Catalytic, asymmetric synthesis of α-acetoxy amides

Non-racemic cyanohydrin acetates are readily available from aldehydes and potassium cyanide/acetic anhydride by use of bimetallic titanium (salen) catalyst 1. Treatment of the cyanohydrin acetates with a platinum(II) phosphinito catalyst 3 under neutral conditions results in chemoselective hydrolysis to the corresponding α-acetoxy amides in a racemization free process.     

Synthesis of alpha-amino acids via asymmetric phase transfer-catalyzed alkylation of achiral nickel(II) complexes of glycine-derived Schiff bases

Achiral, diamagnetic Ni(II) complexes 1 and 3 have been synthesized from Ni(II) salts and the Schiff bases, generated from glycine and PBP (7) and PBA (11), respectively, in MeONa/MeOH solutions. The requisite carbonyl-derivatizing agents pyridine-2-carboxylic acid(2-benzoyl-phenyl)-amide 7 (PBP) and pyridine-2-carboxylic acid(2-formyl-phenyl)-amide 11 (PBA) were readily prepared from picolinic acid and o-aminobenzophenone or picolinic acid and methyl o-anthranilate, respectively. The structure of 1 was established by X-ray crystallography. Complexes 1 and 3 were found to undergo C-alkylation with alkyl halides under PTC conditions in the presence of beta-naphthol or benzyltriethylammonium bromide as catalysts to give mono- and bis-alkylated products, respectively. Decomposition of the complexes with aqueous HCl under mild conditions gave the required amino acids, and PBP and PBA were recovered. Alkylation of 1 with highly reactive alkyl halides, carried out under the PTC conditions in the presence of 10% mol of (S)- or (R)-2-hydroxy-2'-amino-1,1'-binaphthyl 31a (NOBIN) and/or its N-acyl derivatives and by (S)- or (R)-2-hydroxy-8'-amino-1,1'-binaphthyl 32a (iso-NOBIN) and its N-acyl derivatives, respectively, gave rise to alpha-amino acids with high enantioselectivities (90-98.5% ee) in good-to-excellent chemical yields at room temperature within several minutes. An unusually large positive nonlinear effect was observed in these reactions. The Michael addition of acrylic derivatives 37 to 1 was conducted under similar conditions with up to 96% ee. The (1)H NMR and IR spectra of a mixture of the sodium salt of NOBIN and 1 indicated formation of a complex between the two components. Implications of the association and self-association of NOBIN for the observed sense of asymmetric induction and nonlinear effects are discussed.     

Ene-diamine versus imine-amine isomeric preferences

Cyanide-catalyzed aldimine coupling was employed to synthesize compounds with 1,2-ene-diamine and alpha-imine-amine structural motifs: 1,2,N,N'-tetraphenyletheylene-1,2-diamine (13) and (+/-)-2,3-di-(2-hydroxyphenyl)-1,2-dihydroquinoxaline (17), respectively. Single-crystal X-ray diffraction provided solid-state structures and density functional theory calculations were used to probe isomeric preferences within this and the related hydroxy-ketone/ene-diol system. The ene-diamine and imine-amine core structures were calculated (B3LYP/6-311++G(d,p)) to be essentially identical in energy (DeltaG = 0.2 kcal/mol in favor of the imine-amine, within the error of the calculation). However, additional effects-such as pi conjugation-in 13 render an ene-diamine structure that is slightly more stable than the imine-amine tautomer (14) (DeltaG = 0.2-0.7 kcal/mol, within the error of the calculation). In contrast, the intramolecular hydrogen bonding present in 17 significantly favors the imine-amine isomer over the ene-diamine tautomer (18) (DeltaG = 7.2-8.9 kcal/mol). For both 13 and 17, the optimized calculated structures (B3LYP/6-31+G(d')) are identical to those observed by single-crystal X-ray diffraction.     

Kinetics of silicate exchange in alkaline aluminosilicate solutions

In strongly alkaline aqueous KOH solutions containing SiIV in large excess over AlIII, the kinetics of exchange of monomeric silicate with small acyclic aluminosilicate solute species is much more rapid than with either cyclic aluminosilicates or any all-silicate anions. Selective inversion recovery 29Si NMR studies of homogeneous solutions of stoichiometric composition 3.0 mol kg-1 of SiO2, 0.1 mol kg-1 of Al2O3, and 8.0 mol kg-1 of K2O in 60-75% D2O gave rate constants of 2.0 +/- 0.2 kg mol-1 s-1 and 17 +/- 4 s-1 for the forward and reverse reactions of monomeric silicate with (HO)3AlOSiOn(OH)(3-n)(n+1)- (n = 2 or 3) at 0 degree C. These rate constants are more than 10(4)-fold faster than those extrapolated from 60 to 90 degrees C for comparable reactions of silicate anions. The greater lability of acyclic aluminate centers relative to silicate is ascribed partly to the availability of HO- groups for condensation reactions on Al and mainly to the ease of expansion of the coordination number of AlIII beyond 4. The latter attribute is diminished when AlIII is constrained to be tetrahedral in cyclic structures. With respect to the mechanism of formation of zeolites from alkaline aqueous media, it is suggested that small, labile AlOSi units add rapidly to growing zeolitic structures "on demand", whereas the more kinetically inert cage or ring structures cannot. This would explain why a silicate or aluminosilicate structure that is dominant among solute species at equilibrium in the presence of a particular cation may bear little or no geometric relation to the zeolitic framework promoted kinetically by that same cation.     

Ene-yne-ene and ene-yne-yne metathesis of norbornene derivatives

Norbornene derivatives 4 and 5 containing sidechains bearing an internal alkyne and either a terminal alkene or a terminal alkyne were found to undergo a cascade of metathesis reactions when treated with ruthenium based metathesis catalysts to form highly functionalised pentacyclic products. The reactions illustrate an interesting difference in reactivity between Grubbs’ catalyst and the second generation catalyst, with the former being more reactive for the early steps of the cascade.     

Catalytic asymmetric synthesis of O-acetyl cyanohydrins from KCN,Ac2O and aldehydes

A (salen)titanium catalyst has been found to induce the asymmetric addition of potassium cyanide and acetic anhydride to aldehydes, giving enantiomerically enriched cyanohydrin esters with up to 92% enantiomeric excess using just 1 mol% of the catalyst. This is the first report of the asymmetric synthesis of cyanohydrin derivatives using a cyanide source which is non-volatile and inexpensive.     

Importance of Micropore–Mesopore Interfaces in Carbon Dioxide Capture by Carbon‐Based Materials

Mesoporous carbonaceous materials (Starbons®) derived from low‐value/waste bio‐resources separate CO₂ from CO₂/N₂ mixtures. Compared to Norit activated charcoal (AC), Starbons® have much lower microporosities (8–32 % versus 73 %) yet adsorb up to 65 % more CO₂. The presence of interconnected micropores and mesopores is responsible for the enhanced CO₂ adsorption. The Starbons® also showed three–four times higher selectivity for CO₂ adsorption rather than N₂ adsorption compared to AC.     

Synthesis of a hybrid MIL-101(Cr)/ZTC composite for hydrogen storage applications

Metal–organic frameworks (MOFs) hybrid composites have recently attracted considerable attention in hydrogen storage applications. In this study a hybrid composite of zeolite templated carbon (ZTC) and Cr-based MOF (MIL-101) was synthesised by adding the templated carbon in situ during the synthesis of MIL-101(Cr). The obtained sample was fully characterized and hydrogen adsorption measurements performed at 77 K up to 1 bar. The results showed that the surface areas and the hydrogen uptake capacities of individual MIL-101 (2552 m² g^?1, 1.91 wt%) and zeolite templated carbon (2577 m² g^?1, 2.39 wt%) could be enhanced when a hybrid MIL-101(Cr)/ZTC composite (2957 m² g^?1, 2.55 wt%) was synthesized. The procedure presents a simple way for enhancement of hydrogen uptake capacity of the individual Cr-MOF and templated carbon samples.     

Synthesis and Herbicidal Activity of Novel Sulfonylurea Derivatives

Sulfonylurea herbicides have been applied worldwide in agriculture. Some sulfonylurea residues might exist in soil longer than that people expected. However, flupyrsulfuron-methyl-sodium which was firstly reported as a new 5-substituted sulfonylurea herbicide has less than one month residual life. Therefore, 5-substituted benzenesulfonylureas are potential molecules to regulate its residual situation. In order to develop new sulfonylurea derivatives, the substituent on the critical 5-posotion of the benzene...     

快速溶解法在测定硅铁及其合金元素中的应用

建立快速溶解硅铁及其合金的试验方法,并利用电感耦合等离子体发射光谱仪分析检测硅铁及其合金中微量元素及痕量元素,证明了快速溶解法的可行性.结果显示,方法的精密度及检测仪器重复性测量不确定度的结果均符合国家标准规定的允许偏差范围,说明快速溶解法具有一定推广价值和应用前景.