Bring on the substitute: Even outside of macrocyclic structures, such as vancomycin, appropriate substitution can give rise to atropisomerism in diaryl ethers. Stereochemical stability about the ArOAr axis at room temperature or above is possible when neither of the rings is symmetrically substituted and when at least one ring carries an ortho tert‐butyl group or equivalent.

The orientation of Ar-C, Ar-N and Ar-O bonds in biaryls, N,N'-diarylureas and diaryl ethers (whose conformers are distinguishable by NMR) may be controlled with a selectivity up to >95 : 5 by an adjacent stereogenic centre; the selectivity may be greater when a second stereogenic axis is inserted between the controlling centre and the slowly rotating bond.

Tertiary aromatic amides bearing stereogenic centres ortho to the amide group may adopt two diastereoisomeric conformations which interconvert slowly on the NMR timescale at ambient temperature, and are therefore detectable by NMR. Certain classes of stereogenic centre--particularly sulfoxides, ephedrine-derived oxazolidines, and proline-derived imidazolidines--strongly bias the population of the two conformers. We propose a model, supported by molecular mechanics calculations, which rationalises the sense and magnitude of the conformational selectivity attained in terms of the steric and electronic properties of the controlling centre. The control over conformation may be exploited either by trapping the favoured conformer as an atropisomer, or by using it to relay information about the stereochemistry of the controlling centre.

Modified nucleosides have received a great deal of attention from the scientific community, either for use as therapeutic agents, diagnostic tools, or as molecular probes. Perhaps the most difficult position of a nucleoside to modify is the 4'-position. Chemists have developed innovative methods to achieve this in a stereoselective manner to allow incorporation of a variety of functional groups. This review provides a summary of the most commonly used or recently published methods for ribose, deoxy-ribose, 4'-thioribose, and carbocyclics.

Atropisomeric aromatic amides bearing 2-sulfanyl groups are oxidised by m-CPBA to the corresponding sulfoxides apparently with very high diastereoselectivity. NMR studies and oxidations of chiral benzamides however indicate that the kinetic selectivity of the oxidation is in fact relatively poor, and that the final diastereoisomeric ratio (typically >99:1) is under thermodynamic control, with relatively unhindered Ar-CO rotation readily converting the less stable to the more stable product diastereoisomer. Molecular mechanics indicates that the thermodynamic diastereoselectivity results principally from electrostatic repulsion between the C=O and S-O dipoles.