Dielectric anomaly at T_N in LaMnO3

We observe a distinct anomaly in dielectric permittivity (epsilon') as well as relaxation time (tao_0) versus temperature (T) pattern at the antiferromagnetic transition point (T_N) in single crystal of LaMnO3. The equivalent circuit analysis of the impedance spectra across T_N reveals clear anomaly in the capacitive component C_0 at T_N. Since no structural transition takes place across T_N, the anomaly in tao_0 and C_0 at T_N possibly signifies multiferroicity stemming from coupling between orbital and spin order in LaMnO3.Comment: 14 pages including 3 figures; pdf only; accepted for publication in Phys. Rev.

Asymmetric synthesis. Part 5. Asymmetric reduction of phenyl trifluoromethyl ketone with chiral alkoxy-aluminium and -magnesium halides

Phenyl trifluoromethyl ketone has been asymmetrically reduced with a number of chiral alkoxy-aluminium and -magnesium halides derived from bornan-2-exo- and -endo-ols, p-menthan-3-ol, and 1-phenylethanol. Bornan-2-endo-yloxyaluminium dichloride and p-menthan-3-yloxyaluminium dichloride are highly stereoselective and reduce the ketone to give 2,2,2-trifluoro-1 -phenylethanol with 68 and 77% enantiomeric excess, respectively. The results are discussed in terms of appropriate transition states

New Chiral Borohydride Based Reducing Agent : Asymmetric Reduction of 9-Anthryl Trifluoromethyl Ketone and Other Carbonyl Compounds

(S)-(+)-2-(a-Hydroxybenzyl)benzimidazole (1) and (S)-(-)-2- benzimidazole-1 -ethanol (2) were synthesised and converted to chiral borohydrides which reduced prochiral ketones to the corresponding chiral alcohols in high yields (80 to loo%, e.e. 42 to 95%). This is the first report of sodium borohydride modified by 1,2-amino alcohol

Stereoselective Synthesis of Chiral Oxepanes and Pyrans through Intramolecular Nitrone Cycloaddition in Organized Aqueous Media

A highly stereoselective surfactant-catalyzed intramolecular nitrone (formed by dehydration in water) cycloaddition in aqueous media leading to exclusive formation of a single isomer is reported. Either oxepane or pyran is formed from 3-O-allyl furanoside derivatives, which constitute the framework of a large number of biologically active compounds. Therefore, the environmentally friendly, efficient, and highly stereoselective syntheses of these chiral intermediates are still a meaningful pursuit

Polycyclic systems. Part 17. Proton nuclear magnetic resonance spectra of some 11H-lndeno[2,1-a]phenanthrene derivatives; structure of the C<SUB>26</SUB> hydrocarbon (second diels hydrocarbon) from cholesterol

The n.m.r. spectra of a number of 11H-indeno[2,1-a]phenanthrenes, including the C26 hydrocarbon (second Diels hydrocarbon) from cholesterol, and their 11-oxo-derivatives have been studied. These data together with some previous observations identify the hydrocarbon as 8-isobutyl-10-methyl-11H-indeno[2,1-a]phenanthrene (21), its formation being rationalised in terms of 1,2-shift of the side chain in ring D, followed by a similar shift of the 13-methyl group and its final inclusion in ring E of the indenophenanthrene (21)

Dehydrative Intramolecular Nitrone Cycloaddition in Confined Aqueous Media: a Green Chemical Route to Cis-Fused Chromano[4,3-c]Isoxazoles

An efficient synthetic route to the formation of cis-fused chromano[4,3-c]isoxazoles via dehydrative intramolecular 1,3-dipolar nitrone cycloaddition in organized aqueous media in the presence of a surfactant (viz. CTAB) as catalyst was developed, which indeed appeared to be green and a more sustainable method than the existing methods with the additional advantage of easy isolation of products

A green chemical approach for the N-alkylation of aldoximes to form nitrones in organized aqueous media and their in situ cycloaddition with olefins

Aldoximes react with a,b-unsaturated carbonyl and sulfonyl compounds in organized aqueous media (nanoreactor system) using dodecylbenzenesulfonic acid (DBSA) as surfactant to generate N-alkylated nitrones, which undergo intermolecular cycloaddition in the same pot with maleimides to give the desired cycloadduct in absence of any organic solvent and catalyst. Divinyl sulfone was successfully used for both N-alkylation and intramolecular cycloaddition, affording only one cycloadduct. This is a new example of green chemistry and provides a new aspect of reactions in water