Chromane helicity rule--scope and challenges based on an ECD study of various trolox derivatives.

The validity of the chromane helicity rule correlating the sense of twist within the dihydropyran ring with the CD sign of the (1)Lb band observed at ca. 290 nm in their electronic circular dichroism (ECD) spectra is examined using a set of natural (S)-trolox derivatives. To investigate both the scope and the limitations of the rule a combination of ECD spectroscopy, especially the temperature dependence of the ECD spectra, single crystal X-ray diffraction analyses, and density functional theory (DFT) calculations was used.

Dimolybdenum tetracarboxylates as auxiliary chromophores in chiroptical studies of vic-diols.

The aim of the present work was to check the suitability of dimolybdenum carboxylates, other than commonly used [Mo2(OAc)4], as auxiliary chromophores for determining the absolute configuration of optically active vic-diols by means of electronic circular dichroism (ECD). To this end, a set of dimolybdenum tetracarboxylates was synthesized, and subsequently, the two most promising compounds were selected, namely dimolybdenum tetrakis(μ-pivalate) and tetrakis(μ-isovalerate). The selection was based on their solubility in commonly used solvents, their stability in solution, their tolerance to air exposure, as well as their utility for dichroic studies.

Distinguishing between polymorphic forms of linezolid by solid-phase electronic and vibrational circular dichroism.

For the first time two crystalline forms of the same compound (linezolid polymorphs) were investigated by means of the solid-phase ECD and VCD spectra. The ECD spectra show distinct differences and the band at 221 nm serves as a diagnostic one because it is present in form II but absent in form III. The VCD spectra strongly differ in the diagnostic carbonyl absorption range exhibiting two relatively strong bands of opposite signs.

Practical method for the absolute configuration assignment of tert/tert 1,2-diols using their complexes with Mo2(OAc)4.

We describe here an application of the practical, simple, and reliable approach for the determination of the absolute configuration of sterically demanding tert/tert vic-diols. According to this method, it is only necessary to mix dimolybdenum tetraacteate and a chiral diol in DMSO and record the CD spectra in the 250-650 nm spectral range. From the sign of the CD bands occurring at around 310, 350, and 400 nm, it is possible to establish the chirality of the diol unit expressed by the sign of the O-C-C-O torsion angle.

Chiral ytterbium complex-catalyzed direct asymmetric aldol-Tishchenko reaction: synthesis of anti-1,3-diols.

The asymmetric aldol-Tishchenko reaction of aromatic aldehydes with aliphatic and aromatic ketones has been developed as an efficient strategy for the synthesis of anti-1,3-diols in good yield with high diastereocontrol and good levels of enantioselectivity. This domino-type reaction is catalyzed by a chiral ytterbium complex that promotes both the aldol reaction through enolization of the carbonyl compound and the Evans-Tishchenko reduction of the aldol intermediate. The stereochemistry of the resulting diols is also investigated and finally proved by using CD techniques.