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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 (?G‡ = 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 ?-? interactions in the transition state. Finally, data on a rim-differentiated penta-methyl-penta-propargyl P[5] exhibited the complexity of the overall inversion dynamics.

SUBMITTER: Du K

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

REPOSITORIES: biostudies-literature

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

Du Ke K Demay-Drouhard Paul P Samanta Kushal K Li Shunshun S Thikekar Tushar Ulhas TU Wang Haiying H Guo Minjie M van Lagen Barend B Zuilhof Han H Sue Andrew C-H AC

The Journal of organic chemistry 20200821 17

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 substit ...[more]

PMID: 32820630

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