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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 (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-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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