Inherently Chiral Iminoresorcinarenes through Regioselective Unidirectional Tautomerization

Abstract

Tetraformylresorcin[4]arene is obtained in 48% yield via a chromatography-free Duff reaction. The formylated resorcinarene reacts easily with primary aliphatic and aromatic amines. The resulting imines exist exclusively in keto-enamine forms. Owing to a system of intramolecular hydrogen bonds, the reaction selectively leads to regioisomers with C4 symmetry. They possess an inherent chirality due to a propeller-like skeleton. For chiral amines, inherently chiral diastereoisomers are observed.

Porous Molecular Capsules as Non‐Polymeric Transducers of Mechanical Forces to Mechanophores

“…For (1 + C 60 ) milled , Figure 2. This signal disappearsd uring the procedure of removal of uncomplexed fullerenes, which is consistent with the externalp ositiono fC 60 . 13 CCP/MAS NMR spectrawith contact time10mso fa )(1 + C 60 ) mixed ,b)(1 + C 60 ) milled ,c )(1 + C 60 ) processed .…”

“…This signal is wider than the remaining two, which is attributed to the unsymmetrical environment of externally bound C 60 or its poorly defined position. This signal disappearsd uring the procedure of removal of uncomplexed fullerenes, which is consistent with the externalp ositiono fC 60 . The interpretation is also supported by 2D 1 H- 13 Ci nv-HETCOR NMR [48,49] spectra performed employing very fast magic angle spinning( VF MAS) with long contact time (10 ms).…”

“…Although the resolution is not sufficient to distinguish which of the three fullerenes ignals is involved in this correlation, we claim that the correlation comesf rom the middle signal because the analogous correlationsa re not presenti nt he reference samples (Figure 2d). Finally,t he most downfield shifted signal at d = 142.4 ppm was attributed to cavity-complexed C 60 .T his assignment is based on ac omparison of the chemical shift with the reference sample (1 + C 60 ) processed .T his signal unambiguously proves that complexation proceeds in the solid state. It hast ob es tressed that the CP/MAS sequence is not suitable for quantitative analysis( it is based on magnetization transfer from 1 Ht o 13 Cv ia dipolar interactions, which strongly depend on the distance between both nuclei and molecular dynamics).…”

“…Analogous experiments were performed for (1 + C 70 ) milled ,( 1 + C 70 ) mixed ,a nd (1 + C 70 ) processed . Owing to the D 5h symmetry,f ive 13 Cs ignals are expected for C 70 [51] andt he signals in the 13 CC P/MAS NMR spectrum are wider andl ess intense than for C 60 .F or the sample (1 + C 70 ) mixed ,t he 13 CC P/MAS NMR spectrum shows only signals of the capsule 1 even with al ong contact time (10 ms, Figure 2h). This indicates that the carbons of C 70 in the physical mixture are located too far from protons of 1 for magnetization transfer.Incontrast, for milled sample (1 + C 70 ) milled ,the signals of C 70 are clearly visible and two sets of signals can be distinguished (Figure 2i,F igure S12 in the Supporting Information).…”

Switching of inherent chirality driven by self-assembly

“…8,9 The tautomerization proceeds in a highly regioselective manner, i.e. [8][9][10] For aliphatic chiral amines two inherently chiral M and P diastereoisomers were clearly visible in NMR spectra and chemical exchange between them was slow on the NMR timescale (EXSY, no exchange detected using a mixing time of 1.5 s). [8][9][10] For aliphatic chiral amines two inherently chiral M and P diastereoisomers were clearly visible in NMR spectra and chemical exchange between them was slow on the NMR timescale (EXSY, no exchange detected using a mixing time of 1.5 s).…”