For the first time, enantiomerically enriched atropoisomeric furans have been accessed using a central-to-axial chirality conversion strategy. Hence, oxidation of the enantioenriched dihydrofuran precursors gave rise to axially chiral furans with high enantiopurities accounting from excellent conversion percentages (cp) in most cases.
Suitably substituted enantioenriched 4-aryl-1,4-dihydro-pyridines prepared by an organocatalytic enantioselective Michael addition were oxidized with MnO2 into axially chiral 4-arylpyridines with central-to-axial chirality conversion. Moderate to complete percentages (cp) were observed, and a model for the conversion of chirality is discussed.
An atropisomer is a member of a subclass of restricted rotational conformers – this restricted rotation giving rise to stereogenic sigma bonds – that can be isolated as separate chemical species. Most atropisomer are six‐membered‐ring biaryl or heterobiaryl derivatives. The aim of this microreview is to shed light on a less common class of atropisomers, those containing at least one five‐membered hetero‐ or carbocycle and displaying variously a stereogenic C–N, C–C, or even N–N chemical bond. After a short introduction, the occurrence of atropisomers in nature is presented, as well as the synthetic efforts – encompassing non‐stereoselective and diastereoselective strategies, together with an update on very recent enantioselective approaches – devoted to such axially chiral compounds. Finally, a special focus is placed on their important utilization as original and efficient ligands for metal complexes.
Atropisomers possessing multiple stereogenic axes are intriguing molecules with huge potential. However, only few approaches for their enantioselective synthesis are available due to the difficulties in assembling various stereogenic axes with high enantiocontrol. Only recently, innovative methods have emerged, opening new possibilities for the synthesis of this original class of atropisomeric compounds. This Minireview describes the development of this field based on a classification of the multi‐axis systems according to the distance between the stereogenic axes and the strategy used to build them.
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