The reported enantioselective synthesis for the preparation of (+)-(2R,3R)-2-(4-
hydroxy-3-methoxyphenyl)-3-hydroxymethyl-1,4-benzodioxane-6-carbaldehyde, precursor
for the stereoselective synthesis of bioactive flavanolignans, could not be reproduced.
Thus, the target molecule was prepared via the synthesis and separation of diastereomeric
O-glucosides. TDDFT-ECD calculations and the 1,4-benzodioxane helicity rule were utilized
to determine the absolute configuration. ECD calculations also confirmed that the 1Lb
Cotton effect is governed by the helicity of the heteroring, while the higher-energy ECD
transitions reflect mainly the orientation of the equatorial C-2 aryl group.
The widespread occurrence and significance of chiral compounds does not only require new methods for their enantioselective synthesis but also efficient tools that allow rapid determination of the absolute configuration,...
Abstract The first enantioselective synthesis of a photoreactive (R)-β-phenylalanine is described. In the key step, m-diazirinyl-substituted benzaldehyde is converted to a chiral sulfinimine in a Ti(OEt)4- mediated reaction, followed by diastereoselective enolate addition. The absolute configuration of photo (R)-β-phenylalanine was confirmed by Mosher analysis. The photo amino acid proved to be thermally stable under standard laboratory conditions. Irradiation in toluene afforded cycloheptatriene=norcaradiene valence tautomers, together with carbene benzylation. Quantumchemical calculations indicate a small triplet-singlet gap.
Rapid Organocatalytic Chirality Analysis of Amines, Amino Acids, Alcohols, Amino Alcohols and Diols with Achiral Iso(thio)cyanate Probes
