Synthesis of 4H-3,3a-dihydrothiazolo[4,3-b]quinazolines

Regiospecific synthesis of 4H-3,3a-dihydrothiazolo[4,3-b]quinazolines and 7-methyl-4H-3,3a-dihydrothiazolo[4,3-b]quinazolines IVa and IVb is described. The N-substituted thiazolidinecarboxylic acids Ia and Ib were converted to the corresponding acid chlorides, IIa and IIb but neither reacted with silver trifluoromethanesulphonate. The carboxylic acids Ic and Id were however, decarboxylated to the corresponding iminium ions using phosphorus oxychloride and these afforded the nitroamines IIIa and IIIb. Reductive cyclisation led to the quinazolines IVa and IVb.     

Polycyclic nitrogen compounds. Part II. Tricyclic quinoxalinones and their 4- or 6-aza analogues

1,2,3,3a-Tetrahydro-9-nitropyrrolo[1,2-α]quinoxalin-4-one and 7,8,9,10-tetrahydro-3-nitropyrido[1,2-α]quin-oxalin-6-one (V-VI) were reduced and deaminated to give new parent tricyclic quinoxalinone skeletons I-II. The latter compounds were identical with the tricycles obtained by an unambiguous independent synthesis. New 6-aza-1,2,3,3a-tetrahydropyrrolo[1,2-α]quinoxalin-4-one (III) and 4-aza-7,8,9,10-tetrahydropyrido[1,2-α]-quinoxalin-6-one (IV) were prepared by selective hydrogen transfer reductive cyclisation of esters of N-(2-nitro-3-pyridyl)pyrrolidine-2-carboxylic acid and N-(2-nitro-3-pyridyl)piperidine-2-carboxylic acid (Xb and XIb) respectively.     

Polycyclic nitrogen compounds. Part I. Synthesis of new heterotricyclic quinoxalinones with bridgehead nitrogen atoms

New tricyclic quinoxalinone skeletons with a fully-reduced ring ‘C’ -1,2,3,3a-tetrahydropyrrolo[1,2-α]quin-oxalin-4-one (I-II) and 7,8,9,10-tetrahydropyrido[1,2-α]quinoxalin-6-one (III-IV) derivatives were obtained by selective hydrogen transfer reductive cyclisation of N-(2-nitrophenyl)pyrrolidine-2-carboxylic acid esters and N-(2-nitrophenyl)piperidine-2-carboxylic acid esters (VIa,b and VIIIa,b), respectively.     

Capillary array isoelectric focusing with laser-induced fluorescence detection: milli-pH unit resolution and yoctomole mass detection limits in a 32-channel system

We report a multiplexed capillary electrophoresis system employing an array of 32 capillaries with a micromachined sheath-flow cuvette as the detection chamber. The sample streams were simultaneously excited with a 473-nm laser beam, and the fluorescence emission was imaged on a CCD camera with a pair of doublet achromat lens. The instrument produced mass detection limits of 380 ± 120 yoctomoles for fluorescein in zone electrophoresis. Capillary isoelectric focusing of fluorescent standards produced peaks with an average width of 0.0029 ± 0.0008 pH. Capillary coating stability limits the reproducibility of the analysis.     

Probing the interaction of hydrogen chloride with low-temperature water ice surfaces using thermal and electron-stimulated desorption

The interaction and autoionization of HCl on low-temperature (80-140 K) water ice surfaces has been studied using low-energy (5-250 eV) electron-stimulated desorption (ESD) and temperature programmed desorption (TPD). There is a reduction of H(+) and H(2)(+) and a concomitant increase in H(+)(H(2)O)(n=1-7) ESD yields due to the presence of submonolayer quantities of HCl. These changes are consistent with HCl induced reduction of dangling bonds required for H(+) and H(2)(+) ESD and increased hole localization necessary for H(+)(H(2)O)(n=1-7) ESD. For low coverages, this can involve nonactivated autoionization of HCl, even at temperatures as low as 80 K; well below those typical of polar stratospheric cloud particles. The uptake and autoionization of HCl is supported by TPD studies which show that for HCl doses ≤0.5 ± 0.2 ML (ML = monolayer) at 110 K, desorption of HCl begins at 115 K and peaks at 180 K. The former is associated with adsorption of a small amount of molecular HCl and is strongly dependent on the annealing history of the ice. The latter peak at 180 K is commensurate with desorption of HCl via recombinative desorption of solvated separated ion pairs. The activation energy for second-order desorption of HCl initially in the ionized state is 43 ± 2 kJ/mol. This is close to the zero-order activation energy for ice desorption.     

Polycyclic nitrogen compounds. Part iii. Synthesis of 3,3a-dihydrothiazolo[3,4-α]quinoxalin-4-ones

New tricyclic quinoxalinone skeletons with bridge-head nitrogen atoms and containing sulphur in a fully-reduced five-membered ring C were obtained. 3,3a-Dihydrothiazolo[3,4-α]quinoxalin-4-ones I-III were prepared by metal-acid reductive cyclisation of N-(nitrophenyl)- and N-(dinitrophenyl)thiazolidine-4-carboxylic acids IVa,b,c. Attempts to obtain the skeleton by selective hydrogen transfer reductive cyclisation of the corresponding esters Va,b,c were unsuccessful.     

Catalysis of Ugi four component coupling reactions by rare earth metal triflates

Substoichiometric quantities of scandium and ytterbium triflate increase the yield of Ugi four component coupling reactions of aromatic aldehydes 2- to 7-fold. These rare earth metal triflates enhance the reaction yields primarily via activation of the imine intermediate of this multicomponent reaction.     

Directed metalation of pyridinesulphonamides. Synthesis of pyridine-fused isothiazoles and 1,2-oxathioles

4-Lithio-N-t-butylpyridine-3-sulphonamide reacted with benzophenone and carbon dioxide respectively to give the corresponding intermediates which on appropriate treatment gave isothiazolo[5,4-c]pyridin-3-one 1,1-dioxides. Metalation of 2- and 4-(N,N-dialkylaminosulphonyl)pyridines with lithium diisopropylamide (LDA) gave anions which reacted with benzophenone to give carbinols which thermally cyclised to 1,2-oxathiolo[3,4-b]pyridine and 1,2-oxathiolo[4,3-c]pyridine respectively.     

Further investigation into split common fixed point problem for demicontractive operators

Our contribution in this paper is to propose an iterative algorithm which does not require prior knowledge of operator norm and prove strong convergence theorem for approximating a solution of split common fixed point problem of demicontractive mappings in a real Hilbert space. So many authors have used algorithms involving the operator norm for solving split common fixed point problem, but as widely known the computation of these algorithms may be difficult and for this reason, authors have recently started constructing iterative algorithms with a way of selecting the step-sizes such that the implementation of the algorithm does not require the calculation or estimation of the operator norm. We introduce a new algorithm for solving the split common fixed point problem for demicontractive mappings with a way of selecting the step-sizes such that the implementation of the algorithm does not require the calculation or estimation of the operator norm and then prove strong convergence of the sequence in real Hilbert spaces. Finally, we give some applications of our result and numerical example at the end of the paper.     

Environmentally compatible dimethyl sulfoxide: an alternative to N-methylpyrrolidone for electrochemical performance of recycled LiMn1/3Ni1/3Co1/3O2 in lithium-ion battery

The effect of recycling and doping LiMn_1/3Ni_1/3Co_1/3O₂ of lithium-ion battery with dimethyl sulfoxide (DMSO) instead of N-methylpyrrolidone (NMP) on the electrochemical performance of the battery has been investigated for the first time. Observation shows that preparing the cathode active materials with dimethyl sulfoxide will increase the conductivity of the battery. The results show that the as-recovered LiMn_1/3Ni_1/3Co_1/3O₂ modified with LiOH · H₂O calcined at 450°C delivers discharge capacities of about 247 mA h g^?1 in the first cycle with discharge efficiency of 83.1% in sample doped with dimethyl sulfoxide, and 189 mA h g^?1 with discharge efficiency of 82.7% in N-methylpyrrolidone at the rate of 0.2 C. The asrecovered samples calcined at 800 and 850°C deliver 149 and 217 mA h g^?1 in the fourth cycles respectively in dimethyl sulfoxide. The capacity loss observed in dimethyl sulfoxide faded with increase in cycle numbers. In general, for the samples doped with dimethyl sulfoxide, better performances were evident with high discharge capacities in powders calcined at a lower temperature than higher temperature in accordance with particle sizes shown by the SEM images. On the basis of better cyclic performance of lithium metal cathode and environmental safety, it is evident that relatively cheap dimethyl sulfoxide could replace N-methylpyrrolidone in battery formulations. The X-ray diffraction patterns revealed that LiMn_1/3Ni_1/3Co_1/3O₂ was successfully recycled by dimethyl sulfoxide.