Dan-Qian 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).

Fast, solvent-free and hydrogen-bonding-mediated asymmetric Michael addition in a ball mill

The chiral squaramide derivatives as hydrogen bonding catalyst for the Michael addition reactions of 1,3-dicarbonyl compounds to nitroolefins under solvent-free conditions was developed using a planetary ball mill. High yields, high enantioselectivities and shorter reaction times were achieved with low catalyst loading.

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.

One‐Pot Organocatalytic Asymmetric Synthesis of 3‐Nitro‐1,2‐dihydroquinolines by a Dual‐Activation Protocol

Generally, amine-catalyzed enantioselective transformations rely on chiral enamine or unsaturated iminium intermediates. Herein, we report a protocol involving dual activation by an aromatic iminium and hydrogen-bonding. An enantioselective aza-Michael-Henry domino reaction of 2-aminobenzaldehydes with nitroolefins has been developed through this protocol using primary amine thiourea catalysts to provide a variety of 3-nitro-1,2-dihydroquinolines in moderate yields and with up to 90% ee. The mechanism for the catalytic enantioselective reaction was confirmed by ESI mass spectrometric detection of the reaction intermediates. The products formed are substructures found in skeletons of important biological and pharmaceutical molecules.

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.

Fast, solvent-free and highly enantioselective fluorination of β-keto esters catalyzed by chiral copper complexes in a ball mill

A fast and highly enantioselective fluorination of β-keto esters catalyzed by diphenylamine linked bis(oxazoline)-Cu(OTf)2 complexes under solvent-free conditions has been developed using a planetary ball mill. High yields, high enantioselectivities and shorter reaction times were achieved with low catalyst loading.

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.

Enantioselective synthesis of functionalized 3,4-disubstituted dihydro-2(1H)-quinolinones via Michael–hemiaminalization/oxidation reaction

A novel method is developed for the enantioselective synthesis of highly functionalized 3,4-disubstituted dihydro-2(1H)-quinolinones bearing two trans contiguous stereogenic centers with excellent diastereoselectivities (up to >99 : 1 dr) and high to excellent enantioselectivities (up to >99% ee). The process combines an enantioselective organocatalytic Michael–hemiaminalization reaction and a highly efficient oxidation reaction sequence with good yields and stereoselectivity.

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.