CH/Jt interactions

Mataka and coworkers reported the studies of the Diels-Alder reactions of [3.3] orthoanthracenophanes 96 and 97, of which anthraceno unit, the potential diene, has two nonequivalent faces, inside and outside. The reactions of 96 with dien-ophiles gave the mixtures of inside and outside adducts with the ratios between 1 1 and 1 1.5. However, the ratio changes drastically, in favor of the inside adducts, when 97 reacts with dienophiles such as maleic anhydride, maleimide and naphto-quinone [55] (Scheme 46). Mataka suggested that the Jt-facial selectivity is controlled by an orbital interaction between the electron-poor dienophiles and the Jt-orbital of the facing aromatics, which would lead to a stabilization of the transition state, while Nishio suggested that the selectivity is due to the attractive k/k or CH/jt interaction [53]. 

M. Nishio, M. Hirota and Y. Urezama, The CH/jt Interaction. Evidence, Nature, and Consequences, Wiley-VCH, New York, 1998. 

Catenane formation from fluorinated ligand 19 is apparently more effective than that from 12. This difference is most probably because of attractive edge-to-face or CH-jt interaction working in catenane 13, as observed in the crystal structure of platinum-incorporated catenane 14 (Figure 2). In this structure, we can observe efficient edge-to-face aromatic contacts between two phenylene units or a phenylene and a pyridine ring. 

Chiral quaternary alkanes do not have any m-electrons or a heteroatom. Thus, the present chiral discrimination may involve the CH-7T interactions between the CH group of the chiral hydrocarbon and the m-electrons of the pyrimidine-5-carbaldehyde 11. This CH-jt interaction [109] maybe used to discriminate between the Re and Si enantiofaces of aldehyde 11, because the... 

Nishio M, Hirota M, Umezawa Y (1998) The CH/jt interaction— evidence, nature, and consequences, Chapt 11. Wiley-VCH, New York, p 175... 

In the study of isozyme-selective modulators for protein kinase C (PKC), docking simulations of the benzolactam 16 (BL-V8) with the crystal structure of the PKCd) C1B domain were performed using the FlexX program in SYBYL <2005JA5746>. The data provided evidence that the CH-Jt-interaction plays a pivotal role in the binding of 16 to the PKC5 C1B domain. The binding affinity was enhanced in the naphtholactam 17 (NL-V8) by the effective manipulation of the CH-7l-interaction. 

Matsumoto, A., Tanaka, T., Tsubouchi, T., Tashiro, K., Saragai, S. and Nakamoto, S. (2002) Crystal engineering for topochemical polymerization of muconic esters using halogen-halogen and CH/jt interactions as weak intermolecular interactions. J. Am. Chem. Soc., 124, 8891-8902. 

Weakly polar interactions in proteins and protein-ligand complexes are frequently phenomenologically analyzed and classified in terms of the interacting partners [29]. This especially includes interactions with Jt-systems, such as the NH-jt, OH-jt, or CH-Jt interaction [30, 31], aromatic-aromatic interactions (parallel jt-jt stacking versus edge-to-face interaction), and the cation-jt interaction [32]. All of these can... 

Fig. 4 CH/jt interactions observed in human growth hormone-binding protein (PDB code 3HHR) Lys2l5/Tyr222/Arg213/Phe225/ Arg211/Trpl86/Lysl79 (From Ref [68J, Fig 10.)...

DFT calculations revealed the role of aromatic interactions in the additions of aryl-substituted silyl enol ethers to a chiral oxazolinium ion. Aryl-substituted silyl enol ethers give the opposite diastereoisomer of the adduct than do aliphatic silyl enol ethers owing to a combination of attractive cation-jr and CH-jt interactions, reduced steric repulsion, and lower torsional strain in the more crowded transition state. ... 

A recent study indicated that the stereoelectronic effect of a curved aromatic stmcture dominates the stability of endo/exo-l24-R (Scheme 41) [142]. Steric repulsion is the main factor to facilitate the conformer cxo-124-SiMe3, whereas some mono-substituted sumanenes, such as methylsumanene 124-Me, hydroxy-sumanene 124-OH, and 2,6-xylylsumane 124-xyl, favor formation of the stable enrio-conformation. In methylsumanene and hydroxysumanene, the hyperconjugation between the benzylic proton and the sumanenyl convex face causes the endo conformer to be more stable than the exo conformer. In 124-xyl, the CH-jt interaction, which is caused by the methyl group in xylyl substituent and the concave face of sumanene, favors the cnrto-conformer. 

Recently, Wills and co-workers (344) studied the application of ruthenium catalysts of the Noyori-type catalyst containing W-alkylated TsDPEN derivatives bearing alkyl groups of different size as the chiral ligand for the reduction of cyclic imine I (Fig. 94). The authors suggest that a viable model for the reduction of this imine (Fig. 96) could involve a protonated imine with a transition state allowing the CH-jt interaction between the aryl group of the iminium cation and the arene coordinated to the ruthenium. 

We investigated alkane recognition by a monomeric per-methylated pil-lar[5]arene H5.2 and pillar[5]arene dimer H5.17, which was prepared by connecting two mono-reactive pillar[5]arenes through a linker. Determination of the K value of the complex between H5.2 and n-hexane was difficult owing to the weak host-guest complex. In contrast, the K value between the dimer H5.17 and n-hexane determined by NMR titration was 98 12 M (run 92). The dimerization is useful for enhancing CH/jt interactions between pillar[5]arenes and alkanes. 

Begbeider, A., Linares, M., Devalckenaere, M., Degee, P., Claes, M., Beljorme, D., Lazzaroni, R., and Dubois, P. (2008) CH-Jt interactions as the driving force for silicone-based nanocomposites with exceptional properties. Adv. Mater., 20, 1003-1007. 

The high binding constants of these host-guest complexes were attributed to the formation of electrostatic interactions between the ammonium cations of the guest molecules and the carboxylate anions on the rims of the pillar[5]arenes, together with the formation of multiple CH/jt interactions between the alkyl chains of the alkyldiamine guests and the pillar[5]arenes. 

With the above in mind a series of bis-H4C[4]s containing flexible alkyl tethers (propyl to decyl) were synthesised and their coordination chemistry explored [42]. Full characterisation of these new ligands was carried out as standard, but it was only possible to isolate single crystals that were suitable for X-ray diffraction studies in one case, this being the acetonitrile solvate of H4C[4]-(CH2)3-H4C [4] (Fig. 25.7a). The asymmetric unit (ASU) comprises one molecule of H4C [4]-(CH2)3-H4C[4] and four MeCN of crystallisation, two of which occupy H4C [4] cavities, forming CH-jt interactions with the aromatic rings. 

The crystal structure of the first buckybowl, corannulene 1, was reported in 1971 [24]. It shows the noncolumnar crystal packing structure where the CH-Jt interaction rather than the Jt—Jt stacking interaction is the main factor... 

---