The synthesis of N-substituted ketimines from oxazirdines

N-Unsubstituted diaryl, alkyl aryl and dialkyl ketimines are prepared in good yield at ambient temperature by the reaction of KOBu^t on oxaziridines having an α-hydrogen atom on the N-alkyl substituent; the mechanism and stereochemistry of the reaction are discussed.     

Deoxygenation of sulfoxides, selenoxides, telluroxides, sulfones, selenones and tellurones with Mg-MeOH

The deoxygenation of a variety of sulfoxides, selenoxides, telluroxides, sulfones, selenones and tellurones has been reported with Mg-MeOH at room temperature in nearly quantitative yields. The deoxygenation is proposed to proceed by SET from Mg to the substrate.     

A new macrocyclic polystyrene-based sensor for chromium (III) ions

A new tetradentate dihydrogen perchlorate macrocyclic ligand (2,4,9,11-tetraphenyl-1,5,8,12-tetraazacyclotetradeca-1,4,8,11-tetraene dihydrogen perchlorate) was prepared and characterised. The macrocycle behaves as a selective chelating ion-exchanger for some metal ions. The polystyrene-based membrane electrode is found to exhibit quite promising selectivity for Cr3+ ions. It can be used to estimate chromium concentrations in the range 3.16x 10(-6)-1.00x10(-1) M with a near-Nernstian slope of 17.5 mV per decade of concentration between pH 3.0 to 6.5. The electrode is found to possess a fast response time of 15 s and was used over a period of three months with good reproducibility (s = +/- 0.3 mV). The selectivity coefficient values for mono-, di- and trivalent cations indicate excellent selectivity for Cr3+ ions over a large number of other cations. Anions such as Cl- and SO4(2-) do not interfere and the electrode also works satisfactorily in a mixed organic-water solution. The sensor has been used as an indicator electrode for the potentiometric titration of Cr3+ with EDTA. The practical utility of the membrane sensor has also been demonstrated in solutions contaminated with detergents (CTAB and SDS). Above all, the membrane sensor has been very successfully used to determine Cr3+ in some foods.     

New ruthenium-based protocol for cleavage of terminal olefins to primary alcohols: improved synthesis of a bicyclic nucleoside

A new protocol for the oxidative cleavage of terminal alkenes to give exclusively primary alcohols in high yields is introduced. The protocol is based on RuO4-mediated dihydroxylation, NaIO4-mediated diol cleavage, and NaBH4-mediated reduction, but the introduction of a reducing step before the diol cleavage removes the formation of byproducts and improves the yield significantly. The new protocol has been developed and used for the improved preparation of a [3.2.0]bicycloarabinonucleoside with important potential in antisense and antigene technology.     

Thermal studies of some aryloxides of titanium(IV)

Thermal behaviour of aryloxides of titanium(IV) of composition TiCl_n(OAr)_4?n (wheren=0→3 and OAr=OC₆Bu^t-4, OC₆H₄OMe-4 and OC₆H₂-Bu ₂ ^t -2,6?Me-4) has been studied by DTA and TG analysis. Multiple decomposition steps have been indicated by thermal weight losses which are both exothermic and endothermic as shown by DTA curves. Based upon the total % loss in weight; during entire decomposition titanium dioxide has been found to be the final residue in each case.     

Synthesis and characterization of polyesters containing heterocyclic thiaxanthone units

Several polyesters containing thiaxanthone rings were prepared from 2,7-dichloroformylthiaxanthone-5,5′-dioxide ( IVa ), 2,8-dichloroformylthiaxanthone-5,5′-dioxide ( IVb ), and bisphenols by solution polycondensation. The 2,8-diethoxycarbonylthiaxanthone-5,5′-dioxide ( V ) was prepared and characterized by spectral methods to confirm the formation of 2,8-thiaxanthonedicarboxylic acid-5,5′-dioxide ( IVb ). Prior to polymer synthesis two model compounds,2,7-diphenoxycarbonylthiaxanthone-5,5′-dioxide (MDE-1) and 2,8-diphenoxycarbonylthiaxanthone-5,5′-dioxide (MDE-2), were synthesized and characterized by spectral methods. The polyesters were obtained in 62–78% yield and had inherent viscosities in the range 0.42–0.90 dL/g. The effect of thiaxanthone rings on solubility, crystallinity, and thermal stability of the polyesters are also discussed. The polyesters have decomposition temperatures in the range 372–438°C.     

Products active on mosquitoes,IV: Synthesis and biological activity of 8-propargyloxy-3,7-dimethyl-2,6-octadienyl/6-octenyl ethers

Summary A series of 8-proparglyoxy-3,7-dimethyl-2,6-octadienyl and 8-propargyloxy-3,7-dimethyl-6-octenyl ethers were prepared from 8-hydroxygeranyl and 8-hydroxycitronellyl ethers, respectively. Almost all compounds showed high toxicity toCulex quinquefaciatus larvae at 1 mgl^–1 dose level.

---

Gegen Mücken aktive Produkte, 4. Mitt.: Synthese und biologische Aktivität von 8-Propargyloxy-3,7-dimethyl-2,6-octadienyl/6-octenyl-ethern

Zusammenfassung Eine Reihe von 8-Propargyloxy-3,7-dimethyl-2,6-octadienyl- und 8-propargyloxy-3,7-dimethyl-6-octenyl-ethern wurden aus 8-Hydroxygeranyl- bzw. 8-Hydroxycitronellyl-ethern hergestellt. Fast alle Verbindungen zeigten hoch Toxizität gegenüber Larven vonCulex quinquefaciatus in einer Dosierung von 1 mgl^–1.

     

The stereochemistry of guggulsterol-1

The steroechemistry of guggulsterol-1, a component of the exudate of $\text{Commiphora}$$\text{mukul}$, is shown to be 20(R), 22(R)($\text{3}$).     

Stereoselective reductase-catalysed deoxygenation of sulfoxides in aerobic and anaerobic bacteria

Direct and indirect evidence, of unexpected stereoselective reductase-catalysed deoxygenations of sulfoxides, was found. The deoxygenations proceeded simultaneously, with the expected dioxygenase-catalysed asymmetric sulfoxidation of sulfides, during some biotransformations with the aerobic bacterium Pseudomonas putida UV4. Stereoselective reductase-catalysed asymmetric deoxygenation of racemic alkylaryl, dialkyl and phenolic sulfoxides was observed, without evidence of the reverse sulfoxidation reaction, using anaerobic bacterial strains. A purified dimethyl sulfoxide reductase, obtained from the intact cells of the anaerobic bacterium Citrobacter braakii DMSO 11, yielded, from the corresponding racemates, enantiopure alkylaryl sulfoxide and thiosulfinate samples.     

Copper(II), nickel(II), cobalt(II) and zinc(II) complexes of 2-[2-(6-methylbenzothiazolyl)azo]-5-dimethylaminobenzoic acid: synthesis,spectral, thermal and molecular modelling studies

Complexes of copper(II), nickel(II), cobalt(II), and zinc(II) with 2-[2-(6-methylbenzothiazolyl)azo]-5-dimethylaminobenzoic acid have been prepared and characterized by elemental analysis, vibrational spectra, magnetic susceptibility measurements, conductance measurements and e.p.r. spectra. Stability constants have been evaluated potentiometrically. Electronic spectra, magnetic susceptibility measurements and molecular modeling studies support a distorted square planar geometry around the metal ions. Vibrational spectra indicate the coordination of the azo group, nitrogen of benzothiazole, the carboxylate anion and the acetate ion on complexation with the metal ion. All complexes are found to be monomers. The stability of the complexes follow the order: copper(II) > nickel(II) > cobalt(II) > zinc(II).