Correlating Solution‐ and Solid‐State Structures of Conformationally Flexible Resorcinarenes: Significance of a Sulfonyl Group in Intramolecular Self‐Inclusion

Abstract

The synthesis of tetramethoxyresorcinarene podands bearing p‐toluene arms connected by ‐SO3‐ (1) and ‐CH2O‐ (2) linkers is presented herein. In the solid state, the resorcinarene podand 1 forms an intramolecular self‐inclusion complex with the pendant p‐toluene group of a podand arm, whereas the resorcinarene podand 2 does not show self‐inclusion. The conformations of the flexible resorcinarene podands in solution were investigated by variable‐temperature experiments using 1D and 2D NMR spectroscopic techniques as well as by computational methods, including a conformational search and subsequent DFT optimisation of representative structures. The 1H NMR spectra of 1 and 2 at room temperature show a single set of proton signals that are in agreement with C4v symmetry. At low temperatures, the molecules exist as a mixture of boat conformations featuring slow exchange on the NMR timescale. Energy barriers (ΔG≠298) of 55.5 and 52.0 kJ mol−1 were calculated for the boat‐to‐boat exchange of 1 and 2, respectively. The results of the ROESY experiments performed at 193 K and computational modelling suggest that in solution the resorcinarene podand 1 adopts a similar conformation to that present in its crystal structure, whereas podand 2 populates a more versatile range of conformations in solution.

Novel octacationic-resorcin[4]arenes featuring quaternary ammonium groups as multivalent biocides

“…In particular, one aryl ring of ResQAC butyl is slightly inward oriented, and the other is slightly outward oriented (Figures 3c,d), defining two almost parallel inclined sides of the boat (3.8°). This observation of a more open conformation of ResQAC butyl than other resorcinarenes in boat conformation 26,27 is consistent with the presence of the electrostatic repulsion between positively charged quaternary alkylammonium side chains. Close inspection of the 1 H NMR spectrum of ResQAC butyl in CD 3 CN (Figure 4a, 400 MHz, 298 K) clearly indicated that the macrocycle adopts, also in solution, a C 2v −boat conformation, stable in the NMR time scale at 298 K (400 MHz).…”

Menthyl esterification allows chiral resolution for the synthesis of artificial glutamate analogs

“…With 10* (2S) in hand, (2S)-MC-27 (4*) was synthesized in a reasonable yield (62%) by acidic hydrolysis (Scheme 4). The chromatographic behavior and the spectroscopic data ( 1 H and 13 C NMR) of (2S)-MC-27 (4*) thus synthesized were identical to those of the antipode 4 (see above as well as Scheme 3 and Scheme 4).…”

“…These take a stable extended conformation in the calculations and in the NMR experiment, whereas a rather folded conformation is taken in the crystals. Such a discrepancy is often observed and reported in small molecules and biomacromolecule due to intermolecular or intramolecular H-bonds and/or hydrophobic interactions [ 13 ].…”

Enaminone Substituted Resorcin[4]arene—Sealing of an Upper-Rim with a Directional System of Hydrogen-Bonds

“…Currently, several types of inherently chiral derivatives of resorcin[4]arenes are known in the literature. They involve derivatives that are covalently linked by modifications of hydroxyl groups [ 12 , 13 , 14 ] or by simultaneous modifications of the “ortho” position of the resorcin[4]arene and hydroxyl groups (via the Mannich reaction [ 15 ], cycloaddition reaction of o-quinomethide derivative of resorcin[4]arene with dienophiles [ 16 , 17 ], bridging with boron [ 18 ] or formation coumarin–type rings [ 19 ]. It has also been shown that inherent chirality can be induced in the non-covalent way by a system of hydrogen bonds and the barrier of racemization is relatively high (halflives the range of seconds to minutes) [ 20 , 21 ].…”