Increasing chiral recognition in acetal formation

Abstract

The design of substituted lactols is described, which in their reaction with racemic alkyl aryl carbinols react preferentially with one of the enantiomers exhibiting selectivities up to 14:1.

Chiral resolution of alcohols by extractive separation of acetals

“…A prerequisite for the applicability of this method of extractive racemate resolution is high enantiomer selectivity in acetal formation [4,6]. At the same time, facile preparation of the compounds, required hydrophilic-lipophilic solubility properties of the diastereomers, and easy handling during extraction were also considered to be important criteria.…”

“…1) under thermodynamic conditions with an excess of racemic alkylarylcarbinol leads to a preferred BB structure in comparison to the BA compound [3]. In order to provide an understanding of this preferred formation of the structure, we will first discuss the stereoelectronic effects [4]. By analyzing the steric effects we find a preferred antiperiplanar arrangement of the C(3)-C (2) bond and the C*-b bond in the BB, as in the BA structure.…”

“…In this case the isolation is easy and usually occurs with high yield. However, if the obtained diastereoisomer does not crystallize, excess alcohol enriched with the unreacted enantiomer has to be removed, preferably by flash chromatography [4,7]. In order to develop a more straightforward modification of this process, we chose to synthesize lactols with an acidic side chain, which can be separated from the excess of carbinol by extraction of their salt.…”

Chirality Transfer in the Formation of Poly(oxymethylene) Helices by Anionic Polymerization

“…50 -758). 13 C-NMR (CDCl 3 ): 143.0 (s, arom C(1)); 128.4 (d, C(3) and C(5)); 127.5 (d, C(4)); 126.2 (d, arom. (400 ml of 10% aq.…”

“…By applying the b, pl, H-rule [12] [13], a right handed helix is observed when the starting and the end group has an A descriptor [14], whereas a left-handed helix is obtained with a B descriptor as start and end group, respectively. Poly(oxymethylene) serves as the most general model of the anomeric effect, namely the interaction of the n o lone pair of the O-atom and the s* orbital of the CÀO bond [15].…”