Fluorinated tellurium(IV) azides and their precursors

The perfluoroaryl tellurolates C₆F₅TeLi (1) and 4-CF₃C₆F₄TeLi (2) were prepared. These intermediates were identified by NMR spectroscopy and may form, depending on the reaction conditions, either the corresponding ditellanes C₆F₅TeTeC₆F₅ (3) and CF₃C₆F₄TeTeC₆F₄CF₃ (4) by subsequent oxidation, or in the case of 1, a telluranthrene (C₆F₄Te)₂ (5) by reaction with itself. The halogenation products of 5, ( C₆F₄Te)₂F₄ (6), (C₆F₄Te)₂Cl₄ (7), (C₆F₄Te)₂Br₄ (8), as well as the azidation product (C₆F₄Te)₂(N₃)₄ (9) were synthesized. Furthermore, in pursuit of our recent work on tellurium azides, the syntheses and properties of R₂Te(N₃)₂ (R=CF₃ (10), C₆F₂H₃ (11)) and RTe(N₃)₃ (R=CF₃ (12) and C₆F₅ (13)) are reported. The crystal structures of CF₃C₆F₄TeTeC₆F₄CF₃ (4), (C₆F₄Te)₂Br₄ (8), and (C₆F₂H₃)₂Te(N₃)₂ (11) were determined.     

Odd/even effect in the chain length on the enthalpy of micellization of gemini surfactants in aqueous solution

The micellization properties of cationic symmetric gemini surfactants, [CmH(2m+1)(CH3)2N(CH2)6N(CH3)2CmH(2m+1)]Br2 (designated as CmC6CmBr2, with m = 7, 8, 9, 10, 11, 12, and 16), has been investigated by isothermal titration microcalorimetry. The critical micelle concentration (CMC) and enthalpy of micellization (DeltaHmic) were determined from calorimetric titration curves. The linear decreasing of log CMC with increasing the length of the hydrophobic chain is consistent with an increase in the hydrophobicity of the alkyl chain. Interestingly, with increasing the length of the alkyl chain, the DeltaHmic values of the surfactants with even numbered alkyl chains vary from endothermic to exothermic, whereas the DeltaHmic values of the surfactants with odd numbered alkyl chains are all endothermic and tend to become more endothermic. The pronounced even/odd effect in DeltaHmic is discussed with respect to the "donor-acceptor" interaction.     

Studies toward labeling cytisine with [11C]phosgene: rapid synthesis of a delta-lactam involving a new chemoselective lithiation-annulation method

With the aim of the radiolabeling of cytisine, a potent agonist of nicotinic receptors, with [(11)C]phosgene, the rapid synthesis of a lactam model of our target has been studied. The key step of the delta-lactam formation is a new chemoselective lithiation-annulation method, under high dilution, of a suitable piperidinylcarbamoyl chloride. This precursor was obtained from (2-hydroxyethyl)piperidine in a linear synthetic sequence involving a Corey-Fuchs olefination of the corresponding aldehyde, followed by a selective reduction, using a diimide equivalent, of an iodoalkyne into a (Z)-iodopropene piperidine. This alkene served as main precursor to study the cyclization according to several procedures using phosgene as the required carbonylating reagent.     

Syntheses and properties of dithia‐tetrahomodiaza‐calix[4]arenes bridged by cystine unit

Dithia‐tetrahomodiaza‐calix[4]arenes were synthesized by the cyclization reactions of bis(3‐(chloro‐methyl)‐2‐hydroxyphenyl)sulfide with cystine peptides in moderate yields. Conformational analysis of the macrocycles by using nmr spectroscopy reveled that the cyclophanes adopt a cone‐like form as a preferable conformation and the cystine bridge moiety is incorporated in the cavity. The calixarene analogs can extract transion metals such as Zn²⁺ and Cu²⁺ ions from an aqueous phase into chloroform.     

Photokatalytische Systeme. XLIV. Über das Intervalence-Charge-Transfer-Verhalten von Ionenpaarassoziaten des Octacyanomolybdats

Photocatalytic Systems. XLIV. On the Intervalence Charge Transfer Behaviour of Ion Pairs of Octacyanomolybdate [Mo(CN)₈]^4? ions are forming coloured ion pairs with Fe^III, Cu^II, U^VIO₂, and V^IVO, the long-wavelength absorption band of which could be assigned to an intervalence charge-transfer transition. From the solvent dependence of the IT band, interionic distances could be estimated.     

Er2S[SiO4]: Ein Erbiumsulfid‐ortho‐Oxosilicat mit ungewöhnlicher Sulfidionen‐Koordination

During the reaction of cadmium sulfide with erbium and sulfur in evacuated silica ampoules pink lath‐shaped crystals of Er₂S[SiO₄] occur as by‐product which were characterized by X‐ray single crystal structure analysis. The title compound crystallizes orthorhombically in the space group Cmce (a = 1070.02(8), b = 1235.48(9), c = 683.64(6) pm) with eight formula units per unit cell. Besides isolated ortho‐oxosilicate units [SiO₄]^4?, the crystal structure contains two crystallographically independent Er³⁺ cations which are both eightfold coordinated by six oxygen and two sulfur atoms. The sulfide anions are surrounded by four erbium cations each in the shape of very distorted tetrahedra. These excentric [SEr₄]¹⁰⁺ tetrahedra build up layers according to by vertex‐ and edge‐connection. They are piled parallel to (010) and separated by the isolated ortho‐oxosilicate tetrahedra.     

Rapid biomass analysis

New, rapid, and inexpensive methods that monitor the chemical composition of corn stover and corn stover-derived samples are a key element to enabling the commercialization of processes that convert stover to fuels and chemicals. These new techniques combine near infrared (NIR) spectroscopy and projection to latent structures (PLS) multivariate analysis to allow the compositional analysis of hundreds of samples in 1 d at a cost of about $10 each. The new NIR/PLS rapid analysis methods can also be used to support a variety of research projects that would have been too costly to pursue by traditional methods.     

Stereospecific rearrangements during the synthesis of pyrrolidines and related heterocycles from cyclizations of amino alcohols with vinyl Sulfones

Conjugate additions of amino alcohols derived from alpha-amino acids to vinyl sulfones, followed by N-benzylation, chlorination, and intramolecular alkylation, provide a convenient route to substituted pyrrolidines. The process is accompanied by the stereospecific rearrangement of substituents from the alpha-position of the amine to the beta-position of the product and takes place via the corresponding aziridinium ion intermediates. Another type of rearrangement was observed during the reaction of (2-piperidine)methanol or 2-(2-piperidine)ethanol with phenyl trans-1-propenyl sulfone, in which the methyl group appears to migrate from the beta- to the alpha-position of the sulfone moiety. This process involves the isomerization of phenyl trans-1-propenyl sulfone to phenyl 2-propenyl sulfone by the addition-elimination of catalytic benzenesulfinate anion to the former vinyl sulfone, followed by conjugate addition of the amino group to the latter sulfone. Chlorination and intramolecular alkylation then afford the corresponding rearranged indolizidine and quinolizidine derivatives, respectively.     

Lewis base activation of lewis acids. Addition of silyl ketene acetals to aldehydes

The weak Lewis acid silicon tetrachloride can be activated by catalytic amounts of the chiral bisphosphoramide (R,R)-3 to form a highly reactive, chiral trichlorosilyl cation which is an extremely effective promoter of aldol addition reactions between aldehydes and silyl ketene acetals. The tert-butyldimethylsilyl ketene acetal of methyl acetate adds nearly instantaneously to aromatic and olefinic aldehydes as well as aliphatic aldehydes (albeit more slowly) with excellent enantioselectivity. The homologous tert-butyldimethylsilyl ketene acetal of tert-butyl propanoate adds with nearly exclusive anti diastereoselectivity to a similar range of aldehydes also with excellent enantioselectivity. The origin of the slower reaction rate with aliphatic aldehydes is revealed to be the formation of chlorosilyl ether adducts.     

Oxidation of organic sulfides by vanadium haloperoxidase model complexes

In addition to halide oxidation, the vanadium haloperoxidases are capable of oxidizing sulfides to sulfoxides. Four vanadium complexes with tripodal amine ligands, K[VO(O(2))(heida)] (1), VO(2)(bpg) (2), K[VO(2)(ada)] (3), and K(2)[VO(O(2))(nta)] (4), previously shown to perform bromide oxidation (Colpas, G. J.; Hamstra, B. J.; Kampf, J. W.; Pecoraro, V. L. J. Am. Chem. Soc. 1996, 118, 3469-3477), have now been shown to oxidize aryl alkyl sulfides to the corresponding sulfoxides. The oxidation was observed by the disappearance of thioanisole's ultraviolet absorption at 290 nm, by the change in the aromatic region of the (1)H NMR spectrum of the sulfides, and by changes in the complexes' (51)V NMR spectra. The amount of methyl phenyl sulfide oxidized in 3 h was 1000 equiv (per metal complex). The oxidation product is almost exclusively sulfoxide, with very little sulfone (less than 3% over a 3 h experiment) formed. This is consistent with an electrophilic oxidation mechanism, as had been proposed for oxidation of bromide by 1-4. The rate was found to be first order in substrate concentration, similar to the rate law observed for bromide oxidation. Unlike the bromide oxidation, the equivalent of acid required for peroxovanadium complex activation is not consumed. The complexes 1-4 are not reactive with styrene or cyclooctene. The relevance of these reactions to the mechanism of the vanadium haloperoxidases and, more generally, peroxovanadium oxygenation of sulfides will be discussed.