Nuclear magnetic resonance elucidation of ring-inversion processes in macrocyclic octaols

Abstract

The conformational behaviour of the three macrocyclic octaols (4)-( 6), obtained b y acid-catalysed condensation of resorcinol with heptanal, is elucidated for the first time. T w o of them, namely the diamond (5a) and the chair (6a) stereoisomers, undergo a ring-inversion conformational process in acetone to give the corresponding crown conformers (5b) and (6b). In DMSO or on addition of acetic acid to an acetone solution of diamond octaol ( 5 ) , conformer (5a) is favoured. The presence of such equilibria and solvent effects are interpreted as an interplay between the tendency of the phenolic OH groups to form intramolecular hydrogen bonds and the alkyl chains to assume the endo position, avoiding steric repulsions and allowing self-aggregation.

A supported liquid membrane (SLM) with resorcinarene for facilitated transport of methyl glycopyranosides: Parameters and mechanism relating to the transport

“…A special attention was given to the synthesis of carrier 1, because this macrocycle is known to possess several diastereoisomeric forms [27,28]. We ensured the exclusive formation of the thermodynamically more stable crown form by heating the crude condensation mixture at reflux for at least 4 h [27].…”

Synthesis and properties of potassium salts of per-O-carboxymethyl-calix[4]pyrogallols and their complexes with Cu2+, Fe3+, and La3+

“…32 These isomers are charac terized by the predomination of the averaged С 4v sym metry, which is a result of fast equilibration between two equivalent boat conformations with transition through the cone conformation with the symmetry С 4v . 33 The study of calix [4]resorcinols unsubstituted and functionalized at the hydroxy groups of calix [4]resorcinols showed that the rccc isomer does not transform into other isomers even at high temperatures. 33, 34 Other, predominantly rctt isomers are usually formed during the condensation of resorcinols and pyrogallols with more bulky aromatic aldehydes.…”

A new, conformationally mobile macrocyclic core for bowl-shaped columnar liquid crystals

“…The high conformational mobility of l a was demonstrated by deuterium NMR measurements: the macrocyclic ring inversion process was frozen only at -90°C in acetone-d,, with l a locked in the crown conformation [12,13]. The conformational mobility of the core in derivatives lb-i is only slightly decreased by the presence of twelve bulky acyl groups (lb mobility was frozen out at -70°C in acetone-d,).…”