Trihaloisocyanuric acids as convenient reagents for regioselective halogenation of β-dicarbonyl compounds

The reaction of β-dicarbonyl compounds (β-ketoesters and β-diketones) with 0.34 mol equiv of trichloro- and tribromoisocyanuric acids produced regioselectively the corresponding α-monohalo β-dicarbonyl compound. On the other hand, utilization of 0.68 mol equiv of the trihaloisocyanuric acid produced the α,α-dihalo β-dicarbonyl compound.     

New chiral building blocks of β-peptoid analogs

The synthesis of chiral functionalized β-amino esters via the hydride reductive amination of chiral allenes was explored. These compounds can be regarded as β-peptoids building blocks bearing a chiral side chain at the nitrogen and at the same time retaining the β-amino acid side chain. β-Enamino esters were obtained from the nucleophilic addition of α-amino esters (l-Ala, d-Ala, l-Phe, l-Leu, l-Trp and d-Trp methyl esters) to 2,3-allenoates bearing a chiral auxiliary, which determines the stereochemistry outcome of the subsequent reduction reaction. It was also demonstrated that in the reduction of β-enamino esters derived from l-Pro and d-Pro methyl esters the chirality of the new chiral center is controlled by the α-amino ester moiety.     

等规聚丙烯β晶形态研究

本文用正交偏光显微镜和扫描电镜观察了加成核剂βIPP的晶体形态,发现偏光下βIPP为彩色树枝状,是由弧形晶片生长成的球晶,并提出了β晶是由一个中心向相反方向枝化生长的晶体模型。     

A simple nitration of electrophilic alkenes with tetranitromethane in the presence of triethylamine. Synthesis of functionalized β-nitroalkenes

A convenient method for the preparation of functionalized β-nitroalkenes based on the nitration of α,α-di- and α,α,β-trisubstituted unsaturated aldehydes, ketones and esters with tetranitromethane in the presence of triethylamine is described. Series of substituted β-nitroalcohols and β-nitroalkenes are obtained in good yields under mild conditions.     

New approach to exclusive formation of both enantiomers of β-amino acid derivatives

A highly selective two-step approach to chiral β-amino esters via the hydride reductive amination of chiral allenes is reported. β-Enamino esters were obtained from the nucleophilic addition of amines to 2,3-allenoates bearing a chiral auxiliary. The reduction of the (1R)-(−)-10-phenylsulfonylisobornyl β-enamino esters gave the corresponding β-amino esters with S configuration whereas the reduction of the (1S)-(+)-10-phenylsulfonylisobornyl β-enamino esters led to β-amino esters with R configuration. The rationalization of the observed selectivity was supported by semi-empirical molecular orbital calculations (PM3).     

An efficient one-step chemoselective reduction of alkyl ketones over aryl ketones in β-diketones using LiHMDS and lithium aluminium hydride

β-Hydroxy ketones were synthesized in one-pot from β-diketones by reducing alkyl ketones chemoselectively by keeping aryl ketone intact. Initially, β-diketones were enolized using LiHMDS and later alkyl ketone was chemoselectively reduced efficiently by lithium aluminium hydride. This method produces β- hydroxyl ketones from the corresponding β-diketones in high yield.     

An efficient one-pot synthesis of β-enamino ketones from endo glucal via hypervalent iodine

β-Enamino ketones were successfully synthesized by reaction of endo glycals with primary or secondary amines in the presence of hypervalent iodine reagent in one pot. After the oxidation and protonation taking place on hypervalent iodine agent in acidic condition, endo glucals were effectively converted into the uncyclic β-alkoxyvinyl ketones. Further substitution of β-alkoxyvinyl ketones with primary or secondary amines provided the corresponding β-enamino ketone derivatives in 57-67% yields.     

Synthesis of β-hydroxy selenides using benzeneselenol and oxiranes under supramolecular catalysis in the presence of β-cyclodextrin in water

A simple and efficient method for the synthesis of β-hydroxy selenides is reported at room temperature in impressive yields for the first time by the highly the regioselective ring-opening of oxiranes with benzeneselenol in water under supramolecular catalysis in the presence of β-cyclodextrin. This is a direct one-pot synthesis of β-hydroxy selenides under mild conditions using water as solvent and has many advantages over the existing methodologies. β-Cyclodextrin can also be recovered and reused.     

Non-isothermal crystallization, melting behavior and polymorphism of polypropylene in β-nucleated polypropylene/recycled poly(ethylene terephthalate) blends

β-Nucleated polypropylene (PP), non-compatibilized and compatibilized β-nucleated PP/recycled poly(ethylene terephthalate) (r-PET) blends were prepared on a twin-screw extruder. The compatibilizers were maleic anhydride grafted PP (PP-g-MA), glycidyl methacrylate grafted PP (PP-g-GMA), maleic anhydride grafted polyethylene-octene (POE-g-MA) and polyethylene-vinyl acetate (EVA-g-MA) elastomers. Effects of r-PET content, compatibilizer type and content, pre-melting temperature and time on the non-isothermal crystallization and melting behavior, and polymorphism of PP in the blends were investigated by differential scanning calorimeter (DSC). DSC results show that the crystallization temperature of PP crystallized predominantly in β-modification was higher than that of neat PP. In the non-compatibilized blend, PP matrix crystallized mainly in α-modification even if r-PET content was only 10 wt%. However, PP-g-MA compatibilization made PP matrix crystallize mainly in β-modification, but PP-g-GMA, POE-g-MA and EVA-g-MA did not improve the β-modification content distinctly. The α-crystal melting peak temperature of PP decreased with increasing pre-melting temperature, but r-PET content, compatibilizer type and content as well as pre-melting time had no obvious effect on the melting temperature of PP. The increase in PP-g-MA content, pre-melting temperature and time was benefit for the formation of β-modification. It is suggested that the β-nucleating agent is encapsulated or dissolved in polar r-PET in β-nucleated PP/r-PET blend, addition of PP-g-MA to the non-compatibilized blend resulted in transferring β-nucleating agent from r-PET phase into PP phase, the increase in PP-g-MA content, melting temperature and time was benefit for transferring β-nucleating agent from r-PET phase into PP phase. The non-isothermal crystallization kinetics of PP in the blends were evaluated by Mo’s method.     

Enantioselective synthesis of β-amino-diacids

An efficient route to orthogonally protected β-amino-diacids is described: chiral derivative 3 was shown to be a precursor of enantiopure substituted β-amino acids. The key step of the procedure is a diastereoselective reduction of β-enaminolactones 5 by NaBH₃CN in CH₂Cl₂. A study concerning the regio- and diastereoselectivity of alkylation of β-enaminolactone 3 is also presented.     

Highly enantioselective fluorination reactions of β-ketoesters and β-ketophosphonates catalyzed by chiral palladium complexes

Using chiral palladium enolates as key intermediates, efficient catalytic enantioselective fluorination reactions of active methine compounds have been developed. These reactions can be conducted in alcoholic solvents without any precaution to exclude water and moisture, and various β-ketoesters and β-ketophosphonates were fluorinated in a highly enantioselective manner (up to 98% ee).     

β-Cyclodextrin promoted aza-Michael addition of amines to conjugated alkenes in water

Highly efficient and environmentally benign aza-Michael additions of amines to α,β-unsaturated compounds catalyzed by β-cyclodextrin in water to produce the corresponding β-amino compounds in excellent yields under mild conditions are described. β-Cyclodextrin can be recovered and reused in subsequent reactions without loss of activity.     

Cycloaddition of cyclohexa-2,4-dienones with β-nitroacrylates: a short and efficient entry into bicyclo[2.2.2]octanes endowed with β-nitro-ester and β-amino ester functionality

Regio- and stereoselective cycloaddition of β-nitroacrylates with electron deficient cyclohexa-2,4-dienones leading to highly functionalised bicyclo[2.2.2]octanes having the β-nitroester group and their transformation to bicyclo[2.2.2]octanes having β-aminoester functionality is described.     

Regioselective ring-opening reactions of 1,2-epoxides with thiols and arylselenols directly promoted by [Bmim]BF4

Regioselective ring-opening reactions of 1,2-epoxides with ArSH and ArSeH promoted by ionic liquid [Bmim]BF₄ were investigated. A variety of β-hydroxy selenides and β-hydroxy sulfides were obtained in excellent yields (81-99%) with good regioselectivities using a mild, simple and environmentally benign procedure.     

Adsorption and Recovery of Ionic Surfactants by β-Cyclodextrin Polymer

The adsorption and recovery of ionic surfactants, such as dodecylbenzenesulfonic acid (DBS) and benzalkonium chloride (BKC), from an aqueous solution were studied using the β-cyclodextrin polymer (β-CDP). BKC always demonstrated a higher adsorption efficiency than DBS in batch tests, isotherms, and column tests. The adsorption characteristics of the surfactants seemed to be caused by inclusion into β-CD, and they were easily determined using the Langmuir adsorption isotherm. Furthermore, the surfactants adsorbed by β-CDP were easily released by shaking it with a mixture of water and methanol. Recovery efficiency was dependent on the mixture ratio of the solvent, and regenerated β-CDP was reusable as an adsorbent.     

Self-assembly of β-turn forming synthetic tripeptides into supramolecular β-sheets and amyloid-like fibrils in the solid state

We have described here the self-assembling properties of the synthetic tripeptides Boc-Ala(1)-Aib(2)-Val(3)-OMe 1, Boc-Ala(1)-Aib(2)-Ile(3)-OMe 2 and Boc-Ala(1)-Gly(2)-Val(3)-OMe 3 (Aib=α-amino isobutyric acid, β-Ala=β-alanine) which have distorted β-turn conformations in their respective crystals. These turn-forming tripeptides self-assemble to form supramolecular β-sheet structures through intermolecular hydrogen bonding and other noncovalent interactions. The scanning electron micrographs of these peptides revealed that these compounds form amyloid-like fibrils, the causative factor for many neurodegenerative diseases including Alzheimer's disease, Huntington's disease and Prion-related encephalopathies.     

A β-lactam-azasugar hybrid as a competitive potent galactosidase inhibitor

A β-lactam-azasugar hybrid (polyhydroxylated carbacephem) has been designed and synthesized as a potent glycosidase inhibitor.     

Thermal effect in β-selective glycosylation reactions using glycosyl iodides

The unique reactivity of glycosyl iodides and the fact that they react under neutral conditions makes them the donors of choice in our glycosylation strategies. Glycosyl iodides are generated in situ from either the anomeric acetate or the anomeric silylated derivative yielding the α-iodide. In the reported glycosylation reactions, protected glucosyl, galactosyl, and mannosyl iodides were reacted with trimethylene oxide as the acceptor, yielding the β-anomer as the major product. In the absence of neighboring group participation, β-selectivity is thought to arise from nucleophilic displacement of the α-iodide in an S_N2-like mechanism, while the α-product is the result of nucleophilic attack on the β-iodide. In this study, increased β-selectivity using an inverse thermal effect is demonstrated.     

成核剂含量对β晶相聚丙烯结晶与熔融行为的影响

用DSC研究了β成核剂含量对β聚丙烯在等温与非等温结晶条件下的结晶与熔融行为的影响,发现当成核剂含量为0.005％时,结晶焓△H_c、β晶的熔融焓△H_(mβ)及熔点T_(mβ)均为最大,而α晶的相对含量最小.广角X-衍射数据表明,成核剂含量高的试样的(301)衍射峰的相对强度下降,反映分子链排列的纵向有序性降低.根据聚丙烯分子在β成核剂上附生结晶的成核机理解释了上述结果.     

A recombinant ketoreductase tool-box. Assessing the substrate selectivity and stereoselectivity toward the reduction of β-ketoesters

The substrate selectivity and stereoselectivity of a series of ketoreductases were evaluated toward the reduction of two sets of β-ketoesters. Both the structural variety at β-position and the substituent at α-position greatly affected the activity and stereoselectivity of these ketoreductases. For the first set of β-ketoesters, at least one ketoreductase was found that catalyzed the formation of either (d) or (l) enantiomer of β-hydroxyesters from each substrate with high optical purity, with the only exception of ethyl (d)-3-hydroxy-3-phenylpropionate. For the second set of β-ketoesters with α-substituents, the situation is more complex. More commonly, a ketoreductase was found that formed one of the four diastereomers in optically pure form, with only a few cases in which enzymes could be found that formed two or more of the diastereomers in high optical purity. The continued development of new, more diverse ketoreductases will create the capability to produce a wider range of single diastereomers of 2-substituted-3-hydroxy acids and their derivatives.