Conformational preferences in diastereomeric(5S)‐methyl‐3‐(o‐aryl)‐2,4‐oxazolidinediones

Abstract

The thermally interconvertible diastereomers of the (5S)-methyl-3-(o-aryl)-2,4-oxazolidinediones were synthesized and their conformers studied by (1)H NMR and HPLC. The barriers to rotation about the N-C(aryl) bond were found to be very much solvent dependent. For the o-fluoro oxazolidinedione, difference in barriers to rotation in deuterated methanol and deuterated chloroform amounted to 34 kJ/mol. ortho-Bromo substitution increased the barrier to rotation up to 100 kJ/mol in ethanol, which enabled the analytical separation of the diastereomers and observation of the thermodynamic enrichment of the S-P conformer by HPLC. In CDCl(3) by (1)H NMR, on the other hand, a barrier of only 89 kJ/mol was determined. The S-M and S-P conformers of the diastereomers of o-methyl, alpha-naphthyl and o-iodo derivatives have been assigned by NOESY experiments and the kinetic and thermodynamic constants for the interconversion between the S-M and S-P conformers were determined.

Synthesis of bis[N-(p-aryl)-carbamoyloxy]alkanes as new low-molecular weight organogelators

“…Design and the synthesis of the bis-carbamate compounds 36,64,65 Bis[N-(p-aryl)-carbamoyloxy]alkanes were first synthesized (except 3-Naph, 66 4-Naph, 67e69 (4-6)-Me, 70e72 and (4-6)-OMe 70e72 ) by the reaction of diols (1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol) and p-aryl isocyanates in toluene (Scheme 2). The investigated bis-carbamate molecules consist of three different structural units, shown in Scheme 1: (1) a carbamate unit, that is, capable of forming hydrogen bonds, (2) an aryl moiety substituted by electron donating groups, which might increase the strength of pep stacking, and (3) aliphatic spacers of different length (n¼3e6) that can be involved in van der Waals interactions.…”

“…p-Aryl isocyanates were prepared according to already described procedure 64,65 and identified by their IR spectra (2259e2275 cm À1 ).…”

Axially chiral N‐(o‐aryl)‐4‐hydroxy‐2‐oxazolidinone derivatives from diastereoselective reduction of N‐(o‐aryl)‐2,4‐oxazolidinediones: Thermally interconvertible atropisomers via ring‐chain‐ring tautomerization

“…1). The barriers to enantiomerization of the N-(o-aryl)-4-hydroxy-5,5-dimethyl-2-oxazolidinone enantiomers have been determined by either enantioselective HPLC by following the interconversion of one resolved enantiomer peak to the other or by temperature dependent 1 H NMR.…”

Axially chiral N-(o-aryl)-2-thioxo-oxazolidine-4-one and rhodanine derivatives: enantiomeric separation and determination of racemization barriers

“…Based on our experiences with thermally interconvertible, axially chiral compounds, [11][12][13][14][15][16][17][18][19] the synthesis of N-ortho-aryl-substituted heterocyclic compounds, as shown in Scheme 1, has been planned.…”