Chiral 2,6-bis(oxazolinyl)pyridine-rare earth metal complexes as catalysts for highly enantioselective 1,3-dipolar cycloaddition reactions of 2-benzopyrylium-4-olates

Significant levels of enantioselectivity were obtained in 1,3-dipolar cycloadditions of 2-benzopyrylium-4-olate generated from the Rh(2)(OAc)(4)-catalyzed decomposition of o-methoxycarbonyl-alpha-diazoacetophenone. This reaction utilized chiral 2,6-bis(oxazolinyl)pyridine (Pybox)--rare earth metal triflate complexes as chiral Lewis acid catalysts. The reactions with several benzyloxyacetaldehyde derivatives catalyzed by a Sc(III)--Pybox-i-Pr complex (10 mol %) proceeded smoothly to yield endo-adducts selectively with high enantioselectivity (up to 93% ee). For the reaction with benzyl pyruvate, the Sc(III)-Pybox-i-Pr complex (10 mol %) catalyzed the reaction effectively in the presence of trifluoroacetic acid (10 mol %) to yield an exo-adduct with both high diastereo- and enantioselectivity (94% ee). This catalytic system was efficiently applied to the reactions with several other alpha-keto esters with high exo- and enantioselectivities (up to 95% ee). In contrast to the reaction with carbonyl compounds, Yb(III)--Pybox-Ph complex (10 mol %) was found to be effective to obtain high enantioselectivity (96% ee) of diastereoselectively produced exo-cycloadduct in the reaction with 3-acryloyl-2-oxazolidinone.     

硫酸钙晶须催化合成三羟甲基丙烷三丙烯酸酯

以三羟甲基丙烷(TMP)、丙烯酸(AA)为原料,硫酸钙晶须为催化剂,环己烷和甲苯混合物为带水剂,合成三羟甲基丙烷三丙烯酸酯(TMPTA).考察了原料配比、催化剂用量等因素对产品酯化率的影响.结果表明:以对苯二酚和吩噻嗪做混合阻聚剂,n(AA)∶n(TMP)=3.40,硫酸钙晶须的质量分数(以三羟甲基丙烷用量为基准)为2.0%,、环己烷用量20%、甲苯用量30%;酯化反应温度为98 ℃,反应时间为5 h,在此条件下合成的三羟甲基丙烷三丙烯酸酯酯化率大于96.8%,纯度达到97.6%.     

Proline-based Amino Pyridine Dipeptides as Efficient Organocatalysts for Direct Aldol Reaction

A series of proline-based amino pyridine dipeptide organocatalysts was synthesized and applied in direct asymmetric intermolecular aldol reaction. These catalysts showed good solubility in organic solvents, good yields (73%―97%) and enantioselectivitives(74%―94%). Among them, dipeptide organocatalyst(2) was found to be the most efficient one for the asymmetric aldol reaction between cyclohexanone and 4-nitrobeznaldehyde. After optimizing the catalytic reaction conditions, we found that the catalyst showed high yield(97%), enantioselectivity(e.e., up to 92%) and anti-diastereoselectivity(up to 95:5) at mild room temperature without any additives.     

CuOTf/NNN三齿钳形配体催化不对称Henry反应

以(R)-BINOL为原料合成NNN三齿钳形手性配体,研究了其与各种金属盐形成金属络合物在室温下原位催化芳香醛与硝基甲烷的不对称Henry反应.考察了不同金属盐、溶剂、碱对反应的影响,优化得到最佳反应条件为:CuOTf/NNN三齿配体(1∶1)催化体系,催化剂用量为10 mol%,甲醇作溶剂,室温反应5 d,收率57%,对映选择性80%ee;加入10 mol%有机碱(Me3Si)2MeN后反应速度加快,对映选择性略有降低,室温反应17 h,收率37%,ee值67%.此催化体系适用于大部分的芳香醛,收率中等,对映选择性可达75%ee.     

Asymmetric catalysis in a micro reactor—Ce, Yb and Lu catalysed enantioselective addition of trimethylsilyl cyanide to benzaldehyde

A T-shaped micro reactor was used for the optimisation of reaction conditions for the enantioselective silylcyanation of benzaldehyde catalysed by lanthanide-pybox complexes. Compared to a conventional batch procedure, higher conversion was observed within shorter reaction time. The micro reactor process involving Lu(III) afforded essentially the same enantioselectivity as the batch process (73 vs 76% ee), whereas the enantioselectivity was lower in the micro reactor for catalysts containing Yb(III) (53 compared to 72%). Ce(III) provided very low selectivity in both types of processes (1 and 11% ee, respectively). A study of the effect of additives showed that the enantioselectivity in the Yb catalysed reaction performed in the micro reactor could be increased to 66%, whereas only a minor improvement, to 78% ee, was observed in the reaction with Lu.     

Rapid conversion of cellulose to 5-hydroxymethylfurfural using single and combined metal chloride catalysts in ionic liquid

Direct conversion of cellulose into 5-hydroxymethylfurfural(HMF) was performed by using single or combined metal chloride catalysts in 1-ethyl-3-methylimidazolium chloride(Cl) ionic liquid.Our study demonstrated formation of 2-furyl hydroxymethyl ketone(FHMK),and furfural(FF) simultaneously with the formation of HMF.Various reaction parameters were addressed to optimize yields of furan derivatives produced from cellulose by varying reaction temperature,time,and the type of metal chloride catalyst.Catalytic reaction by using FeCl3 resulted in 59.9% total yield of furan derivatives(HMF,FHMK,and FF) from cellulose.CrCl3 was the most effective catalyst for selective conversion of cellulose into HMF(35.6%) with less concentrations of FHMK,and FF.Improving the yields of furans produced from cellulose could be achieved via reactions catalyzed by different combinations of two metal chlorides.Further optimization was carried out to produce total furans yield 75.9% by using FeCl3/CuCl2 combination.CrCl3/CuCl2 was the most selective combination to convert cellulose into HMF(39.9%) with total yield(63.8%) of furans produced from the reaction.The temperature and time of the catalytic reaction played an important role in cellulose conversion,and the yields of products.Increasing the reaction temperature could enhance the cellulose conversion and HMF yield for short reaction time intervals(5~20 min).     

β-Homoamino acids as catalysts in enantioselective intra- and intermolecular aldol reactions

β³-Homoamino acids catalyze the intra- (cf. the Hajos-Parrish-Eder-Sauer-Wiechert reaction) as well as the intermolecular aldol reaction. The stereochemical outcome with selectivities of up to 83% ee is reversed in the intramolecular reaction, when we go from the proteinogenic amino acids to the homologues, and reaction time increases dramatically for both reactions. In contrast, in the intermolecular reaction Me-β³hPhe-OH gives the same enantiomer as (S)-proline does, but with lower enantiomeric excess (54% vs 48% ee).     

Gas-phase Reaction of 2-Chlorothiophene with Hydrogen Sulfide in the Presence of Alcohols

The effect of methanol and ethanol on the route of the gas-phase reaction of 2-chlorothiophene with hydrogen sulfide, leading to 2-thiophenethiol and to bis(2-thienyl) sulfide, has been investigated. It was found that methanol significantly enhances this reaction and increases its selectivity for the thiol at higher temperatures than without the initiator. The optimal conditions were achieved at 570°C in the presence of 10 mole % of methanol when the conversion of the 2-chlorothiophene in the reaction with hydrogen sulfide reaches 98% and the yield of the thiophenethiol (43%) exceeds that of the bis(2-thienyl)sulfide (31%). In the absence of methanol the 2-thiophenethiol is formed only at 510-540°C in just 17% yield, the basic reaction product being the indicated sulfide (52% yield); the conversion of the 2-chlorothiophene does not exceed 54%.     

Catalytic Systems Containing p-Toluenesulfonic Acid for the Coupling Reaction of Formaldehyde and Methyl Formate

The coupling reaction of formaldehyde(FA)and methyl formate(MF)to form methyl glycolate(MG)and methyl methoxy acetate(MMAc),catalyzed by p-toluenesulfonic acid(p-TsOH)as well as assisted by different kinds of solvents or Ni-containing compounds,had been investigated.The results showed that when the reaction was carried out at 140℃,with a molar ratio of FA to MF of 0.65:1, molar fraction of p-TsOH to total feedstock of 11.0%,and reaction time of 3 h,the yield of MG and MMAc was 31.1% and 17.1%,respectively,p-TsOH catalyzed the coupling reaction by means of the synergistic catalysis of protonic acidity and soft basicity.Adding extra solvents to the reaction system was unfavorable for the reaction.The composite catalytic system consisting of p-TsOH and NiX_2(X=Cl,Br,I)exhibited a high catalytic performance for the coupling reaction,and NiX_2 acted as a promoter in the reaction,whose promotion for the catalysis increased in the following order:NiCl_2相似文献   

The Lewis acid-catalyzed nazarov reaction of 2-(n-methoxycarbonylamino)-1,4-pentadien-3-ones

[reaction: see text] A highly efficient carbonylative Suzuki-Miyaura coupling reaction of lactam-derived vinyl triflates and alkenylboronic acids afforded 2-(N-methoxycarbonylamino)-1,4-pentadien-3-ones as suitable substrates for the Nazarov reaction. The most competent Lewis acids for the Nazarov reaction were Cu(OTf)(2) (2 mol %) and Sc(OTf)(3) (3 mol %) in DCE, which provided the Nazarov products in excellent yield. As both the carbonylative coupling and the subsequent Nazarov reaction were high yielding, the overall methodology is a concise and efficient route to [1]pyrindine systems.     

Diels-Alder reaction of maldoxin with an isopropenylallene

The Diels-Alder reaction of maldoxin with an isopropenylallene at 60-75 °C afforded an adduct closely related to chloropestolide A (24%) and a second adduct (0-11%) that underwent an ene reaction to generate the chloropupukeanolide D (11-22%) skeleton. The Diels-Alder reaction occurred with good selectively (>5:1) from a single face of maldoxin under much milder conditions than previously reported for the analogous dimethoxycyclohexadienone. Furthermore, the ene reaction took place under mild conditions, whereas the analogous Diels-Alder adduct from the dimethoxycyclohexadienone did not undergo an ene reaction.     

A hierarchically zeolite Y for the N-heterocyclic compounds synthesis

High activity and selectivity of the hierarchical H-Ymmm zeolite in the synthesis of practically important pyridines (by interaction of C₂–C₄ alcohols with formaldehyde and ammonia, cyclocondensation of acetaldehyde and propanal with ammonia), dialkyl quinolines (by reaction of aniline with aldehydes) and alkyl dihydroquinolines (by reaction of aniline with ketones- acetone, acetophenone) were revealed in the research.The advantages of the micro-meso-macroporous H-Ymmm zeolite over the microporous H-Y zeolite in the synthesis of pyridines and quinolines were demonstrated. In the products formed by the reaction of ethanol with formaldehyde and ammonia, picolines (up to 63%) and lutidine are predominant in H-Ymmm, Pb-H-Ymmm and Fe-H-Ymmm zeolites. The interaction of n-propanol (n-butanol) with formaldehyde and ammonia in the presence of H-Ymmm zeolite with high selectivity produced 3,5-lutidine (up to 90%) or 3,5-diethylpyridine (85%). H-Ymmm zeolite makes it possible to prepare 2-methyl-5-ethylpyridine with 87% selectivity (reaction of acetaldehyde with ammonia) and 2-ethyl-3,5-dimethylpyridine with 58% selectivity (reaction of propanal with ammonia).The synthesis of dialkylquinolines and dialkyltetrahydroquinolines with a total selectivity of 65–73% by the interaction of aniline with C₃–C₅ aldehydes has been carried out. The dihydroquinoline derivatives with the selectivity of up to 70% have been synthesized by the reaction of aniline with ketones (acetone, acetophenone).     

FeCl3作用下的碘代醚化反应: 一种合成碘代环烯醚的方便方法

对FeCl₃作用下各种炔醇与碘的反应进行了详细研究, 结果表明在FeCl₃和碘的作用下, 炔醇发生分子内碘代环化反应生成碘代环烯醚, 产率为63%～90%. 在相同的反应条件下, 炔丙醇类则生成邻二碘化物, 产率为15%～88%. 该反应具有操作简单、底物适应广、反应快(3 h)和碘用量(0.5 equiv.)少等特点, 是制备碘代环烯醚和2,3-二碘代烯醇的好方法.     

Partial oxidation of 4-tert-butyltoluene catalyzed by homogeneous cobalt and cerium acetate catalysts in the Br-/H2O2/acetic acid system: insights into selectivity and mechanism

The partial oxidation of 4-tert-butyltoluene to 4-tert-butylbenzaldehyde by hydrogen peroxide in glacial acetic acid, catalyzed by bromide ions in combination with cobalt(II) acetate or cerium(III) acetate, has been studied in detail. Based on the observed differences in reaction rates and product distributions for the different catalysts, a reaction mechanism involving two independent pathways is proposed. After the initial formation of a benzylic radical species, either oxidation of this intermediate by the metal catalyst or reaction with bromine generated in situ occurs, depending on which catalyst is used. The first pathway leads to the exclusive formation of 4-tert-butylbenzaldehyde, whereas reaction of the radical intermediate with bromine leads to formation of the observed side products 4-tert-butylbenzyl bromide and its hydrolysis and solvolysis products 4-tert-butylbenzyl alcohol and 4-tert-butylbenzyl acetate, respectively. The cobalt(II) catalysts Co(OAc)(2) and Co(acac)(2) are able to quickly oxidize the radical intermediate, thereby largely preventing the bromination reaction (i.e., side-product formation) from occurring, and yield the aldehyde product with 75-80 % selectivity. In contrast, the cerium catalyst studied here exhibits an aldehyde selectivity of around 50 % due to the competing bromination reaction. Addition of extra hydrogen peroxide leads to an increased product yield of 72 % (cerium(III) acetate) or 58 % (cobalt(II) acetate). Product inhibition and the presence of increasing amounts of water in the reaction mixture do not play a role in the observed low incremental yields.     

Porphyrins in Diels-Alder reactions. Improvements on the synthesis of barrelene-fused chlorins using microwave irradiation

The microwave irradiation technique was applied to the Diels-Alder reaction of tetrakis(pentafluorophenyl)porphyrin with pentacene and naphthacene. Both reactions proceed within minutes to afford the corresponding monoadducts in 83% and 23% yield, respectively. When compared with the yields obtained under classical heating (22% and no reaction, respectively), this represents an impressive improvement of these reactions. Bisadducts (bacteriochlorins and isobacteriochlorins) are also obtained in the reaction with pentacene; these compounds are not formed under classical heating.     

Asymmetric Morita-Baylis-Hillman reactions catalyzed by chiral Brønsted acids

Chiral BINOL-derived Br?nsted acids catalyze the enantioselective asymmetric Morita-Baylis-Hillman (MBH) reaction of cyclohexenone with aldehydes. The asymmetric MBH reaction requires 2-20 mol % of the chiral Br?nsted acid 2e or 2f and triethylphosphine as the nucleophilic promoter. The reaction products are obtained in good yields (39-88%) and high enantioselectivities (67-96% ee). The Br?nsted-acid-catalyzed reaction is the first example of a highly enantioselective asymmetric MBH reaction of cyclohexenone with aldehydes.     

Spontaneous hydrolysis reactions of cis- and trans-beta-methyl-4-methoxystyrene oxides (Anethole oxides): buildup of trans-anethole oxide as an intermediate in the spontaneous reaction of cis-anethole oxide

Rates and products of the reactions of trans- and cis-beta-methyl-4-methoxystyrene oxides (1 and 2) (anethole oxides) and beta,beta-dimethyl-4-methoxystyrene oxide (3) in water solutions in the pH range 4-12 have been determined. In the pH range ca. 8-12, each of these epoxides reacts by a spontaneous reaction. The spontaneous reaction of trans-anethole oxide (1) yields ca. 40% of (4-methoxyphenyl)acetone and 60% of 1-(4-methoxyphenyl)-1, 2-propanediols (erythro:threo ratio ca. 3:1). The spontaneous reaction of cis-anethole oxide is more complicated. The yields of diol and ketone products vary with pH in the pH range 8-11, even though there is not a corresponding change in rate. These results are interpreted by a mechanism in which 2 undergoes isomerization in part to the more reactive trans-anethole oxide (1), which subsequently reacts by acid-catalyzed and/or spontaneous reactions, depending on the pH, to yield diol and ketone products. The buildup of the intermediate trans-anethole oxide in the spontaneous reaction of cis-anethole oxide was detected by (1)H NMR analysis of the reaction mixture. Other primary products of the spontaneous reaction of 2 are (4-methoxyphenyl)acetone (73%) and threo-1-(4-methoxyphenyl)-1,2-propanediol (ca. 3%). The rates and products of the spontaneous reaction of 2 and its beta-deuterium-labeled derivative were determined, and the lack of significant kinetic and partitioning deuterium isotope effects indicates that the isomerization of 2 to ketone and to trans-anethole oxide must occur primarily by nonintersecting reaction pathways.     

Palladium-catalyzed allylation of imines with allyl alcohols

A catalytic system, Pd(OAc)2 (10 mol %)-P(n-Bu)3 (20 mol %)-Et3B (360 mol %), promotes allylic alcohols to undergo the allylation of anisidine-imines of aromatic and aliphatic aldehydes and furnishes homoallylamines in good to moderate yields. The reaction shows unique stereoselectivity, giving anti-isomers selectively. [reaction: see text]     

Chiral 1,1'-binaphthyl-2,2'-diammonium salt catalysts for the enantioselective Diels-Alder reaction with alpha-acyloxyacroleins

[reaction: see text] A diammonium salt of chiral 1,1'-binaphthyl-2,2'-diamine and trifluoromethanesulfonimide (Tf(2)NH) shows excellent catalytic activity and enantioselectivity for the Diels-Alder reaction of alpha-acyloxyacroleins with cyclic dienes. For example, in the presence of 5 mol % of the ammonium catalyst, the Diels-Alder reaction of alpha-(cyclohexanecarbonyloxy)acrolein with cyclopentadiene proceeded in EtCN at -75 degrees C to give the adducts in 88% yield with 92% exo and 91% ee. This catalyst can be easily prepared in situ by mixing the commercially available chiral diamine and Tf(2)NH.     

Products of the gas-phase reactions of OH radicals with (C2H5O)2P(S)CH3 and (C2H5O)3PS

Products of the gas-phase reactions of OH radicals with O,O-diethyl methylphosphonothioate [(C2H5O)2P(S)CH3, DEMPT] and O,O,O-triethyl phosphorothioate [(C2H5O)3PS, TEPT] have been investigated at room temperature and atmospheric pressure of air using in situ atmospheric pressure ionization mass spectrometry (API-MS) and, for the TEPT reaction, gas chromatography and in situ Fourier transform infrared (FT-IR) spectroscopy. Combined with products quantified previously by gas chromatography, the products observed were: from the DEMPT reaction, (C2H5O)2P(O)CH3 (21+/-4% yield) and C2H5OP(S)(CH3)OH or C2H5OP(O)(CH3)SH (presumed to be C2H5OP(O)(CH3)SH by analogy with the TEPT reaction); and from the TEPT reaction, (C2H5O)3PO (54-62% yield), SO2 (67+/-10% yield), CH3CHO (22-40% yield) and, tentatively, (C2H5O)2P(O)SH. The FT-IR analyses showed that the formation yields of HCHO, CO, CO2, peroxyacetyl nitrate [CH3C(O)OONO2], organic nitrates, and acetates from the TEPT reaction were <5%, 3+/-1%, <7%, <2%, 5+/-3%, and 3+/-2%, respectively. Possible reaction mechanisms are discussed.