Syntheses and Properties of Enantiomerically Pure Higher (n ≥ 7) [n−2]Triangulanedimethanols and σ-[n]Helicenes.

de Meijere, A.; Khlebnikov, A.F.; Kozhushkov, S.I.; Yufit, D.S.; Chetina, O.V.; Howard, J.A.K.; Kurahashi, T.; Miyazawa., K.; Frank, D.; Schreiner, P.R.; Rinderspacher, B.C.; Fujisawa, M.; Yamamoto, C.; Okamoto, Y.

Abstract

(P)-(+)-Hexaspiro[2.0.0.0. 0.0.2.1.1.1.1.1]pentadecane [(P)-17] as well as (M)-(−)- and (P)-(+)-octaspiro[2.0.0.0.0.0.0.0.2.1.1.1.1.1.1.1]nonadecanes [(M)- and (P)-25]—enantiomerically pure unbranched [7]- and [9]triangulanes—have been prepared starting from racemic THP-protected (methylenecyclopropyl)methanol 6. The relative configurations of all important intermediates as well as the absolute configurations of the key intermediates were established by X-ray crystal structure analyses. This new convergent approach to enantiomerically pure linear [n]triangulanes for n=7, 9 was also tested in two variants towards [15]triangulane. Some of the most prominent and unexpected features of the newly prepared compounds are the remarkable modes of self-assembly of the diols (P)-14, (E)-(3S,3′S,4S,4′S,5R,5′R)-21, (P)-(+)-22, and (E)-31 in the solid state through frameworks of intermolecular hydrogen bonds leading to, depending on the respective structure, nanotube- [(P)-14, (P)-(+)-22, and (E)-31], honeycomb-like structures [(E)-(3S,3′S,4S,4′S,5R,5′R)-21] or a supramolecular double helix [(P)-(+)- and (M)-(−)-22]. Liquid crystalline properties of the esters and ethers of the diols (P)-14, (P)-, and (M)-22 have also been tested. Although all of these [n]triangulanes have no chromophore which would lead to significant absorptions above 200 nm, they exhibit surprisingly high specific rotations even at 589 nm with [α]equation image=+672.9 (c=0.814 in CHCl3) for (P)-(+)-17, +909.9 (c=0.96 in CHCl3) for (P)-(+)-25, −890.5 (c=1.01 in CHCl3) for (M)-(−)-25, and −1302.5 (c=0.36 in CHCl3) for (M)-(−)-39, and the specific rotations increase drastically on going to shorter wavelengths. This outstanding rotatory power is in line with their rather rigid helical arrangement of σ bonds, and accordingly these helically shaped unbranched [n]triangulanes may be termed “σ-[n]helicenes”, as they represent the σ-bond analogues of the aromatic π-[n]helicenes. Density functional theory (DFT) computations at the B3 LYP/6-31+G(d,p) level of theory for the geometry optimization and time-dependent DFT for determining optical rotations with a triplet-ζ basis set (B3 LYP/TZVP) reproduce the optical rotatory dispersions (ORD) very well for the lower members (n=4, 5) of the σ-[n]helicenes. For the higher ones (n=7, 9, 15) the computed specific rotations turn out increasingly larger than the experimental values. The remarkable increase of the specific rotation with an increasing number of three-membered rings is proportional neither to the molecular weight nor to the number of cyclopropane rings in these σ-[n]helicenes.

Citation

de Meijere, A., Khlebnikov, A., Kozhushkov, S., Yufit, D., Chetina, O., Howard, J., …Okamoto, Y. (2006). Syntheses and Properties of Enantiomerically Pure Higher (n ≥ 7) [n−2]Triangulanedimethanols and σ-[n]Helicenes. Chemistry - A European Journal, 12(22), 5697-5721. https://doi.org/10.1002/chem.200600111

• Journal Article Type: Article
• Publication Date: 2006-07
• Journal: Chemistry - A European Journal
• Print ISSN: 0947-6539
• Publisher: Wiley
• Peer Reviewed: Peer Reviewed
• Volume: 12
• Issue: 22
• Pages: 5697-5721
• DOI: https://doi.org/10.1002/chem.200600111
• Keywords: Chirality, Helical structures, Optical rotations, Self-assembly, Small ring systems.
• Public URL: https://durham-repository.worktribe.com/output/1543824