Stereochemical Inversion of Rim-Differentiated Pillar[5]arene Molecular Swings.

ABSTRACT: To investigate the dynamic stereochemical inversion behavior of pillar[5]arenes (P[5]s) in more detail, we synthesized a series of novel rim-differentiated P[5]s with various substituents and examined their rapid rotations by variable-temperature NMR (203-298 K). These studies revealed for the first time the barrier of "methyl-through-the-annulus" rotation (ΔG^‡ = 47.4 kJ·mol^-1 in acetone) and indicated that for rim-differentiated P[5]s with two types of alkyl substituents, the smaller rim typically determines the rate of rotation. However, substituents with terminal C═C or C≡C bonds give rise to lower inversion barriers, presumably as a result of attractive π-π interactions in the transition state. Finally, data on a rim-differentiated penta-methyl-penta-propar

SUBMITTER: Du K 

PROVIDER: S-EPMC7498154 | biostudies-literature | 2020 Sep

REPOSITORIES: biostudies-literature