Diverse Chiral Scaffolds from Diethynylspiranes: All‐Carbon Double Helices and Flexible Shape‐Persistent Macrocycles

Abstract

State-of-the-art chiroptical spectroscopies are valuable tools for structural elucidation. However, the potential of these spectroscopies for everyday applications has not been exploited to date partially due to the lack of sufficiently stable and efficient chiroptical systems. To this end, the development of suitable chiroptical structures is essential. Herein, we present the synthesis of spiro-compounds (P )-1 and (P )-2 as well as (M )-1 and (M )-2 exhibiting remarkable chiroptical responses. Theoretical simulations show that (P )-1, constituted by two (P)-configured spiranic chiral axes, presents an all-carbon double helix structure with (M)-helicity. On the other hand, molecular dynamic simulations reveal (P )-2 to have a single path for geometry-modification along its flat conformational space, certifying it as a chiral flexible shape-persistent macrocycle. Geometric quantification of chirality has been used to compare the spiranic derivatives presented herein.

Spirobifluorene Metallaaromatics

“…[13] The 1 Ha nd 13 C{ 1 H} NMR spectra of 3 show two different signals for the methyl groups in the ortho positions of the mesityl moiety, which indicates hindered rotation about the biaryl bond.E ven when rotation aboutt his bond leads to the same structure, and therefore there is no atropisomerism, the presence of the chiral metal center provides the ortho-methyl groups with diastereotopic character and consequently,t hey are non-equivalent in NMR. Ac omputationals can about the biaryl bond uncovered ar otational barrier of DG ¼ 6 = 40.7 kcal mol À1 .This high energy indicates great stabilityofthe rotamers with interconversion temperature above 473 Ka nd represents ar emarkable t 1/2 increase compared to our previously reported metallaaromaticb iaryl systems, [9] rendering metallaaromatic spirobifluorenes suitable for exploration of axial chirality.Int his regard, we have recently shown theoretically [14] and experimentally [15] the great potential of SBFs for chiroptical applications.…”

“…This red shift is among the strongestr eported for monosubstituted SBFs pointing out the strong influence of the iridium atom (Figure 4, for more details see the SI). [1] On the other hand, time-dependent density functional theory (TD-DFT) studies of an iridanabencenea naloguei ndicate that the incorporation of the SBF fragment is (15);Ir ÀC11: 1.962(5);C11ÀC12:1.415(7);C 12ÀC13: 1.367(7);C13ÀC32:1.452(6); C32ÀC33:1.433(7); IrÀC33:2.057(5);C32ÀC31: 1.432(7);C31ÀC30:1.373(7); C30ÀC35:1.414(7);C35ÀC34: 1.387(7);C 34À C33:1.401(7). also havingastrong influence (for more information see the SI).…”

Design and synthesis of chiral spirobifluorenes

“…Purification via flash column chromatography (SiO 2 , gradient from 25% to 30% EtOAc/ n ‐hexane) gave ( ± ) ‐3 as pale yellow solid (155.0 mg, 78%). Spectroscopic data matched to that of previously reported . 1 H NMR (400.16 MHz, CDCl 3 , δ ): 7.9 – 7.8 (m, 4H), 7.53 (dd, J = 7.9, 1.4 Hz, 1H), 7.45 (dd, J = 7.9, 1.4 Hz, 1 H), 7.39 (td, J = 7.5, 1.0 Hz, 1H), 7.38 (td, J = 7.5, 1.0 Hz, 1H), 7.14 (td, J = 7.5, 1.0 Hz, 1H), 7.13 (td, J = 7.5, 1.1 Hz, 1H), 6.84 (dd, J = 1.3, 0.5, 1H), 6.77 (dd, J = 1.4, 0.5, 1H), 6.73 (d, J = 7.6 Hz, 1H), 6.72 (d, J = 7.6 Hz, 1H), 2.97 (s, 1H, C≡C─H), 1.52 (s, 6H, 2×CH 3 ) ppm.…”

“…In comparison with different positional isomers, 2‐substituted SBFs are particularly available for the extension of conjugation, leading to tuning optical properties in a well‐controlled fashion . Seeking for a more robust chiral axis, we have theoretically and experimentally evaluated the reliability of SBFs in the construction of stable systems presenting remarkable chiroptical responses in solution. Consequently, we herein report the design, synthesis, and AC assignment of thioacetate functionalized SBFs CF ‐ 3 , CF ‐ 4 , and CF ‐ 5 as a milestone towards the development of chiroptical surfaces (Scheme ).…”

Chiroptical Symmetry Analysis (CSA): on the Way from the Understanding of Highly Symmetric Systems to the Development of Chiroptical Applications

“…This outcome is comparable with the analysis of a C2 and D2 symmetric systems in terms of the selection rules. In recent year a number of highly symmetric systems such as linear [5] and cyclic oligomers [10], molecular containers [11,12] or even all-carbon double helices [13] presenting remarkable chiroptical responses have been developed on the search for valuable materials for everyday chiroptical applications [14]. However, analysis of the chiroptical responses is often tedious [15,16].…”