Two solvent-induced porous hydrogen-bonded organic frameworks: solvent effects on structures and functionalities.

Two solvent-induced porous hydrogen-bonded organic frameworks have been obtained, and their synthesis, crystal structures, gas sorption behaviours and fluorescence sensing applications have been systematically investigated to elucidate the solvent effects on the structures and functionalities of HOFs.

Asymmetric Aldol Reaction of 3-Acetyl-2H-chromen-2-ones and Isatins Catalyzed by a Bifunctional Quinidine Urea Catalyst.

The asymmetric aldol reaction of 3-acetyl-2H-chromen-2-ones and isatins has been realized by using a bifunctional quinidine-derived urea as the catalyst. The corresponding 3-hydroxyoxindole derivatives containing a 2H-chromen-2-one moiety were obtained in good yields and high enantioselectivities. When (Z)-ethyl 2-benzylideneacetoacetate was used as the substrate, a mixture of two diastereomers (both Z and E) was obtained due to the isomerization of the double bond under the reaction conditions.

A homochiral microporous hydrogen-bonded organic framework for highly enantioselective separation of secondary alcohols.

A homochiral microporous hydrogen-bonded organic framework (HOF-2) based on a BINOL derivative has been synthesized and structurally characterized to be a uninodal 6-connected {3(3)5(5)6(6)7} network. This new HOF exhibits not only a permanent porosity with the BET of 237.6 m(2) g(-1) but also, more importantly, a highly enantioselective separation of chiral secondary alcohols with ee value up to 92% for 1-phenylethanol.

Water residing in small ultrastructural spaces plays a critical role in the mechanical behavior of bone.

Water may affect the mechanical behavior of bone by interacting with the mineral and organic phases through two major pathways: i.e. hydrogen bonding and polar interactions. In this study, dehydrated bone was soaked in several solvents (i.e. water, heavy water (D2O), ethylene glycol (EG), dimethylformamide (DMF), and carbon tetrachloride(CCl4)) that are chemically harmless to bone and different in polarity, hydrogen bonding capability and molecular size. The objective was to examine how replacing the original matrix water with the solvents would affect the mechanical behavior of bone. The mechanical properties of bone specimens soaked in these solvents were measured in tension in a progressive loading scheme. In addition, bone specimens without any treatments were tested as the baseline control whereas the dehydrated bone specimens served as the negative control. The experimental results indicated that 22.3±5.17vol% of original matrix water in bone could be replaced by CCl4, 71.8±3.77vol% by DMF, 85.5±5.15vol% by EG, and nearly 100% by D2O and H2O, respectively. CCl4 soaked specimens showed similar mechanical properties with the dehydrated ones. Despite of great differences in replacing water, only slight differences were observed in the mechanical behavior of EG and DMF soaked specimens compared with dehydrated bone samples. In contrast, D2O preserved the mechanical properties of bone comparable to water. The results of this study suggest that a limited portion of water (<15vol% of the original matrix water) plays a pivotal role in the mechanical behavior of bone and it most likely resides in small matrix spaces, into which the solvent molecules larger than 4.0Å cannot infiltrate.

Organocatalyzed asymmetric Michael reaction of ß-aryl-α-ketophosphonates and nitroalkenes.

The first enantioselective Michael reaction of ß-aryl-α-ketophosphonates and nitroalkenes has been brealized by using a new bifunctional Takemoto-type thiourea catalyst. The primary Michael adducts obtained were converted in situ to the corresponding amides through the aminolysis. High yields, excellent diastereoselectivities (>95:5 dr), and good enantioselectivities (up to 81% ee) have been achieved for the corresponding α ,ß-disubstituted γ-nitroamides. This reaction againdemon strated that α-ketophosphonates are interesting pronucleophiles that can be used as amide surrogates in organocatalyzed reactions.

List-Barbas-Mannich reaction catalyzed by modularly designed organocatalysts.

The List-Barbas-Mannich reaction of ethyl (p-methoxyphenylimino)acetate (p-methoxyphenyl = PMP) with unmodified aldehydes or ketones catalyzed by modularly designed organocatalysts (MDOs) that are self-assembled from proline and cinchona alkaloid thioureas (such as a quinidine-derived thiourea) produces the corresponding γ-oxo-α-amino acid derivatives in high yields and excellent stereoselectivities. No solvent is necessary for this reaction. Aldehydes are especially good substrates for this reaction: The reaction takes only a few minutes to yield the corresponding List-Barbas-Mannich products in excellent dr (up to >99:1) and ee values (up to >99% ee).

Enantioselective ring-opening of meso-epoxides by aromatic amines catalyzed by a homochiral metal-organic framework.

The enantioselective ring-opening of meso-epoxides by aromatic amines was achieved by using a new chiral metal-organic framework . The corresponding α-hydroxyamines were obtained with good yields and ee values (up to 89% ee).

Highly stereoselective synthesis of 2,6-cis-substituted tetrahydropyrans using a one-pot sequential catalysis.

A catalytic highly diastereo- and enantioselective synthesis of 2,6-cis-substituted tetrahydropyrans was realized using a one-pot sequential catalysis involving Henry and oxa-Michael reactions. The nitroaldol products obtained in a highly enantioselective copper(II)-catalyzed Henry reaction between nitromethane and 7-oxo-hept-5-enals were subsequently treated with a catalytic amount of camphorsulfonic acid (CSA) to give the desired tetrahydropyran derivatives in excellent yields, diastereoselectivities (dr >99:1), and enantioselectivities (ee = 98-99%). The reaction can also be used for the high stereoselective synthesis of a cis-2,6-disubstituted morpholine.

Highly stereoselective synthesis of trisubstituted cyclohexanols using a guanidine-catalyzed tandem Henry-Michael reaction.

A highly diastereoselective (dr >99:1) and enantioselective (ee value up to 98%) synthesis of trisubstituted cyclohexanols was achieved by using a tandem Henry--Michael reaction between nitromethane and 7-oxo-hept-5-enals catalyzed by the Misaki-Sugimura guanidine.

Highly enantioselective three-component direct Mannich reactions of unfunctionalized ketones catalyzed by bifunctional organocatalysts.

A highly stereoselective three-component direct Mannich reaction between aromatic aldehydes, p-toluenesulfonamide, and unfunctionalized ketones was achieved through an enolate mechanism for the first time with a bifunctional quinidine thiourea catalyst. The corresponding N-tosylated ß-aminoketones were obtained in high yields and excellent diastereo- and enantioselectivities (up to >99:1 dr and >99% ee).

One-pot sequential organocatalysis: highly stereoselective synthesis of trisubstituted cyclohexanols.

A highly diastereoselective (d.r. >99:1) and enantioselective (ee value up to 96%) synthesis of trisubstituted cyclohexanols was achieved by using a one-pot sequential organocatalysis that involved a quinidine thiourea-catalyzed tandem Henry-Michael reaction between nitromethane and 7-oxo-hept-5-en-1-als followed by a tetramethyl guanidine (TMG)-catalyzed tandem retro-Henry-Henry reaction on the reaction products of the tandem Henry-Michael reaction. Through a mechanistic study, it has also been demonstrated that similar results may also be achieved with this one-pot sequential organocatalysis by using the racemic Henry product as the substrate.

Highly diastereo- and enantioselective organocatalytic one-pot sequential 1,4-addition/dearomative-fluorination transformation.

Fluorination: A wide range of nitroolefins and pyrazol-5-ones undergo a sequential 1,4-addition/dearomative-fluorination transformation when treated with a catalytic amount of a tertiary-amine-thiourea compound and the terminal electrophile, N-fluorobenzenesulfonimide, to give fluorinated products in 72-95% yield with up to 99:1 d.r. and 98% ee. Notably, these products contain adjacent tertiary and α-fluoro quaternary stereocenters (see scheme).

Multi-component synthesis of 2-amino-6-(alkyllthio)pyridine-3,5-dicarbonitriles using Zn(II) and Cd(II) metal-organic frameworks (MOFs) under solvent-free conditions.

Multi-component synthesis 2-amino-3,5-dicarbonitrile-6-thio-pyridines has been developed by using the reaction of aldehydes, malononitrile, and thiophenols in the presence of a Zn (II) or a Cd(II) metal-organic framework (MOF) as the heterogeneous catalyst. This protocol tolerates different functional groups on the substrates and does not require the use of any organic solvent. Moreover, the Zn(II) and Cd (II) MOF catalysts can be recovered and reused for a number of runs without loss of activity.

Acetylphosphonate as a surrogate of acetate or acetamide in organocatalyzed enantioselective aldol reactions.

Highly enantioselective aldol reactions of acetylphosphonates and activated carbonyl compounds was realized with cinchona alkaloid derived catalysts, in which the acetylphosphonate was directly used as an enolate precursor for the first time. The aldol product obtained was converted in situ to its corresponding ester or amide through methanolysis or aminolysis. The overall process may be viewed as formal highly enantioselective acetate or acetamide aldol reactions, which are very difficult to achieve directly with organocatalytic methods.