Stereoselective Synthesis of (Z)- and (E)-Allylic Silanes by Copper-Mediated Substitution Reactions of Allylic Carbamates with Grignard Reagents

Both (Z)- and (E)-allylic silanes were prepared with high stereoselectivity by the copper-mediated substitution of allylic carbamates by organometallic reagents. The reaction of alkylmagnesium reagents with (E)-allylic carbamates provides (Z)-allylic silanes, whereas both alkylmagnesium and alkyllithium reagents react with (Z)-allylic carbamates to afford (E)-allylic silanes. Because Grignard reagents are often more facile to prepare than alkyllithium species, these reagents are the optimal nucleophiles for the synthesis of both (Z)- and (E)-allylic silanes. This method also allows readily available nonracemic allylic carbamates to be converted to chiral, nonracemic (Z)- and (E)-allylic silanes with high stereoselectivity.     

长链烷基(2-羟乙基)二甲基氯化铵用作分析增敏试剂

合成了3种含季氮原子及羟基的同系列分析增敏试剂十六烷基(2-羟乙基)二甲基氯化铵(HEMAC)、十四烷基(2-羟乙基)二甲基氯化铵(TEMAC)和十二烷基(2-羟乙基)二甲基氯化铵(DEMAC),测试其基本物性,并用作测定微量钪、铁(Ⅲ)、锗的增敏试剂,获得了与阳离子表面活性剂及醇类有机溶剂联用时相仿的增敏效果。     

Structure and Reactivity of N-Heterocyclic Alkynyl Hypervalent Iodine Reagents

Ethynylbenziodoxol(on)e (EBX) cyclic hypervalent iodine reagents have become popular reagents for the alkynylation of radicals and nucleophiles, but only offer limited possibilities for further structure and reactivity fine-tuning. Herein, the synthesis of new N-heterocyclic hypervalent iodine reagents with increased structural flexibility based on amide, amidine and sulfoximine scaffolds is reported. Solid-state structures of the reagents are reported and the analysis of the I−C_alkyne bond lengths allowed assessing the trans-effect of the different substituents. Molecular electrostatic potential (MEP) maps of the reagents, derived from DFT computations, revealed less pronounced σ-hole regions for sulfonamide-based compounds. Most reagents reacted well in the alkynylation of β-ketoesters. The alkynylation of thiols afforded more variable yields, with compounds with a stronger σ-hole reacting better. In metal-mediated transformations, the N-heterocyclic hypervalent iodine reagents gave inferior results when compared to the O-based EBX reagents.     

Molecular Lamps and Molecular Golf Balls

The concave shielding of the active site of enzymes has been transferred to standard reagents of organic chemistry and concave reagents have been synthesized which possess a lamp-like geometry (concave 1,10-phenanthrolines 1–2, concave pyridines 3). The special concave geometry of these reagents is responsible for their selectivity in metal ion catalyzed (Pd-catalyzed allylations, Cu(I)-catalyzed cyclopropanations) and base catalyzed (acylation of alcohols by ketenes) reactions. For an easier recovery, these reagents have been attached to Merrifield polymers and to dendrimers. Higher generations of dendrimers loaded with concave reagents will possess a golf ball geometry.     

Uncatalysed coupling of an activated aryl chloride with aryllithium and aryl Grignard reagents

Substitution of the chloro group in 2-(2-chlorophenyl)-4,4-dimethyl-2-oxazoline to afford biaryls occurs upon reaction with either aryllithium reagents or aryl Grignard reagents. The reactions with Grignard reagents occur under similar conditions to a previously reported manganese-catalysed procedure. The reactions with lithium reagents, whilst not always affording greater yields of product than the Grignard reagents, involve much shorter reaction times and afford yields, which are comparable with those obtained from the corresponding fluoro derivative.     

Stéréochimie des réactions de substitution des alcoxygermanes par les organolithiens et par les réactifs de Grignard

The reactions of organolithium reagents and Grignard reagents with optically active alkoxygermanes R₃GeOR′ have been studied [R₃GeOR′ = ()-i-PrPhNpGeOCH₃, ()-i-PrPhNPGeOMen and ()-MePhNpGeOMen]. Saturated reagents (e.g. butyllithium) give retention of configuration at germanium whilst unsaturated reagents (e.g. allyl- or benzyllithium) lead to inversion.     

Reagents with a Crystalline Coat

Tetrakis(dimethoxyphenyl)adamantane (TDA) readily forms crystalline inclusion complexes with reactive, toxic, or malodorous reagents, such as benzoyl chloride, acetyl chloride, cyclohexyl isocyanide, phosphorus trichloride, and trimethylsilyl chloride. The crystals are stable and largely free of the problematic properties of the free reagents. When exposed to solvents such as DMSO or MeOH, the reagents react, and a large portion of the TDA precipitates. The TDA‐coated reagents may lead to a safer way of storing, handling, and delivering reagents, and ultimately to synthetic protocols that do not require fume hoods.     

Asymmetric allylic alkylation of acyclic allylic ethers with organolithium reagents

A highly efficient, regio- and enantioselective Cu(I) /phosphoramidite-catalyzed asymmetric allylic alkylation of allyl ethers with organolithium reagents is reported. The use of organolithium reagents is essential for this catalytic C?C bond formation due to their compatibility with different Lewis acids. The versatility of allylic ethers under the copper-catalyzed reaction conditions with organolithium reagents is demonstrated in the shortest synthesis of (S)-Arundic acid.     

量子化学在分析试剂反应性能中的应用

本文对量子化学方法应用于分析化学的有机显色反应能作一综述，重点从量子化学在生色理论，在试剂络合性能研究中，在试剂质子化及其酸碱平衡和存在形成研究中以及在取代基效应的中的应用四个方面进行了论述，重点介绍我国在这一方面的工作。认为用量子化学方法预测试剂和络合物的某些性质成为可能。参考文献６０篇。     

Indirect enantioseparation of alpha-amino acids by reversed-phase liquid chromatography using new chiral derivatizing reagents synthesized from s-triazine chloride

Ten chiral dichloro- and monochloro-s-triazines were prepared by the nucleophilic displacement of chlorine atom(s) in s-triazine chloride and its 6-methoxy derivative with different amino acid amides. Dichloro-s-triazines (DCTs) were used as CDRs for derivatization of alpha-amino acids under basic conditions at room temperature (30 degrees C) while derivatization with monochloro-s-triazine (MCT) reagents was carried out at 80 degrees C. The resultant diastereomers were separated on a reversed-phase C(18) column using mixtures of acetonitrile and aqueous-trifluoroacetic acid (TFA). The separation results for the two were compared. One DCT reagent was optimized for derivatization kinetics with respect to the effects of pH, reagent excess, temperature and reaction time on derivatization yield. In most of the cases, DCT reagents provided better separation of diastereomers in comparison to MCT reagents. One DCT reagent was also validated for limit of detection, linearity, recovery and robustness. Effects of structural modifications in reagents on chromatographic properties were investigated. Separation mechanism of diastereomers was proposed in light of both MCT and DCT reagents.     

Palladium-catalyzed coupling of thiol esters with aryl and primary and secondary alkyl organoindium reagents

Thiol esters and organoindium reagents undergo palladium-catalyzed cross-coupling under mild conditions to give ketones in moderate to excellent yields. Aryl and primary/secondary alkyl organoindium reagents can be used as coupling partners. This method has two advantages over the cross-coupling of thiol esters with boron and tin reagents: (1) no added copper reagent is required to mediate the reaction and (2) for the case of alkyl transfer, no added base is required to activate organoindium reagents for cross-coupling as is required for the coupling of alkyl boron reagents with thiol esters.     

Preparation of allyltin reagents grafted on solid support: clean and easily recyclable reagents for allylation of aldehydes

The preparation of polymer-supported allyltin reagents was shown to be possible for both unfunctionalized and functionalized allyl units. These reagents were treated with aldehydes in the presence of cerium(III) or indium(III) salts to afford high yields of homoallylic alcohols, practically uncontaminated with organotin residues (less than 5 ppm). Some mechanism aspects are briefly discussed and the potential for regeneration and reuse of these supported reagents is pointed out.     

Oxidation Catalysis by an Aerobically Generated Dess–Martin Periodinane Analogue

Hypervalent iodine(V) reagents, such as Dess–Martin periodinane (DMP) and 2‐iodoxybenzoic acid (IBX), are broadly useful oxidants in chemical synthesis. Development of strategies to generate these reagents from dioxygen (O₂) would immediately enable use of O₂ as a terminal oxidant in a broad array of substrate oxidation reactions. Recently we disclosed the aerobic synthesis of I(III) reagents by intercepting reactive oxidants generated during aldehyde autoxidation. In this work, aerobic oxidation of iodobenzenes is coupled with disproportionation of the initially generated I(III) compounds to generate I(V) reagents. The aerobically generated I(V) reagents exhibit substrate oxidation chemistry analogous to that of DMP. The developed aerobic generation of I(V) has enabled the first application of I(V) intermediates in aerobic oxidation catalysis.     

Reactions of substituted (1,3-butadiene-1,4-diyl)magnesium, 1,4-bis(bromomagnesio)butadienes and 1,4-dilithiobutadienes with ketones, aldehydes and PhNO to yield cyclopentadiene derivatives and N-Ph pyrroles by cyclodialkenylation

1,4-Dilithiobutadiene derivatives 1, 1,4-bis(bromomagnesio)butadiene derivatives 2 and metallacyclic (1,3-butadiene-1,4-diyl)magnesium reagents 3 were prepared and their reactions with ketones, aldehydes, and PhNO were investigated. Multiply substituted cyclopentadienes and N-Ph pyrroles were formed by unprecedented reaction conditions. The carbonyl group of aldehydes and ketones was deoxygenated during the reaction and behaved formally as a one-carbon unit; the N==O moiety of PhNO was cleaved to afford N-Ph pyrrole derivatives. Furthermore, different reactivities among these three types of reagents 1, 2 and 3 were revealed. The 1,4-dilithium reagents 1 readily reacted with both aldehydes and ketones; the 1,4-dimagnesium reagents 2 reacted with aldehydes, but not ketones; the metallacyclopentadiene reagents of magnesium 3 showed higher reactivity and did react with ketones.     

Synthesis and evaluation of fluorogenic reagents for simultaneous detection of peptides and proteins by HPLC in two different samples

To find the pairs of fluorogenic reagents having similar retention times in HPLC but with different fluorescent characteristics, six fluorogenic reagents bearing benzoxadiazole or benzoselenadiazole skeletons were synthesized. The resultant derivatives obtained from the reaction of peptides and proteins with reagents which have a benzoselenadiazole skeleton showed different fluorescence characteristics from those with a benzoxadiazole skeleton. Since each corresponding derivatives of trypsin inhibitor and BSA with DAABD-Cl and 7-fluoro-N-[2-(diethylamino)ethyl]-2,1,3-benzoselenadiazole-4-sulfonamide (DEAEABSeD-F) have similar retention times, the pair of reagents was adopted for the sensitive simultaneous detection of proteins in two different samples. When the soluble fraction of mouse hippocampus was divided into the two samples (A and B), each was reacted with DEAEABSeD-F for A and DAABD-Cl for B, respectively. The two reaction solutions were combined and subjected to HPLC analysis with two fluorescent detectors in series (excitation and emission at different wavelengths for A and B, respectively). The resultant two chromatograms had quite similar patterns for each other. The new pair of fluorogenic reagents (DAABD-Cl and DEAEABSeD-F) would be applicable to proteomics studies using the previously reported FD-LC-MS/MS method.     

三氮烯试剂的结构与性能关系的研究

为建立三氮烯试剂结构与性能的关系, 我们研究了在非离子型表面活性剂TritonX-100存在下, 上述试剂亚氨基氢的酸性离解常数及镉(II)与上述试剂的显色反应。研究结果表明: (1)三氮烯试剂亚氨基氢的酸性离解常数遵循Hammett方程式, 其反应常数ρ=2.23; (2)试剂的亚氨基氢的酸性离解常数(pKa)与试剂和镉(II)显色反应的最佳酸度(pH最佳)之间的经验关系式为pH最佳=pKa-(1.70±0.20)。     

Titrimetric determination of thiols: Tetrathionate, iron(III), cystine and hexacyanoferrate(III) as thiol reagents

Four analytical reagents, tetrathionate, iron(III), cystine and hexacyanoferrate(III) have been tested with respect to their specificity for oxidation of thiols to disulphides. Of a number of thiols studied, most have a strong tendency to oxidize beyond the disulphide stage with several of the commonly employed reagents. Tetrathionate, cystine and hexacyanoferrate(III) function in phosphate buffer of pH 7, but iron(III) does not require rigid control of pH, although the solution should be only feebly acidic. The reagents were used in excess and the thiosulphate or cysteine formed in the reaction of thiols with tetrathionate or cystine respectively was determined. The residual iron(III) was measured by adding ascorbic acid or mercaptoacetic acid and titrating with 2,6-dichlorophenolindophenol or iodine monochloride respectively; surplus hexacyanoferrate(III) was back-titrated with ascorbic acid. All four reagents react selectively with thiols even in the presence of several possible interfering substances and afford results that are accurate and precise.     

Synthesis of 5S-(1-Oxoalkyl and Aryl)-2-pyrrolidinone Derivatives1

N-Benzyl pyroglutamate esters react with aryllithium reagents and methyllithium to give moderate to good yields of 5-(1-oxoaryl) or 5-(1-oxoalkyl)-2-pyrrolidinone derivatives. The reaction proceeds without racemization, but is accompanied by formation of 5-(1-hydroxy-1-alkyl)-2-pyrrolidinone derivatives. This reaction gives very poor yields of ketone products with most other alkyl organolithium reagents such as n-butyllithium. Grignard reagents react to give primarily the alcohol.     

Palladium(0)-catalyzed cis-selective alkylative and arylative cyclization of alkynyl enones with organoboron reagents

A palladium(0)-tricyclohexylphosphine catalyzes cis-selective alkylative and arylative cyclization of alkyne-containing electron-deficient alkenes with organoboron reagents to provide five- or six-membered rings with exo tri- or tetra-substituted alkenes. The opposite stereoselectivity to that for the alkyne-aldehyde cyclization using the same reagents would result from palladacycle-forming oxidative addition of the substrates to the Pd⁰ catalyst followed by transmetalation with the boron reagents, protonation, and reductive elimination. The functional group compatibility, availability, stability, and non-toxicity of the reagents, and the fact that no additives are needed make the process more practical than the Ni⁰-catalyzed cyclization with organozinc reagents.     

Palladium-catalyzed oxidative carbonylation of alkyl and aryl indium reagents with CO under mild conditions

CO now can react with organoindium reagents. A novel palladium-catalyzed oxidative carbonylation reaction of organoindium reagents by CO gas with desyl chloride as oxidant was developed in supplementation with the classical methods for preparation of carboxylic acid derivatives. Primary, secondary alkyl indium reagents with beta-hydrogens and aryl indium reagents were suitable substrates, and the reaction could be carried out at 60 degrees C under 50 psi CO. Carbonylation of alkyl indium reagents can occur smoothly without additional base. Although the indium reagents were prepared from corresponding Grignard reagents (at low temperature), they displayed full compatibility with various functional groups under the protic reaction conditions. Preliminary mechanistic studies including stoichiometric and catalytic reaction examination provided evidence to support the operation of the mechanism consisted of oxidative addition of deslyl chloride to Pd(0) and quick tautomerization to give a palladium enolate species II (ROPdCl), displacement of the enolate group in II by R(2)OH, followed by CO insertion to give alkoxycarbonyl palladium complex V, which undergoes transmetalation with R(1)(3)In and reductive elimination to afford the product and a Pd(0) species. In this mechanism, the alkoxycarbonyl group was transferred to the palladium center prior to the alkyl group, different from traditional ways initiated from oxidative addition of alkyl halides to a Pd(0) species.