Reactions stacking interaction

In many investigations of CT, pendant redox probes interact with both bases of abase pair. However, studies of base-base charge transfer can differentiate between discrete intra- and interstrand reactions (Fig. 7). These investigations further attest to the critical role of base stacking in DNA-mediated CT. In B-DNA duplexes, stacking interactions are largely restricted to... 

Figure 5. Stacking interaction proposed in the reaction between bipy and Ni(phen)(H20)k2 immediately prior to the first bond coordination of bipy.

TT-Stacking interactions and solvation effects within the highly preorganized cleft of a bifunctional C-shaped host are believed to benefit the base-promoted conversion of 5-nitrobenzisoxazole to 2-cyano-5-nitrophenolate relative to the acetate-promoted reaction structural variation of the host has been explored. ... 

H-stacking interactions have also been exploited to orientate olefinic moieties in a geometry suitable for photochemical cycloaddition reactions, and have been invoked by Coates et al. to explain the photodimerization and photopolymerization of mono- and diolefins carrying phenyl and perfiuorophenyl groups [43]. Matsumoto et al. reported the photodimerization of 2-pyridone in co-crystals with naphthalene-substituted monocarboxyhc acids, where the stacking of the naphthalene rings provides carbon-carbon distances appropriate for [4+4] cycloaddition [44]. 

Results from these experiments indicate that the aromatic stacking interaction between complementary strands is probably not the factor responsible for the stabilization of the cross-linked product in aqueous media. Instead, the critical role played by interstrand H bonding in the stabilization of products 19-20 (and similarly 21-22) was clearly demonstrated by the high sequence specificity of the cross-linking reactions, as well as by the behavior of control strands 24 and 25 in the presence of 20. 

Alkylation Alkylation of the phenylindanone 31 with catalyst 3a by the Merck group demonstrates the reward that can accompany a careful and systematic study of a particular phase-transfer reaction (Scheme 10.3) [5d,5f,9,36], The numerous reaction variables were optimized and the kinetics and mechanism of the reaction were studied in detail. It has been proposed that the chiral induction step involves an ion-pair in which the enolate anion fits on top of the catalyst and is positioned by electrostatic and hydrogen-bonding effects as well as 71—71 stacking interactions between the aromatic rings in the catalyst and the enolate. The electrophile then preferentially approaches the ion-pair from the top (front) face, because the catalyst effectively shields the bottom-face approach. A crystal structure of the catalyst as well as calculations of the catalyst-enolate complex support this interpretation [9a,91]. Alkylations of related active methine compounds, such as 33 to 34 (Scheme 10.3), have also appeared [10,11]. 

Stacking interactions in the transition state are one factor suggested for the highly diastereoselective synthesis of syn- and anfr-aldols from the reaction of an arylsulfonamidoindanyl titanium enolate with bidentate aldehydes.56... 

In an example of a [3]-catenane formed by this methodology, the compound 7.64 is formed from the coupling of the copper(i) complex formed from the reaction of [Cu(MeCN)4]+ with one equivalent of 7.63 and one equivalent of 7.65 in 58 % yield (Fig. 7-44) The conformation of the [3]-catenane is partially controlled by intramolecular 7i-stacking interactions (Fig. 7-45). A number of other strategies have also been adopted... 

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