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Enantiopure (±)-2,6-di-sec-butyl-4-methylpyridine and its oxidized form (±)-2,6-di-sec-butyl-4-methylpyridine-N-oxide were prepared and then separated by chiral HPLC. Their stereochemical structures and their conformational distribution in solution were investigated using vibrational circular dichroism (VCD) and infrared spectroscopy (IR) combined with density functional theory (DFT). The experimental spectra have been compared with theoretical data. This comparison indicated that (−)-2,6-di-sec-butyl-4-methylpyridine and its oxidized form (+)-2,6-di-sec-butyl-4-methylpyridine-N-oxide have an (S,S)-configuration and exist in several conformations. The good fit confirms the reliability of the conformational analysis. Our results indicated that going from the reduced form to the oxidized one strongly influences the type of conformers in solution. Moreover, DFT calculations showed that for all of the conformers of (S,S)-2,6-di-sec-butyl-4-methylpyridine-N-oxide, the formation of four centered intramolecular hydrogen bonds between the hydrogen of the –CH, –CH2, and –CH3 groups and the nitroxide oxygen is possible. Moreover the stability of the conformers of both compounds is influenced by the all-trans structure of the sec-butyl moieties. [ABSTRACT FROM AUTHOR]

Abstract: The enantiomers of 1,3,5-triphenyl-4,5-dihydropyrazole (an intense blue fluorescent compound) have been separated for the first time and their absolute configuration was established by a combination of VCD and ECD measurements and theoretical calculations. The enantiomers of 1,3,5-triphenyl-4,5-dihydropyrazole which are highly fluorescent both in solution (CH2Cl2) and in the solid state may find application in the very active field of enantioselective fluorosensors. [Copyright &y& Elsevier]

Abstract: Pd(II)-coordinated phosphinous acids catalyzed the formal enantioselective [2+1] cycloaddition of norbornene derivatives with terminal alkynes. The absolute configuration of (+)-3aa was assigned using VCD. [Copyright &y& Elsevier]

Graphical abstract Abstract An improved green synthesis of the E2F inhibitor HLM0066474 is described, using solvent-free and microwave irradiation conditions. The two enantiomers are separated using semi-preparative separation on Chiralpak ID and their absolute configuration is determined by vibrational circular dichroism (VCD) analysis. Biological evaluation of both enantiomers on E2F1 transcriptional activity reveals that the (+)- R , but not the (−)- S enantiomer is biologically active in repressing E2F1 transcriptional activity. [ABSTRACT FROM AUTHOR]

The absolute configuration of the resolved axially chiral pyridine- N -oxide derivative, (±)- trans -2,6-di- ortho -tolyl-3,4,5-trimethylpyridine- N -oxide, has been determined by VCD and ECD analyses supported by TD-DFT calculations carried out at different levels of theory. DFT calculations confirmed that in spite of the two biaryl axes, the compound is conformationally less flexible and the major conformer is stabilized by two weak hydrogen bonds formed between the hydrogen of the methyl group of the tolyl moieties and the nitroxide oxygen. The experimental VCD spectra of this compound and the previously studied (±)-2,6-di-sec-butyl-4-methylpyridine-N-oxide with two stereogenic centers were compared in the frequency range 1200–1300 cm −1 . A (+,−,+)/(−,+,−) pattern of bands was observed in both cases. By replacing the sec -butyl moieties with tolyl ones, the VCD peaks shifted toward higher frequencies and the intensities were increased. [ABSTRACT FROM AUTHOR]

Abstract: An inherently chiral ABii diphosphonato cavitand (±)-4 bearing a single quinoxaline bridging moiety was synthesized and resolved by chiral HPLC. Its chiroptical properties were investigated and VCD experiments allowed the determination of its absolute configuration. Distinguishable diastereomeric complexes in solution with l-adrenaline were observed by 1H and 31P NMR together with a noticeable enantio-discrimination at 253K (dr ∼2:1) in favor of the dextrorotatory cavitand (+)-4. [ABSTRACT FROM AUTHOR]