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We describe herein a palladium-catalyzed tandem oxidative arylation/olefination reaction of aromatic tethered alkenes/alkynes for the synthesis of dihydrobenzofurans and 2 H-chromene derivatives. This reaction features a 1,2-difunctionalization of C−C π-bond with two C−H bonds using O2 as terminal oxidant at room temperature. The products obtained are valuable synthons and important scaffolds in biological agents and natural products. [ABSTRACT FROM AUTHOR]

Chemically bound structures of several benzene molecules are studied both analytically and numerically. The bonds in these structures are established by replacing the intra π-bonds of C 6 rings by the inter σ-bonds. The rearrangements of different π-bonds may take place differently which causes distortions of C 6 rings. The reason of the distortions is the pseudo-Jahn–Teller effect (PJTE). In the case of two chemically bound benzene molecules in a hollow position (with direct on-top stacking), called as bi-benzene, three different distorted states in addition to the undistorted one are found to exist. PJTE leads also to a chemical bonding of three and more benzene molecules stacked directly on-top of each other. These bound structures do not exist for undistorted molecules. All bound states, although being metastable are separated from the unbound ones by energy barriers ≳2 eV. It is found that the height of the barrier for symmetric bi-benzene is essentially affected by the Jahn–Teller effect. [ABSTRACT FROM AUTHOR]

"Synergistic effect" is prevalent in natural metalloenzymes in activating small molecules, and the success has inspired the development of artificial catalysts capable of unprecedented organic transformations. In this work, we found that the attractive π–π interaction between organic additives (as electron-donors) and the perfluorinated arenes (as electron acceptors) is effective in gold hydride catalyzed activation of C-F bonds, specifically hydrodefluorination (HDF) of perfluoroarenes catalyzed by the Sadighi's gold hydrides [(NHC)AuH] (NHC = N-heterocyclic carbene). Although a weak interaction between [(NHC)AuH] and perfluoroarenes was observed from 1H NMR and UV-vis spectroscopies, low reactivity of [(NHC)AuH] toward HDF was found. In contrast, in the presence of p-N,N-dimethylaminopyridine (DMAP), the HDF of perfluoroarenes with silanes can be efficiently catalyzed by [(NHC)AuH], resulting in mainly the para-hydrodefluorinated products with up to 90% yield and 9 turnovers. The yield of the reaction increases with the more electron-withdrawing groups and degree of fluorination on the arenes, and the HDF reaction also tolerates different function groups (such as formyl, alkynyl, ketone, ester, and carboxylate groups), without reduction or hydrogenation of these function groups. To reveal the role of DMAP in the reactions, the possible π–π interaction between DMAP and perfluoroarenes was suggested by UV-vis spectral titrations, 1H NMR spectroscopic studies, and DFT calculations. Moreover, 1H and 19F-NMR studies show that this π–π interaction promotes hydrogen transfer from [(NHC)AuH] to pyridyl N atom, resulting in C-F bond cleavage. The interpretation of π–π interaction assisted C-F activation is supported by the reduced activation barriers in the presence of DMAP (31.6 kcal/mol) than that in the absence of DMAP (40.8 kcal/mol) for this reaction. An analysis of the charge distribution and transition state geometries indicate that this HDF process is controlled by the π–π interaction between DMAP and perfluoroarenes, accompanied with the changes of partial atomic charges. [ABSTRACT FROM AUTHOR]

Although weak interactions play subtle but important roles in dictating protein structures, their experimental detection is nontrivial. From NOE experiments we provide direct evidence for the presence of CH···π interaction, operational between the Cα-H of the first Pro and the aromatic (Aro) side chain of Xaa, in a peptide series with the general sequence Ac-Pro-Pro-Xaa-NH2. Indirect evidence of CH···π interaction is provided from ring current-induced upfield displacement of Pro(1) Cα-H chemical shifts and restriction of side-chain (χ1) rotation of Xaa. A consequence of this interaction is the enhanced stability of the Pro-cisPro conformer in Ac-Pro-Pro-Xaa-NH2 when Xaa is aromatic. The free energies associated with trans to cis transformation of the Pro-Pro moiety are 0.35, 0.59, 0.64, and 0.82 kcal/mol when Xaa is Tyr, Trp, Phe, and His (pH of 8.4), respectively. In comparison, the corresponding free energy is ~1.55 kcal/mol when Xaa is nonaromatic. The observed population of Pro-cisPro-His and the pH-induced perturbation of electron density of the His side chain were correlated, providing further evidence for a direct role of CH· · ·π interaction in modulating the stability of Pro-cisPro population in Ac-Pro-Pro-Aro-NH2. Our study establishes Pro-Pro-Aro to be a new sequence motif that can stabilize Pro-cisPro peptide bonds. This study not only identifies a new structurally biased sequence motif but also directly demonstrates the role played by CH· · ·π interactions in subtly altering conformational preferences of three-residue peptide sequences with implications on the role played by cis-peptide bonds in unfolded proteins. [ABSTRACT FROM AUTHOR]

The article discusses research by Fukino et al. in the same issue on the assembly of ferrocene-based nanotubes using π-stacking and metallophilic interactions. Topics include the harnessing of noncovalent interactions for chemical science research, the stability and disassembly of the nanotubes, and the implications of the findings on further research in the field.