Magdalena Jawiczuk

Amine-Catalyzed Direct Aldol Reactions of Hydroxy- and Dihydroxyacetone: Biomimetic Synthesis of Carbohydrates

This article presents comprehensive studies on the application of primary, secondary, and tertiary amines as efficient organocatalysts for the de novo synthesis of ketoses and deoxyketoses. Mimicking the actions of aldolase enzymes, the synthesis of selected carbohydrates was accomplished in aqueous media by using proline- and serine-based organocatalysts. The presented methodology also provides direct access to unnatural L-carbohydrates from the (S)-glyceraldehyde precursor. Determination of the absolute configuration of all obtained sugars was feasible using a methodology consisting of concerted ECD and VCD spectroscopy.

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. The stability of the obtained in situ chiral complexes was verified by measuring the dependence of ECD, UV-vis, and NMR spectra on time, temperature, and concentration. We have shown that the ECD spectra of diverse vic-diols with these complexes are suitable for configurational assignment based on the correlation between signs of Cotton effects (CEs) arising in the spectra and the stereostructure of the ligand. Furthermore, to aid in the interpretation of experimental results, a separate set of DFT calculations has been incorporated to provide additional insight into the structure of the chiral complexes involved. In contrast to the earlier assumptions, experiments showed that the chelating mode of ligation is preferred for the studied complexes.

Synthesis of a sucrose dimer with enone tether; a study on its functionalization.

Summary The reaction of appropriately functionalized sucrose phosphonate with sucrose aldehyde afforded a dimer composed of two sucrose units connected via their C6-positions (‘the glucose ends’). The carbonyl group in this product (enone) was stereoselectively reduced with zinc borohydride and the double bond (after protection of the allylic alcohol formed after reduction) was oxidized with osmium tetroxide to a diol. Absolute configurations of the allylic alcohol as well as the diol were determined by circular dichroism (CD) spectroscopy using the in situ dimolybdenum methodology.

The utility of dimolybdenum tetrakis (μ-isovalerate) and tetrakis (μ-pivalate) in the stereochemical studies of various transparent compounds

The aim of the present work was to verify the usefulness of dimolybdenum tetrakis(μ-pivalate) and tetrakis(μ-isovalerate) as auxiliary chromophores for determining the absolute configuration of optically active vic-diamines, vic-amino alcohols, α-amino and α-hydroxy acids by means of electronic circular dichroism (ECD). To this end, a series of measurements designed to check the dependence of ECD and UV-Vis spectra on time and concentration was carried out. The experimental results were supported by a separate set of detailed DFT calculations. The results obtained allowed us to determine the most probable structure of dominating chiral complexes formed in situ in solution for all ligands studied.