Melt-Processable Semicrystalline Polyimides Based on 1,4-Bis(3,4-dicarboxyphenoxy)benzene Dianhydride (HQDPA): Synthesis, Crystallization, and Melting Behavior.

It is a great challenge to develop semicrystalline polyimides exhibited significant recrystallization ability and fast crystallization kinetics from the melt. A series of semicrystalline polyimides based on 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride (HQDPA) and different diamines, including 1,3-bis(4-aminophenoxy)benzene (TPER), 1,4-bis(4-aminophenoxy)benzene (TPEQ), 4,4'-oxydianiline (4,4'-ODA) and 4,4'-bis(4-aminophenoxy)biphenyl (BAPB), end capped with phthalic anhydride were synthesized. Crystallization and melting behaviors were investigated by differential scanning calorimetry (DSC). The polyimide derived from HQDPA/TPER (PI-1) exhibited a glass transition temperature (Tg) at 190 °C and double melting temperatures (Tms) at 331 °C and 350 °C, and the polyimide derived from HQDPA/TPEQ (PI-2) displayed a Tg at 214 °C and a Tm at 388 °C. PI-1 and PI-2 showed significant recrystallization ability from melt and high crystallization rate by isothermal crystallization kinetics study, while polyimides based on 4,4'-ODA and BAPB lost crystallizability once taken to the melt. These polyimides also exhibited excellent thermo-oxidative stability with 5% weight loss temperature higher than 500 °C and good mechanical properties with tensile moduli of 2.0⁻3.3 GPa, tensile strengths of 85⁻105 MPa and elongations at break of 5⁻18%. PI-1 also possessed outstanding melt flowability with less than 300 Pa·s around 370 °C by rheological measurements.

Synthesis of novel 1-[(2,6-dichloro-4-trifluoromethyl)phenyl]-3-aryl-1H-pyrazole-4-carbaldehydes.

A series of novel 1-[(2,6-dichloro-4-trifluoromethyl)phenyl]-3-aryl-¹H-pyrazole-4-carbaldehydes were synthesized using the Vilsmeier-Haack reagent. The structures of all the title compounds have been confirmed by elemental analysis, ¹H-NMR and ¹³C-NMR and in addition, the structure of intermediate 5b was investigated by X-ray crystallography.

Chemical composition of the green alga Codium Divaricatum Holmes.

A new sterol, 24-R-stigmasta-4,25-diene-3ß,6ß-diol (1), along with three known compounds (2-3), was isolated from the green alga Codium divaricatum Holmes, a traditional Chinese medicine, which is efficacious against cancer. All structures were determined by spectroscopic methods and comparison with related known compounds. Single-crystal X-ray crystallography allowed us to confirm the structure of 1. To our knowledge, the compound 1 is reported as the first from natural source, and compounds 2, 4 have not been isolated from green algae before.

In situ measurement of the enantiomeric excess of alcohols and amines under asymmetric reduction reaction by 1H NMR.

(1)H NMR, in situ, determines the enantiomeric excess of reduced chiral alcohols or amines without adding any auxiliary and workup. The percent ee data determined by this method agree well with those given by HPLC. This approach may be potentially applicable to many asymmetric reductions.

Pattern-based recognition for determination of enantiomeric excess, using chiral auxiliary induced chemical shift perturbation NMR.

A protocol for the determination of enantiomeric excess of chiral carboxylic acid, using the subtle frequency shifts (chemical shift perturbation) in NMR spectra induced by chiral auxiliary, is described. The spectra were analyzed with two pattern recognition protocols. Principal component analysis demonstrated good enantioselective separation of the analytes, and partial least-squares was used to analyze ee values of unknown samples.

Synthesis of novel 3,5-dichloro-2-arylpyridines by palladium acetate-catalyzed ligand-free Suzuki reactions in aqueous media.

A highly efficient palladium acetate-catalyzed ligand-free Suzuki reaction of 2,3,5-trichloropyridine with arylboronic acids in aqueous phase was developed. High yields of 3,5-dichloro-2-arylpyridines, a simple Pd source, absence of ligands, and environmentally benign as well as mild reaction conditions are important features of this method.

Chiral Brønsted acid-catalyzed asymmetric Friedel-Crafts alkylation of pyrroles with nitroolefins.

A highly efficient Friedel-Crafts reaction of pyrroles with nitroolefins by a chiral phosphoric acid was realized. With 5 mol % of catalyst, reactions conducted at rt afforded the 2-substituted or 2,5-disubstituted pyrroles in up to 94% ee for a wide range of substrates.

Asymmetric Friedel-Crafts reaction of 4,7-dihydroindoles with nitroolefins by chiral Brønsted acids under low catalyst loading.

Slowly does it! By adding the substrate by a syringe pump, a highly efficient Friedel-Crafts reaction of 4,7-dihydroindoles with nitroolefins was realized with 0.5 mol % of a chiral phosphoric acid. The Friedel-Crafts alkylation, together with a subsequent oxidation of the product, led to 2-substituted indoles in excellent enantiomeric excesses, which can be easily transformed to enantioenriched tetrahydro-gamma-carbolines.

Regioselective synthesis of 1-(2,6-dichloro-4-trifluoromethylphenyl)- 4-alkyl-1H-[1,2,3]-triazoles.

A new and efficient method for the synthesis of 1-(2,6-dichloro-4-trifluoromethylphenyl)-4-alkyl-1H-[1,2,3]-triazoles by the room temperature 1,3-dipolar cycloaddition of (2-azido-1,3-dichloro-5-trifluoromethyl)benzene with terminal alkynes in the presence of Cu (I) salt as catalyst is reported. All the reactions gave 1,4-disubstituted products with high regioselectivity, as no 1,5-disubstituted product was formed. The structures of all the title compounds have been confirmed by elemental analysis, 1H- and 13C-NMR and in addition, the structure of compound 5a was investigated by X-ray crystallography.

Synthesis and biological activity of some novel derivatives of 4-amino-3-(D-galactopentitol-1-yl)-5-mercapto-1,2,4-triazole.

To discover new 1,2,4-triazole derivatives which may possess significant biological activities, we synthesized a series of novel 6-aryl-3-(D-galactopentitol-1-yl)-7H-1,2,4-triazolo[3,4-b][1,3,4]thiadiazines and 4-(arylmethylidene)amino-5-(D-galactopentitol-1-yl)-3-mercapto-4H-1,2,4-triazoles from 4-amino-3-(D-galactopentitol-1-yl)-5-mercapto-1,2,4-triazole. All the title compounds were characterized by elemental analysis, IR, 1H- and 13C-NMR. Plant growth-regulating activity tests showed that these compounds have remarkable effects on the growth of radish and wheat.

Synthesis and biological evaluation of some novel Schiff's bases from 1,2,4-triazole.

We have synthesized a number of novel Schiff's bases from 4-amino-3-(D-glucoheptonic-hexitol-1-yl)-1H-1,2,4-triazole-5-thione. By attaching D-glucoheptonic-hexitol-1-yl residues to 1,2,4-triazole at the 3-position, the solubility of the title compounds has been improved greatly. All the products have been characterized by elemental analysis, IR, 1H-NMR, 13C-NMR and MS. The plant-growth regulating effects of the title compounds were examined. From the biological activity results, we found that most compounds showed weak to moderate activities.

Syntheses and biological activities of 6-aryl-3-(3-hydroxypropyl)-7H-1,2,4-triazolo[3,4-b][1,3,4]thiadiazines.

A series of 6-aryl-3-(3-hydroxypropyl)-7H-1,2,4-triazolo[3,4-b][1,3,4]-thiadiazines were synthesized by the reaction of 4-amino-3-(3-hydroxypropyl)-5-mercapto-1,2,4-triazole (1) with substituted omega-haloacetophenones. Their structures were confirmed by elemental analysis, IR, 1H-NMR, and 13C-NMR. Tests of plant growth regulating effects showed that the title compounds display remarkable inhibitory activities on the growth of radish and wheat.

1H and 13C NMR spectral characterization of some novel 7H-1,2,4-triazolo[3, 4-b] [1,3,4] thiadiazine derivatives.

Some novel 1, 2, 4-triazolo[3,4-b][1,3,4]thiadiazines derivatives were synthesized. The complete (1)H and (13)C NMR chemical shift assignments were analyzed on one- and two-dimensional NMR techniques, including DEPT, NOE-DIF, COSY, HMBC, and HSQC.

1H and 13C NMR study of 5-substituted-4- (arylidene)amino-2,4-dihydro-3H-1,2,4-triazole-3-thiones and 6-aryl-3-(D-gluco- pentitol-1-yl)-7H-1,2,4-triazolo[3,4-b] [1,3,4]thiadiazines.

Five 5-substituted-4-(arylidene)amino-2,4-dihydro-3H-1, 2,4-triazole-3-thiones (2a-2e) and seven 6-aryl-3-(D-gluco-pentitol-1-yl)-7H-1,2,4-triazolo[3,4-b][1,3,4]thiadiazines (3a-3g) were synthesized. The complete 1H and 13C NMR chemical shift assignments were analyzed on one- and two-dimensional NMR techniques, including DEPT, NOE-DIF, COSY, gHMBC, and gHSQC.

A highly enantioselective lewis basic organocatalyst for reduction of N-aryl imines with unprecedented substrate spectrum.

L-Pipecolinic acid derived formamides have been developed as highly efficient and enantioselective Lewis basic organocatalysts for the reduction of N-aryl imines with trichlorosilane. Catalyst 4b afforded high isolated yields (up to 98%) and enantioselectivities (up to 96%) under mild conditions with an unprecedented substrate spectrum.