Formation of a stable 14-helix in short oligomers of furanoid cis-beta-sugar-amino acid

Oligomers of a new class of sugar amino acids (SAA) using a xylofuranoic acid has been shown to generate a robust 14-helix. The design involved the use of xylofuranose with a cis arrangement between the amine and carboxyl groups to promote the adoption of a 14-helix instead of a mixed 12/10-helix observed in a sugar oligomer using a ribofuranoic acid and beta-Ala. The observation of a stable right-handed 14-helix in a cis-SAA is unprecedented.     

Gem‐disubstituted 4‐oxocyclohexanes: Source for spiro heterocycles

Novel spiro heterocycles, substituted spiro‐pyrimidine, pyrazole and isoxazole compounds are prepared by the cyclocondensation of 4‐oxocyclohexane gem‐dicarboxylates and cyano esters with nucleophiles.     

Ortho effects in organic molecules on electron impact. Part 15. Oxygen transfers from the nitro group to both sulphur and olefinic double bonds in allyl o-nitrophenyl sulphide

An oxygen transfer from the nitro group to the C?C group, followed by a simple cleavage, afford intense fragments corresponding to o-nitrosothiophenol at m/z 139 and o-nitrosothiophenoxy cation at m/z 138 during mass spectral fragmentations of allyl o-nitrophenyl sulphide. Further, a concerted double oxygen transfer from the nitro group to the sulphur is proposed for the ejection of ?O₂H from the molecular ion of this compound, leading to the quinolinium cation at m/z 130. These processes are supported by the high-resolution data, collision-induced dissociation linked-scan spectra and chemical evidence.     

Unexpected mass spectral skeletal rearrangements in aromatic thioamides

Interesting skeletal rearrangements, resulting in the formation of unexpected fragments, have been noticed in the mass spectra of aromatic thioamides of cyclic amines such as piperidine, morpholine and pyrrolidine. Suitable mechanisms, based on mass analysed ion kinetic energy spectra, high voltage scan spectra and high resolution data, have been proposed for the formation of [M? SH]⁺ ions and the fragment at m/z (103+R) in the mass spectra of these compounds. The mass spectra of the thioamides of non-cyclic amines and the thioamides of aliphatic acids contain peaks corresponding to a four-centred skeletal rearrangement followed by the elimination of either the thioalkoxy or the thiophenoxy radical from the molecular ions.     

Some studies on thallium oxalates — IV

Thallium(III) was precipitated with oxalic acid in the presence of 0.025M RbNO₃ (or 0.0125M Rb₂SO₄) in 0.1M HNO₃ (or 0.05M H₂SO₄). Chemical analysis of the solid obtained corresponds to the formula Rb[Tl^III(C₂O₄)₂]·4 H₂O. Thermal studies (TG, DTG and DTA) indicated the dehydration and redox decomposition of the thallic salt to the thallous salt, and finally to a mixture of rubidium carbonate and oxides of thallium(I) and thallium(III). Infrared absorption spectra, microscopic observations and X-ray diffraction data were used to characterize the original salt, as well as the intermediates formed during the thermal decomposition of the salt. On the basis of these results, the salt may be represented as: Rb[Tl^III(C₂O₄)₂(H₂O)₂]·2 H₂O.

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Zusammenfassung Thallium (III) wurde mit Oxalsäure in Gegenwart von 0.025M RbNO₃ (oder 0.0125M Rb₂SO₄) in 0.1M HNO₃ (oder 0.05M H₂SO₄) gefällt. Die chemische Analyse der erhaltenen Festsubstanz entspricht der Formel Rb[Tl^III(C₂O₄)₂]·4H₂O. Thermische Untersuchungen (TG, DTG und DTA) zeigen die Dehydratisierung und Redoxzersetzung vom Thallitsalz zum Thallitsalz und schließlich zu einem Gemisch von Rubidiumcarbonat und Oxiden der Thallium(I) und Thallium(III). Infrarot-Absorptionsspektren, mikroskopische Beobachtungen und Röntgendiffraktionsdaten werden zur Charakterisierung des ursprünglichen Salzes sowie der während der thermischen Zersetzung des Salzes entstandenen Zwischenprodukte angewandt. Durch diese Ergebnisse kann das Salz wie folgt beschrieben werden: Rb[Tl^III(C₂O₄)₂(H₂O)₂]·2H₂O.

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() 0.025M RbNO₃ ( 0.0125M Rb₂SO₄) 0.1M HNO₃ ( 0.05M H₂SO₄) , Rb[Tl¹¹¹(C₂O₄)₂]. 4₂. (, ) - (). , , , . , Rb[Tl¹¹¹(C₂O₄)₂(H₂O)₂·2₂O.

     

Synthetic studies toward tricyclic cembranoids: a modular approach for the construction of the tricyclic framework of eunicin

The synthesis of a sugar derived allene and its intramolecular silver mediated etherification followed by ring closing metathesis has been explored for building the tricyclic framework of eunicin.     

Dichromate titration of thallium(I)

The formal redox potentials of the thallium(III)-thallium(I) couple in different acids of varying strengths are reported. The minimum concentration of hydrochloric acid required for a direct titration of thallium(I) with potassium dichromate is 5M. Thallium(I) can be titrated directly with the primary standard oxidant, potassium dichromate, at room temperature, with ferroin as indicator, in 6M hydrochloric acid. Atmospheric oxygen must be excluded.     

A new and convenient synthesis of 13,16-diazaestrone analogs

Imidazolidine-2,4-dione was chemoselectively N-alkylated at the imidic NH with several 2-(3,4-dihydro-1-naphthalenyl)ethyl-4-methylphenylsulphonates to give the corresponding imides for the first time which on selective reduction at one of the carbonyl groups followed by cyclization in PPA gave the corresponding title compounds.     

CNDO calculations of N-methyl substituted acrylamides

CNDO calculation is made for N-methyl acrylamide (both incis andtrans configurations) and N,N-dimethyl acrylamide. The charges, bond orders and dipole moments are discussed and compared with those of acrylamide. Thetrans form of N-methyl acrylamide is found to be more stable thancis isomer by 4.5 kcal/mole.     

DBU Acetate Mediated: One‐pot Multi Component Syntheses of Dihydropyrano[3,2‐c]quinolones

Three‐component reaction involving condensation of 1‐methylquinoline‐2,4(1H,3H)‐dione( 1 ), aromatic aldehydes ( 2a , 2b , 2c , 2d , 2e , 2f , 2g , 2h ) and malononitrile/cyanoaceticester ( 3a , 3b ) in{(1,8‐diazabicyclo[5.4.0]‐undec‐7‐en‐8‐ium acetate)}[DBU][Ac] as task‐specific ionic liquid leading to the efficient synthesis of dihydropyrano[3,2‐c]quinolones ( 4a , 4b , 4c , 4d , 4e , 4f , 4g , 4h , 4i , 4j , 4k , 4l , 4m , 4n , 4o , 4p ) is described. This approach is convenient, mild, and affords the products in high yields without the use of column chromatography.