Hypervalent iodine-mediated gem-difluorination of vinyl halides enabled by exclusive 1,2-halo migration

β-Difluorinated alkyl halides are of significant value in the modular synthesis of gem-difluorinated molecules. An exclusive 1,2-halo migratory gem-difluorination of vinyl halides with in situ-generated PhIF_2·HF is described. This protocol provides a general and practical approach towards a wide variety of β-difluorinated alkyl bromides. Both α-and β-bromoalkyl alkenes are suitable substrates, leading to two distinct types of products. The extension of this protocol to vinyl chloride and iodide are also feasible.The synthetic versatility of this method has been highlighted by the late-stage modification of complex small molecules and further transformations of the β-difluorinated alkyl halides to valuable CF_2-containing compounds.     

Molecular mechanics on bonding and non-bonding interactions in (atom@C_(60))

The interactions between the embedded atom X (X=Li,Na,K,Rb,Cs; F,Cl,Br,I) and C60cage in the endohedral-form complexes (X@C60) are calculated and discussed according to molecular mechanics from the point of view of the bonding and non-bonding.It is found from the computational results that for atoms with radii larger than Li's,their locations with the minimum interaction in (X@C60) are at the cage center,while atom Li has an off-center location with the minimum interaction deviation of-0.05 nm,and the cage-environment in C60 can be regarded as sphero-symmetry in the region with radius r of ~0.2 nm.It is shown that the interaction between X and C60 cage is of non-bonding characteristic,and this non-bonding interaction is not purely electrostatic.The repulsion and dispersion in non-bonding interactions should not be neglected,which make important contribution to the location with minimum interaction of X,at center or off center.Some rules about the variations of interactions with atomic radii have been ob     

Acceleration of carbon-13 spin-lattice relaxation times in amino acids by electrolytes

A series of amino acids and carboxylic acids were determined by C NMR spectroscopy. 13 The results showed that addition of 3M MgCl2 led to the C NMR integral area of samples being 13 well proportional to number of carbon atoms that produce the particular signal with reliability over 95%. Measurements of C spin-lattice relaxation times (T1’s) are reported for a number of amino 13 acids. T1’s of all the carbons in amino acids generally tend to decrease with the increase of the c…     

Photopromoted Carbonylation of Alkyl Halides Under Ambient Conditions

Photopromoted carbonylation of alkyl halides with carbon monoxide can be carried out under ambient conditions with non-precious transition metal complexes(such as cobalt complexes) catalysts.Our preliminary work sowed that alkyl halides can be transformed into alkene and alkane directly under irradiation,but the esters can not be transformed.It is assumed that the carbonylation of alkyl halides may be proceeded in two ways.     

Effects of Heat Treatment on the Crystallization Behavior of Poly(3-alkylthiophenes)

IntroductionPoly( 3- alkylthiophenes) ( P3ATs) ,as a newkind of soluble,fusible and processable conductivepolymers,have attracted a great interest and muchattention ofchemistsand physicists[1,2 ] . Ithas beenwidely accepted that P3ATs can form similarlayered structures with alkyl side chains beingoriented in the lateral a- axis direction[3— 6] .Moreover,when the number of the carbon atoms inthe alkyl side chains is more than1 0 ,some orderlyarrangements of the side chains will occur between…     

不同温度下α-氨基酸在CTAB溶液中的体积及折光率的变化

Densities(ρ)and refractive indices(nD)of glycine(Gly),DL-alanine(Ala),DL-valine(Val)(0.02,0.04,0.06,0.08,and 0.10 mol·L-1)in 0.005 and 0.008 mol·L-1 aqueous cetyltrimethylammonium bromide(CTAB)have been measured at 298.15,303.15,308.15,and 313.15 K.The density data have been utilized to calculate apparent molar volumes(φv),partial molar volumes(φ0v),at infinite dilution and partial molar volumes of transfer φ0v(tr)of amino acids.The refractive index data have been used to calculate molar refractivity(RD)of amino acids in aqueous cetyltrimethylammonium bromide.It has been observed that φ0v varies linearly with increasing number of carbon atoms in the alkyl chain of amino acids,and hence,was split to get contributions from the zwitterionic end groups(NH 3,COO-)and methylene group(CH2)of the amino acids.The behaviour of these parameters has been used to investigate the solute-solute,solute-solvent interactions and the effect of cetyltrimethylammonium cation on these interactions.     

Methane oxidative carbonylation catalyzed by rhodium chalcogen halides over carbon supports

Gas phase carbonylation of methane is studied in the presence of molecular oxygen over pure carbon carriers and carbon supported rhodium chalcogen halides. Activated carbons and fullerene blacks have been used as carbon supports. XPS and IR-spectroscopy data show the formation of rhodium chalcogen halides in solids prepared by different methods. We have found that the productivity of acetic acid by carbon supported rhodium chalcogen halides depends strongly on the carbon carrier and the method of the catalyst preparation. Namely, the catalyst with highest productivity for the acetic acid is prepared by synthesizing the rhodium chalcogen halide over the carbon support followed by thermal destruction. We have also found that rhodium chalcogen halides over activated carbons are more active compared with fullerene supported catalysts.     

有机磷化合物的研究 VIII. 酸性有机磷化合物的气相色谱

Acidic organophosphorus compounds may be identified by GLC via their methyl esters, usually prepared from diazomethane. The wide applications of this mthod are, however, limited by the toxicity of diazomethane. Tetramethyl ammonium hydroxide in methanol solution reacted rapidly with acidic organophosphorus compounds at room temperature to form tetramethyl ammonium salts, which were then converted to the corresponding methyl esters by pyrolysis at 300-350 deg.C. A simple and convenient method for separation and identification of various types of acidic phosphates, phosphonates and phosphinates by GLC has been developed. The GLC behaviours of phosphoric acid dialkyl esters, mono-esters of phenyl-and cyclohexyl-phosphonic acids as well as dialkylphosphinic acids can be represented by corrected retention time (t'R) which correlates linearly with the number of carbon atoms of the alkyl groups in these organophosphorus compounds. The influence of number of carbon atoms and isomerization of alkyl group on t'R values and retention index (I) calculated by Kovats equation was discussed. As shown by our experiments the change in retention index (ΔI) in the homologous series of phosphoric acid dialkyl esters is nearly a constant on lengthening the alkyl group of the esters with methylene linkages.     

甾体磷酰胺类缀合物在电喷雾质谱中的裂解特征

Novel steroidal phosphoramidate conjugates of 3'-azido-2',3'-dideoxythymidine(AZT)and amino acid esterswere synthesized and determined by positive and negative ion electrospray ionization mass spectrometry.The MSfragmentation behaviors of the steroidal phosphoramidate conjugates have been investigated in conjunction withtandem mass spectrometry of ESI-MS/MS.There were three characteristic fragment ions in the positive ion ESImass spectra,which were the Na adduct ions with loss of steroidal moiety,amino acid ester moiety from pseudomolecular ion(M Na)~ ,and the phosphoamino acid methyl ester Na adduct ion by α-cleavage of the phosphora-midate respectively.The main fragment ions in negative ion ESI mass spectra were the ion(M-HN_3)~-,the ion(M-AZT-H)~-,and the ion(M-steroidal moiety-H)~- besides the pseudo molecular ion(M-H)~-.Thefragmentation patterns did not depend on the attached amino acid ester moiety.     

Theoretical Studies on the Molecular Structures and Thermodynamic Properties of Polychlorinated Acenaphthylenes

Geometric structures of 135 polychlorinated acenaphthylene (PCAC) molecules were optimized using density functional theory (DFT) at the B3LYP/6-311G** level and some thermodynamic properties of them in the ideal gas state were calculated. The relations of these thermodynamic properties with the number and position of chlorine atoms were also explored, from which the relative stability of PCAC congeners was theoretically proposed according to the magnitude of the relative standard Gibbs free energy of formation (△r,fGθ). The results show that all PCAC isomers have planar geometric configuration. There exists intramolecular Cl···Cl weak interaction in some PCAC molecules. The change of △fHθ and fGθ of most stable PCAC isomers with increasing the number of chlorine atoms is different from that in the least stable PCAC congeners. The values of fHθ and fGθ for PCAC isomers with the same number of chlorine atoms show a strong dependence on the position of chlorine atoms and the relative stability of PCAC congeners has close relation with the intramolecular Cl···Cl nuclear repulsive interaction.     

Retention behavior of a homologous series and positional isomers of aliphatic amino acids in hydrophilic interaction chromatography

The retention behavior of several series of free α‐ and ω‐amino acids and positional isomers of amino pentanoic acid in the hydrophilic interaction chromatography mode (HILIC) was studied. The study was carried out on three stationary phases followed by post‐column derivatization with fluorescence detection in order to describe the retention mechanism of the tested amino acids. The effect of chromatographic conditions including acetonitrile content in the mobile phase, mobile phase pH (ranging from 3.5 to 6.5) and concentration of buffer in the mobile phase was investigated. The effect of the number of carbon atoms (n_C) in aliphatic chains of the individual homologue of α‐ and ω‐amino acids and the logarithm of the partition coefficient (logD) on retention was also a part of the presented study. A good correlation (r > 0.98) between the logk and logD values of amino acids or n_C, respectively, was observed. The described linear relationships were subsequently applied to predict the retention behavior of individual members of the homologous series of amino acids and to optimize the mobile phase composition in HILIC. The obtained results confirmed that the retention mechanism of α‐amino acids, ω‐amino acids and positional isomers of amino acids was based on the logD values and the number of carbon atoms in the aliphatic chains of amino acids. The elution order of ω‐amino acids and positional isomers of amino pentanoic acid was strongly dependent on the mobile phase pH in the investigated range whereas the retention factors of all α‐amino acids remained essentially unchanged on all tested stationary phases.     

Enantioselective Organocatalytic Addition of Oxazolones to 1,1‐Bis(phenylsulfonyl)ethylene: A Convenient Asymmetric Synthesis of Quaternary α‐Amino Acids

A new, easy, and highly enantioselective method for the synthesis of quaternary α‐alkyl‐α‐amino acids based on organocatalysis is reported. The addition of oxazolones to 1,1‐bis(phenylsulfonyl)ethylene is efficiently catalyzed by simple chiral bases or thioureas. The reaction affords α,α‐disubstituted α‐amino acid derivatives with complete C4 regioselectivity and with excellent yields and enantioselectivities. This methodology is complementary to previously reported enantioselective approaches to quaternary α‐amino acids and allows the synthesis of α‐phenyl‐α‐alkyl‐α‐amino acids and α‐tert‐butyl‐α‐alkyl‐α‐amino acids. It has distinct advantages in terms of operational simplicity, enviromentally friendly conditions, and suitability for large‐scale reactions.     

α-氨基酸与氯化铷在水溶液中焓相互作用参数

The mixing enthalpies of aqueous heavy rare alkali metal chloride RbC1 solutions with aqueous α-amino acid (Loglycine, L-alanine and α-aminobutyric acid) solutions, as well as the dilution enthalpies of RbC1 and α-amino acid solutions in pure water had been measured at 298.15K. The transfer enthalpies of RbCI from pure water to aqueous α-amino acid solutions could be obtained from these data. The enthalpic pair interaction parameters of RbC1 with α-amino acid in water have been evaluated according to the McMillan-Mayer theory and discussed in terms of the electrostatic interaction, structure interaction and Savage-wood group additivity mode.     

The Chemical Ionization of Organic Compounds. 2nd Communication. Linear Alkyl Halides

The chemical ionization spectra of linear alkyl halides with up to nine carbon atoms have been studied using water as protonating agent. An alkyl ion with the same number of carbon atoms as the halide is produced. With more than six carbon atoms in the chain, fragmentation becomes important. The results show that excited hydronium ions participate as intermediates and the fragments of the resulting alkyl ions have branched structures.     

Enthalpy of interaction of some electrolytes with 2-methyl-2-butanol in wate at 25°C

Enthalpies of mixing in water of 2-methyl-2-butanol with several electrolytes (alkali-metal halides, tetra-n-alkylammonium bromides, Ph₄PCl, Ph₄AsCl and NaPh₄B) have been determined by flow microcalorimetry at 25°C. Enthalpic pair interaction coefficients, h_NE, of the virial expansion of the excess enthalpy were calculated. All coefficients are positive and increase as the anionic size increases in anionic series of alkali-metal halides. A linear correlation between h_NE and the number of carbon atoms in the apolar group of R₄NBr is observed. For alkali-metal halides coefficients h_NE depend mainly on the partial desolvation of halides, and for hydrophobic electrolytes both the partial desolvation of halide ions and hydrophobic interaction are the leading factors in the value of h_NE.     

Enantioselective Synthesis of Quaternary α‐Amino Acids Enabled by the Versatility of the Phenylselenonyl Group

A novel Cinchona alkaloid‐catalyzed enantioselective conjugate addition of α‐alkyl substituted α‐nitroacetates to phenyl vinyl selenone was developed. The resulting enantio‐enriched α,α‐dialkyl substituted α‐nitroacetates were subsequently converted to various cyclic and acyclic quaternary α‐amino acids, taking advantage of the rich functionalities of the resulting Michael adducts. Novel protocols allowing chemoselective reduction of phenyl selenone to phenyl selenide and reduction of alkyl phenyl selenones to alkanes are also reported.     

The synthesis and coordination properties of new macrocyclic polyethers

A new type of macrocyclic polyethers has been synthesized. It consists of an azacrown ether as mother ring, e.g. 1,7-dioxa-4,10-diaza-cyclododecane (1a) or 1,7,10,16-tetraoxa-4,13-diazacycloocatadecane (1b), and two side chains attached on the two nitrogen atoms of 1a or 1b. A number of these new crown ethers are obtained by alkylation of the two secondary amino groups of 1a or 1b with corresponding halides, BrCH₂(CH₂OCH₂)_nCH₂OR, in the presence of potassium carbonate. The crown-alkali metal complex thus obtained is hydrolyzed by acid. In order to obtain pure crown ether the reaction mixture is treated with tetramethylammonium hydroxide and followed by solvent extraction. The ability of complexing alkali cations of macrocyclic polyethers in terms of the equilibrium constant have been studied by the method of solubilities of salts in chloroform. It is shown that the size of the mother ring, the number of oxygen atoms either in the ring or in the side-chains, and the ionic radius of the alkali metal are the factors governing the stability of the metal complexes. Most of these new crown ethers possess high ability for alkali metal complexation some of them, such as N,N′- di-β-methoxyethyl-1,7-dioxa-4,10-diaza-cyclododecanc (13a), possesses higher selectivity for Na+ and K+ ions than 18-crown-6- and 4,4′(5′)-dimethylbenz-30-crown-10.     

Bispalladacycle‐Catalyzed Michael Addition of In Situ Formed Azlactones to Enones

The development and further evolution of the first catalytic asymmetric conjugate additions of azlactones as activated amino acid derivatives to enones is described. Whereas the first‐generation approach started from isolated azlactones, in the second‐generation approach the azlactones could be generated in situ starting from racemic N‐benzoylated amino acids. The third evolution stage could make use of racemic unprotected α‐amino acids to directly form highly enantioenriched and diastereomerically pure masked quaternary amino acid products bearing an additional tertiary stereocenter. The step‐economic transformations were accomplished by cooperative activation by using a robust planar chiral bis‐Pd catalyst, a Brønsted acid (HOAc or BzOH; Ac=acetyl, Bz=benzoyl), and a Brønsted base (NaOAc). In particular the second‐ and third‐generation approaches provide a rapid and divergent access to biologically interesting unnatural quaternary amino acid derivatives from inexpensive bulk chemicals. In that way highly enantioenriched acyclic α‐amino acids, α‐alkyl proline, and α‐alkyl pyroglutamic acid derivatives could be prepared in diastereomerically pure form. In addition, a unique way is presented to prepare diastereomerically pure bicyclic dipeptides in just two steps from unprotected tertiary α‐amino acids.     

Copper‐Catalyzed Decarboxylative Radical Silylation of Redox‐Active Aliphatic Carboxylic Acid Derivatives

A decarboxylative silylation of aliphatic N ‐hydroxyphthalimide (NHPI) esters using Si−B reagents as silicon pronucleophiles is reported. This C(sp³)−Si cross‐coupling is catalyzed by copper(I) and follows a radical mechanism, even with exclusion of light. Both primary and secondary alkyl groups couple effectively, whereas tertiary alkyl groups are probably too sterically hindered. The functional‐group tolerance is generally excellent, and α‐heteroatom‐substituted substrates also participate well. This enables, for example, the synthesis of α‐silylated amines starting from NHPI esters derived from α‐amino acids. The new method extends the still limited number of C(sp³)−Si cross‐couplings of unactivated alkyl electrophiles.