70 nm. The synthesized material was found to be a heterogeneous catalyst useful for the solvent-free oxidation of benzyl alcohol with H2O2 as an oxidant. A 36% conversion of benzyl alcohol to benzaldehyde was achieved under optimized reaction conditions using specific parameters such as the amount of catalyst, the temperature, the benzyl alcohol to H2O2 molar ratio, and the reaction time.     

Knoevenagel condensation of α,βunsaturated aromatic aldehydes with barbituric acid under non-catalytic and solvent-free conditions

An efficient route for the synthesis of 5-(arylpropenylidine)-2,4,6-pyrimidinetrione 3 from an appropriateα,β-unsaturated aromatic aldehydes 1 and barbituric acid 2 under both non-catalytic and solvent-free microwave irradiation conditions was described.In this way,a range of biologically important compounds 3 was obtained in good to excellent yields (86-98%) in a very short reaction time (30-80s).     

SnCl2／Cu-Mediated Carbonyl Allylation Reaction in Water： Scope, Selectivity and Mechanism

Copper was found to be able to promote the SnC12-mediated carbonyl allylation reactions in water, giving the corresponding homoallylic alcohol products in very high yields. Detailed studies showed that the reaction could be applied to a variety of carbonyl compounds including those with hydroxyl, amino and nitro groups. It was also found that this reaction showed good regioselectivities for some substrates. Furthermore, carefully controled experiments and in situ NMR measurements provided important insights into the mechanism of the newly developed reaction.     

Novel Stereoselective Synthesis of (E)- α，β-Unsaturated Esters by the Tandem Reaction of Deprotonation-Oxidation-Wittig Reaction from Phosphonium and Arsonium Salt

Phosphonium or arsonium salt 1 can undergo the tandem reaction of deprotonation -oxidation-Wittig reaction with alcohol 2 in the presence of sodium hydroxide and manganese dioxide,which affords a general simplified method for the stereoselective synthesis of (E)- α-β-unsaturated esters 3.     

α,α-二乙酰基二硫缩烯酮与α,β-不饱和酮的加成反应研究

α,α-diacetyl ketene thioacetals had been investigated as odorless thiol equivalents in thia-Michael addition reaction.Under solvent-free conditions,a series of reactions between α,α-diacetyl ketene thioacetals and α,β-unsaturated ketones were carried out promoting by concentrated hydrochloric acid.The corresponding thia-Michael adducts in high yields were obtained.Furthermore,a mechanism for this thia-Michael addition reaction was proposed preliminary.     

A novel hydrogen peroxide-initiated reaction of difluorodiiodomethane with alkynes

The reaction of difluorodiiodomethane with alkynes (4a-e) in the presence of hydrogen peroxide afforded the corresponding β-iodo-α,β-unsaturated carboxylic acids.When propargylic alcohol was used as the substrate,β-iodo-α,β-unsaturated γ-butyrolactone (5f) was produced.The mechanism of the reaction was suggested.     

A clean and efficient cyclocondensation to pyrido[2,3-d]pyrimidine derivatives in aqueous media

A series of pyrido[2,3-d]pyrimidine derivatives were easily constructed by cyclocondensation reactions of 6-aminouracils or 6- aminothiouracil withα,β-unsaturated carbonyl compounds（aldehyde,ketone and ester） possessing a leaving group on theβposition,in H₂O under reflux conditions.     

Asymmetric annulations based on cycloisomerization of cyclopropyl tethered allenyl ketones by bimetallic relay catalysis

The diastereo-and enantioselective tandem cycloisomerization/[4 + 2]-cycloaddition reaction of cyclopropyl tethered allenyl ketones with α,β-unsaturated carbonyl compounds was realized firstly under mild reaction conditions by using bimetallic silver(I)/chiral metal-N,N′-dioxide catalysts, providing a facile and atom-economic route to enantioenriched polysubstituted furopyran derivatives with good results. Possible transition state models were proposed to explain the stereoinduction.     

A mild,simple and efficient method for selectiveα-monobromination of 1,3-diketones and β-ketoesters using pyridinium bromochromate

Pyridinium bromochromate has been found to be a highly efficient and selective reagent for theα-monobromination of 1,3-diketones andβ-keto-esters in the absence of base,Lewis acid,or other catalyst.The products were formed in high to excellent yields under mild reaction conditions and in short reaction times.     

A simple and convenient method for direct α-chlorination of ketones with ammonium chloride and Oxone~

When ketones were treated with ammonium chloride and Oxone~ in MeOH at room temperature,a directα-chlorination of ketones was occurred and a series of the corresponding a-chloroketones were obtained in moderate to good yields after 24 h.In this reaction,ammonium chloride was used as the source of chlorine and Oxone~ was used as an oxidant.This method was simple, convenient and providing a novel procedure for preparation of a-chloroketones.