Aliphatic C–H/π and Heteroatom/π Interactions in N‐Aryl‐3,4‐(9′,10′‐dihydroanthracene‐9′,10′‐diyl)succinimides

Abstract

A series of N‐aryl‐3,4‐(9′,10′‐dihydroanthracene‐9′,10′‐diyl)succinimides have been synthesized as model compounds to study the interaction of an aromatic π system with aliphatic H atoms and heteroatoms such as oxygen, sulfur, and fluorine. The steric requirements of the rigid scaffold forces the N‐aryl residue and a benzene ring of the dihydroanthracenyl moiety to adopt an edge‐to‐face conformation in which one of the ortho‐substituents of the N‐aryl group interacts with the π system. The succinimides were generally obtained as mixtures of isomers and their ratios were considered as a function of the substitution pattern at the ortho positions of the N‐aryl residue. The experimentally observed ratios were in good agreement with those predicted computationally by DFT calculations at the BMK/cc‐pVDZ level of theory. From this study it was concluded that in these systems the aliphatic C–H/π interaction is mildly stabilizing and, to a certain extent, capable of overcoming unfavorable steric effects. On the other hand, the interaction of a π system with oxygen, sulfur, or fluorine atoms was destabilizing. When methyl or ethyl groups were allowed to compete with oxygen and fluorine for interaction with the benzene ring, C–H/π interactions were consistently observed to preferentially occur despite unfavorable steric effects.

Some Recent Advances in the Design and Use of Molecular Balances for the Experimental Quantification of Intramolecular Noncovalent Interactions of π Systems

“…It is likely that the R-endo (or folded) conformer is destabilised by steric and electronic repulsions,a nd hence the strengthofany favourable interaction of an Rs ubstituent with the p-system mustb e weighed against these repulsions. In spite of this inherent design limitation, it is possible to attenuate the electronic character of the N-aryl group throughi ncorporation of an Xg roup, and, as exemplified in ab eautiful study by Cozzi and co-workers [22] to probe the CH···p interaction of am ethyl substituent R. Although this molecular balance is structurally similar to that by Wilcox et al, [14] the principal advantage of the balance based on the N-arylamide unit is that it allows monitoring of the two distinct folded and unfolded conformations about an imide bond by direct integration of 1 HNMR spectra.…”

“…Surprisingly,t he very first examples of NMRm easurements of the restricted N-aryl bond rotation in N-ortho-aryl substituted succinamides ( Figure 5) [22] date back over 40 years to as eminal paper by Verma and Singh. [23] Due to the restrictionsi mposed by the rigidm olecular frame and the proximity of the two carbonyl groups, the N-aryl group is approximately perpendicular to the aromatic ring of the 9,10-dihydroanthracene base, adoptinga ne dge-to-face alignment.…”

“…Most recently,f ollowing on from our detailed comparison of "oxygen versus sulphur" over aw ide range of p systems, [26a,e] the Shimizu group have reproduced the isolated measurement previously made by Cozzi [22] and published their own detailed study of the interactions of 18 pairs of ethers and thioethers with an extended series of polycyclic aromatics. [27] Even althought he authorsw ere aware that the ether or thioether group is placed at shorter than the optimum distance above the aromatic surface and that this inherent steric bias favours the smallero xygen atom, the significant observation was made that, in almosto ne third of the cases studied, the larger sulfur atom is favoured over the oxygen atom in the folded conformation.…”

Anthracene-fused isoxazolopyrrolo[2,1- a ]isoquinolines via an endocyclic N -acyliminium ion cyclization: a joint experimental and theoretical study

“…28-(p-Tolyl)-30-oxa-12,29-diazaoctacyclo-[13.6.6.3 2,14 .0 2,14 .0 3,12 .0 4,9 .0 16,21 .0 22,27 ]triaconta- 4,6,8,16,18,20,22,24,26,28-decaen-13- 2,14 .0 2,14 .0 3,12 .0 4,9 .0 16,21 .0 22,27 ]triaconta- 4,6,8,16,18,20,22,24,26,28-decaen-13-one (22d). 16 mg (91 %) yield (m. p. 117−120 ºС, methanol) as yellow solid.…”

“…N-Substituted 3,4-(9',10'-dihydroanthracene-9',10'-diyl)succinimides have been used as model compounds to study the interaction of an aromatic π system with aliphatic H atoms and heteroatoms such as oxygen, sulfur, and fluorine. 22 Maleimide cycloadducts of anthracene derivatives can evolve into the realization of valuable molecular probes for imaging applications based on fluorescence photoactivation. 23 Thereby the development of simple, efficient and effective synthetic methods for compounds containing pyrrolo[2,1-a]isoquinoline, isoxazole and anthracene structural fragments is still an important and actual challenge of organic chemistry.…”