Zhen-Yuan Xu

In situ enamine activation in aqueous salt solutions: highly efficient asymmetric organocatalytic Diels-Alder reaction of cyclohexenones with nitroolefins.

Deep-sea Diels-Alder: The asymmetric organocatalytic Diels-Alder reaction of cyclohexenones with aromatic nitroolefins can be carried out in seawater and brine. The reaction proceeds by an in situ enamine activation involving a one-step concerted addition pathway (see scheme).

Fischer indole synthesis catalyzed by novel SO3H-functionalized ionic liquids in water

Novel SO3H-functionalized ionic liquids bearing two alkyl sulfonic acid groups in the imidazolium cations were designed and successfully applied as catalysts for the one-pot Fischer indole synthesis in water medium. The sequence of the catalytic activity observed in the transformation was in good agreement with the Bronsted acidity order determined by the Hammett method. Various types of indoles from single-carbonyl ketones/aldehydes and cyclohexandiones were provided in 68–96% yields using the catalytic system of [(HSO3-p)2im][HSO4]/H2O. The indole products could be conveniently separated from the reaction mixture by filtration and the dissolved catalyst could be regenerated by treatment with a strongly acidic cation exchange resin, which meant the whole process was performed in water without using any organic solvents.

Mild and Versatile Nitrate-Promoted CH Bond Fluorination†

A novel and facile C-H bond fluorination proceeds under remarkably mild conditions (close to room temperature in most cases). Both aromatic and olefinic C(sp(2))-H bonds with a wide range of electronic properties are selectively fluorinated in the presence of a catalytic amount of simple, cheap, and nontoxic nitrate as the promoter. A Pd(II)/Pd(IV) catalytic cycle that is initiated by an in situ generated cationic [Pd(NO3)](+) species was proposed based on preliminary mechanistic studies.

Erlenmeyer Synthesis for Azlactones Catalyzed by Ytterbium(III) Triflate under Solvent‐Free Conditions

Abstract A series of 4‐arylidene‐2‐phenyl‐5(4)‐oxazolones were synthesized from cyclodehydration–condensation of hippuric acid, aromatic aldehydes, and acetic anhydride catalyzed by ytterbium(III) triflate under mild conditions in excellent yields.

Highly Efficient AILs/L‐Proline Synergistic Catalyzed Three‐Component Asymmetric Mannich Reaction

Abstract A three‐component asymmetric Mannich reaction of isovaleraldehyde, methyl ketones, and aromatic amines was efficiently synergistic catalyzed by amide‐task‐specific ionic liquids (AILs)/L‐proline under mild conditions. The corresponding asymmetric Mannich reaction adducts were obtained in moderate to high yields and stereo selectivity in all the cases tested. The product was easily isolated, and the remaining catalysis system can be readily recovered and reused at least three times without significant loss of catalytic activity and selectivity.

Facile and efficient one-pot synthesis of 2-arylbenzoxazoles using hydrogen tetrachloroaurate as catalyst under oxygen atmosphere

In this paper, we presented a novel method for the facile and efficient one-pot synthesis of 2-arylbenzoxazoles, which were directly synthesized from 2-aminophenol and aldehydes catalyzed by hydrogen tetrachloroaurate (HAuCl4·4H2O) under an oxygen atmosphere with anhydrous tetrahydrofuran (THF) as solvent or in solvent-free condition. The results show that this method could bring excellent yields as high as 96%. THF was proven to be the best choice among several solvents screened and the reaction was tolerated with a variety of aromatic aldehydes possessing electron-donating or withdrawing groups. The advantages of the present method lie in catalytic process using economic and environmentally benign dioxygen as oxidant.

Oxidative Aromatization of 1,3,5-Trisubstituted Pyrazolines Using Hydrogen Tetrachloroaurate as Catalyst Under an Oxygen Atmosphere

Today gold is without a doubt the “star metal” in chemistry because of the focus of attention on gold-catalyzed organic transformations in recent years.1–7 Among various new transformations catalyzed by gold, those involving nucleophilic additions to C-C multiple bonds (alkynes, alkenes or allenes)8–10 and catalytic C-H bond functionalization11,12, have been studied intensively. In contrast, gold-catalyzed oxidation chemistry, in particular gold as heterogeneous and/or homogeneous catalyst for selective oxidation reactions with economic and environmentally benign oxidants, such as dioxygen or hydrogen peroxide, has been less developed.13 Thus far, representative oxidation transformations are mainly limited in oxidation of monoxide,14–16 alcohols,17–24 amines25,26 and sulfides,27,28 epoxidations of olefins,29 oxidative cleavage of carbon-carbon multiple bonds,30,31 etc. Therefore, it is still desirable to extend gold-catalyzed oxidation chemistry. 1,3,5-trisubstituted pyrazoles are one class of important compounds because heterocycles containing pyrazole moieties often exhibit valuable biological and medicinal activities, such as analgestic, anti-inflammatory, antipyretic, anti-arrhythmic, psychoanaleptic, antidiabetic and antibacterial ones.32–37 Generally, oxidative aromatization of 1,3,5-trisubstituted pyrazolines which could be easily prepared from the condensation of chalcones with arylhydrazines,38 is the most widely used protocol for synthesis of 1,3,5-trisubstituted pyrazole derivatives. To date, a variety of oxidants have been used for the purpose, e.g. zirconium (IV) nitrate,39 lead (IV) tetraacetate,40 silver (I) nitrate,41 bismuth (III) nitrate,42 manganese (IV) dioxide,43 potassium permanganate,44 mercury (II) oxide,45 iodobenzene diacetate,46 sodium nitrite and sodium nitrate in acetic acid,47 trichloroisocyanuric acid,48 4-(p-chloro)phenyl-1,3,4-triazole-3,5-dione,49 Pd/C,50 iodine pentoxide or iodic acid,51 activated carbon/oxygen system,52 and N-hydroxyphthalimide (NHPI)/cobalt acetate/oxygen sytem,53 etc. However, these processes have one or more limitations including high catalyst

An Effective Approach for the Silylation of Hydroxyl Compounds in Room Temperature Ionic Liquids

Abstract The room temperature ionic liquid (RTIL) 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMImPF6) is used as a “green” recyclable alternative to conventional solvents for the silylation of a series of hydroxyl compounds (alcohols and phenols) with t-butyldimethylchlorosilane (TBDMCS), which has some advantages such as simplicity of the synthetic procedure, the potential for recycling of the ionic liquid and the environmentally benign.

Novel atom-economic nitration of benzene with a nitrogen dioxide-oxygen system using cocatalyst of solid oxides and lanthanide(III) metal triflates

Abstract Benzene is nitrated by a novel atom‐economic nitration procedure with a NO2‐O2 system in the presence of a mixture of solid oxides and Ln(OTf)3. The only by‐product in this novel method is water. The efficiency of NO2 is much high than 50%, the theoretical efficiency of NO2 of the known methods. Among the solid oxides and Ln(OTf)3 studied, HZSM‐5 and Sm(OTf)3 were the most efficient catalysts in this process. Therewith, the yield of the benzene nitration reached 72.5%, calculated by NO2.

Highly enantioselective Michael reaction employing cycloheptanone and cyclooctanone as nucleophiles

An organocatalytic Michael reaction of cycloheptanone and cyclooctanone with nitrodienes and nitroolefins catalyzed by a hydroquinine-based primary amine catalyst has been accomplished. The corresponding Michael adducts were obtained in good yields (up to 88%) with good to excellent diastereoselectivities (up to >100 : 1) and enantioselectivities (up to >99% ee). The absolute configuration of the Michael product was assigned by TDDFT simulation of the ECD spectrum. And the Michael products can be readily converted into analogues of cycloalkano[b] fused pyrrolidines.