PMA-SiO_2 catalyzed synthesis of β-keto enol ethers

An efficient conversion of β-diketones into corresponding β-keto enol ethers with catalytic amount of PMA-SiO2 has been achieved.

Regioselective Addition of Silyl Enolates to α, β-Unsaturated Aldehyde and its Acetal Catalyzed by MgI2 Etherate

Regioselective addition reactions of silyl enolates to a, b-unsaturated aldehyde and its acetal catalyzed by MgI2 etherate give aldol adducts (1, 2-addition) preferentially over Michael adducts (1, 4-addition). This unique regioselectivity is distinctly different with other Lewis acidic promoters and may be attributed to the high oxyphilicity of IMg+.

Substituent, Temperature and Solvent Effects on the Keto-Enol EQUILIBRIUM in <i>&beta;</i>-Ketoamides: A Nuclear Magnetic Resonance Study

Substituent, temperature and solvent effects on tautomeric equilibria in several β-ketoamides have been investigated by means of nuclear magnetic resonance spectroscopy (NMR). Keto-enol equilibrium predominates over the amide-imidol one. The relative stability of the individual tautomers and the corresponding equilibrium shifts are explained considering electronic and steric effects and tautomer stabilization via internal hydrogen bonds. In solution, these compounds exist mainly as ketoamide and Z-enolamide tautomers, both presenting intramolecular hydrogen bonds.

Catalytic Asymmetric[3+2]Cycloaddition of Exocyclic Enol Ethers for the Synthesis of Spiroketals

An efficient synthesis of chiral benzannulated spiroketals via catalytic asymmetric[3+2]cycloaddition of exocyclic enol ethers with p-quinones was achieved.The transformation was enabled by a chiral N,N′-dioxides/Tm^(Ⅲ)complex as the Lewis acid catalyst and afforded a series of enantiomerically enriched benzannulated spiroketal derivatives in good yields(up to 99%)and enantioselectivities(up to 98%ee).Topographic steric maps and distribution of the buried volumes of the catalysts via Cavallo’s SambVca 2 tool were used to elucidate the enantioinduction raised by the ligands and the metal ions.

NiH-Catalyzed Reductive Hydrocarbonation of Enol Esters and Ethers

Chiral dialkyl carbinols and their derivatives are significant synthetic building blocks in organic chemistry and related fields.The development of convenient and efficient methods to access these compounds has long been an important endeavor.Herein,we report a NiH-catalyzed reductive hydroalkylation and hydroarylation of enol esters and ethers.α-Oxoalkyl organonickel species were generated in situ in a catalytic mode and then participated in cross-coupling with alkyl or aryl halides.This approach enabled C(sp^(3))–C(sp^(3))and C(sp^(3))–C(sp^(2))bond formation under mild reductive conditions with simple operations,thereby boosting a broad substrate scope and good functional compatibility.Esters of enantioenriched dialkyl carbinols were accessed in a catalytic asymmetric version.Mechanistic studies demonstrated that this reaction proceeded through a syn-addition of Ni–H intermediate to an enol ester with high regio-and enantioselectivity.

Acid Catalyzed Condensation of Phenylethanal Enol or Thiol Enol Ether to 2-Phenylnaphthalene

Treatment of enol ether or thiol enol ether of phenylethanals with sulfuric or polyphosphoric acid in toluene or xylene gave 2-phenylnaphthalene in good yield. More importantly, a one-pot reaction has been developed.

犬弓首蛔虫enol-1基因的克隆及序列分析

对犬弓首蛔虫烯醇化酶(enolase)基因(enol-1)进行克隆及序列分析,预测其作为抗犬弓首蛔虫疫苗候选抗原的潜力。从犬弓首蛔虫的cDNA中扩增出enol-1基因,连接至pMD18-T载体,并筛选阳性克隆后,测序鉴定。将测序结果正确的核苷酸序列翻译成氨基酸序列,运用生物信息学软件分析enol-1蛋白的结构,预测抗原表位及功能位点,并运用Maximum likelihood(ML)法构建了系统发育树。结果表明:enol-1基因长1 311 bp,可编码437个氨基酸。Enol-1蛋白中包含18个α-螺旋区,7个β-折叠区,10个亲水区域和16个柔性区域,并预测含有9个线性B细胞抗原表位,enol-1蛋白可能具有潜在的免疫原性。并对犬弓首蛔虫enol-1基因进行了克隆及序列分析,为评价enol-1蛋白作为犬弓首蛔虫亚单位疫苗及表位疫苗奠定了基础。

Light-triggered release of insecticidally active spirotetramat-enol

Spirotetramat metabolizes to its active enol form in the plant. We described here a photocaged pesticide delivery system that can release insecticidal spirotetramat enol form upon light irradiation. Covalently linking spirotetramat-enol with photoresponsive coumarin generated the caged insecticide. The photophysical and photochemical properties, deprotection photolysis and insecticidal activities of the caged spirotetramat enol were studied. This light-triggered system can undergo cleavage to release free spirotetramat enol form at the presence of blue light （420 nm） or sunlight, Bioassays indicated that the triggered molecule has no obvious insecticidal activity against Aphis craccivora Koch at dark and could be activated by light to release the insecticidal ingredients, which provides precise control over insecticide delivery.

Conversion of Carbonyl Compounds to Olefins via Enolate Intermediate

Summary of main observation and conclusion A general and efficient protocol to synthesize substituted olefins from carbonyl compounds via nickel catalyzed C-O activation of enolates was developed.Besides ketones,aldehydes were also suitable substrates for the presented catalytic system to produce di-or tri-substituted olefins.It is worth noting that this approach exhibited good tolerance to highly reactive tertiary alcohols,which could not survive in other reported routes for converting carbonyl compounds to olefins.This method also showed good regio-and stereo-selectivity for olefin products.Preliminary mechanistic studies indicated that the reaction was accomplished through nickel catalyzed C-O activation of enolates,thus offering helpful contribution to current enol chemistry.

芳构化法合成2,5-二羟基对苯二甲酸反应机理的密度泛函理论研究

采用密度泛函理论(DFT)计算,研究了由1,4-环己二酮-2,5-二甲酸二甲酯(DMSS)制备2,5-二羟基对苯二甲酸(DHTA)的反应机理.其中,采用IEFPCM溶剂模型着重计算了DMSS由酮式互变异构为烯醇式的溶剂效应,并探究了碘在催化DMSS烯醇式氧化芳构化过程中的作用机制.计算结果表明,在溶剂分子的辅助下,DMSS酮-烯醇式互变异构反应的能垒显著降低;芳构化过程中,碘首先与过氧化氢反应生成活性物质次碘酸,其催化DMSS烯醇式发生碘代反应,并经过后续的消去和互变异构生成2,5-二羟基对苯二甲酸二甲酯(DMDHT),DMDHT进一步水解生成DHTA.同时,通过核磁共振氢谱测试验证了DMSS酮-烯醇式互变异构的溶剂效应;反应性能考评实验结果表明,相较于无催化剂,在碘的催化作用下,DMDHT产品的纯度和收率更高.

Studies on the reactions of silyl enol ether with perfluoroorganic compounds——I. The reaction of silyl enol ether with perfluoroalkyl iodide

The reaction of silyl enol ethers (la-le) with perfluoroalkyl iodides (2f-2k) initiated with sodium dithionite was studied, α-Perfluoroalkyl ketones (3) were synthesized in excellent yield by this method, α,β-Unsaturated fluorinated ketones (4) were obtained easily by dehydrofluorination of the α-perfluoroalkyl ketones. A radical mechanism was proposed.

Analysis of keto-enol tautomers of curcumin by liquid chromatography/mass spectrometry

Keto-enol tautomers of curcumin were confirmed by reversed-phase liquid chromatography（RPLC）/ hybrid quadrupole ion trap/time-of-flight mass spectrometry（QIT/TOFMS）.Tautomers gave different MS/MS spectra in negative mode.Different mass spectra were also obtained by hydrogen/deuterium exchange LC/MS/MS in positive mode.Our results suggest that enol form is the major form in the solution（water/acetonitrile）.

Chiral N-phosphonyl imine chemistry:asymmetric additions of glycine enolate to diphenyl diamine-based phosphonyl imines

Diphenyl diamine-based phosphonyl imines attached by the N-isopropyl group in the auxiliary have been synthesized in good yields under convenient reaction conditions.These new chiral N-phosphonyl imines can react with glycine enolate smoothly to give chiral α-β diamino esters in good yields(72%-90%) and up to excellent diastereoselectivity(>99:1 dr).By treatment with HBr,the chiral auxiliary can be readily removed.The absolute structure has been unambiguously determined by converting a product to a known sample.

Radical cation salts induced domino reaction of anilines with enol ethers:Synthesis of 1,2,3,4-tetrahydroquinoline derivatives

A domino reaction of anilines with cyclic and acyclic enol ethers induced by catalytic amounts of TBPA^（·＋）（5 mol%） was investigated and a series of 2,4-disubstituted-1,2,3,4-tetrahydroquinolines were synthesized.Different from cyclic enol ethers, when acyclic enol ethers were used in the reaction,they serve as surrogates of acetaldehyde,producing a series of 2-methyl-4- anilino-1,2,3,4-tetrahydroquinolines.A single electron transfer mechanism was proposed to rationalize the products formation.

(E) Enol ethers from the stereoselective reduction of α-alkoxy-β-ketophosphonates and Wittig type reaction

When α-alkoxy-β-ketophosphonates,prepared by the Rh(Ⅱ) mediated insertion reaction of α-diazo-β-ketophosphonates into the OH bond of primary alcohols,were reduced either by NaBH4 in the presence of CaCl2 or by DIBAL,they respectively gave the corresponding anti or syn stereomeric hydroxyphosphonates with pronounced to complete stereoselectivity.Submitted to the action of potassium tert-butoxyde,syn isomers led to the corresponding pure(E) enol ethers in moderate to good yields.Under the same conditions anti isomers led to a mixture of(Z) and(E) enol ethers in rather poor yields.The sequence was applied to the preparation of some allyl-vinyl ethers with a(E) configuration for the vinylic double bond.

BiX3 and FeX3-Promoted Prins Cyclization of Enol Ethers in CH2Cl2

The Prins cyclization of enol ethers has been realized by employing BiX3 （or FeX3） as catalyst and TMSX （X = Br, C1） as the halogen source. The presence of a tiny amount of water in the solvent dichloromethane played a key role for the reaction to proceed. The reaction is believed to be catalyzed by Lewis acid-assisted Bronsted acids, which were generated in situ from MX3 and water in the solvent.

Regio-and Diasteroselective C-Silylation of Enolate Enabled by a β-Boronyl Group

Silyl enol ethers are often obtained when the lithium enolates are trapped with chlorosilanes.Herein,we report a general method for the regio-and diasteroselective C-silylation of enolate enabled by theβ-boronyl group.The formation of five-membered chelation intermediate is key to the C-selective silylation and anti-selectivity.The operationally simple protocol provides a general and predictable access to theα-silylated esters.The synthetic versatility of the boron-silicon bifunctional products was demonstrated by down-stream transformations.