Synthesis donor- acceptor interactions

An expedient and stereoselective synthesis of bicyclic ketone 30 exemplifies the utility and elegance of Corey s new catalytic system (see Scheme 8). Reaction of the (R)-tryptophan-derived oxazaboro-lidine 42 (5 mol %), 5-(benzyloxymethyl)-l,3-cyclopentadiene 26, and 2-bromoacrolein (43) at -78 °C in methylene chloride gives, after eight hours, diastereomeric adducts 44 in a yield of 83 % (95 5 exo.endo diastereoselectivity 96 4 enantioselectivity for the exo isomer). After reaction, the /V-tosyltryptophan can be recovered for reuse. The basic premise is that oxazaborolidine 42 induces the Diels-Alder reaction between intermediates 26 and 43 to proceed through a transition state geometry that maximizes attractive donor-acceptor interactions. Coordination of the dienophile at the face of boron that is cis to the 3-indolylmethyl substituent is thus favored.19d f Treatment of the 95 5 mixture of exo/endo diastereo-mers with 5 mol % aqueous AgNC>3 selectively converts the minor, but more reactive, endo aldehyde diastereomer into water-soluble... 

The polymer/SWCNT composites can be used as Scaffolds in tissue engineering. The donor-acceptor interactions can be used to assemble thin polymer/SWCNT films stepwise. This method also can be expended to more thermally and oxidatively stable polymer systems. For example, the P4VP/SWCNT films can be used as scaffolds for the synthesis of novel hybrid structures (Correa-Duaite et al., 2004). The polyethyl-enimine (PEI)-SWCNTs composites were used as a substrate for cultured neurons, and promoted neurite outgrowth and branching (Rouse et al., 2004). Correa-Duarte et al. (2004 Landi et al., 2005) reported that 3D-MWCNT-based networks are ideal candidates for scaffolds/matrices in tissue engineering. 

The synthesis of polycatenanes requires, like the synthesis of catenanes, the preorientation of the macrocycle precursors into a favorable geometry before cycliza-tion (Scheme 4) [5], This pre-orientation is commonly achieved via a template, resulting from rc-donor-acceptor interactions, hydrogen-bonding, and coordination bonds [1-3, 5, 41], The use of a template in catenane synthesis is the subject of Chapters 4 and 6-8 and will not be treated further in this section. The aim of this section is to present the state of the art of the various synthetic approaches leading to the polycatenane polymers and networks. 

We have found that chiral boronate complexes with BLA (Brpnsted acid-assisted chiral Lewis acids) to give new catalysts for enantioselective synthesis which achieve selectivity by a double effect of intramolecular hydrogen-bonding interaction and attractive ji-ti donor-acceptor interaction in the transition state by a hydroxy aromatic group [27a],... 

In order to get some information about the fate of silylenes S-la-d in the presence of a second molecule of methyl halide 6a-d, we checked whether silylenes S-la-d can experience stabilization by donor/acceptor interaction with 6a-d. Indeed, the two partners form weak donor/acceptor complexes 7a-d. That means that if S-la-d is created in a matrix at very low temperature in the presence of an excess of a methyl halide 6a-d, complexes like 7a-d should be present. Such a solvation might be the prerequisite for the direct synthesis of silanes 8a-d. These compounds represent the global minima on the CiHaSiX potential energy surfaces and are expected to be generated fl-om the two educt molecules S-la-d and methyl halide 6a-d in rather exothermic (AH, = 65-95 kcal moP ) processes. In the chlorine series (Scheme 1) the value is 73.9 kcal moP. ... 

In the case of catenanes, the most rationale synthetic strategy is the clipping of a macrocycle onto a preformed one (Fig. 8). A double-clipping procedure can also be used [46]. Figure 9 shows the synthesis of a catenane templated by electron donor/acceptor interactions [45]. Reaction of a... 

Figure 9. Synthesis of a [2]catenane templated by electron donor/acceptor interactions [45].

Donor-acceptor interactions are known for both alkyl (92,137-147) and silyl (128,148-150) groups with face-bridging carbonyls. The presence of silyl groups is noteworthy since they have not yet been observed for either edge-bridging or terminal carbonyls. The synthesis of the silicon-containing compounds is outlined in Eqs. (22) and (23). The products from Eq. (22) are... 

This methodology has been used for a simple enantioselective synthesis of (15,4/ )-Bicy-clo[2.2.1]hept-2-ene-2-methanol. [22] These results suggest a transition state 23 in which the dienophile assumes an orientation parallel to the indole ring because of the r-jr donor acceptor interaction leading to an unprecedented (200 1) enantioselectivity. [21, 23]... 

Summary The synthesis and structural characterization of (F3C)F2SiONMe2 by X-ray diffraction and quantum chemical calculations, revealed a new three-membered ring compoimd with a strong donor-acceptor interaction between silicon and nitrogen atoms. The replacement of one F atom in F3SiONMe2 by an F3C group leads to further increase in the already distinct Si--N interaction. The crystal structure of (F3C)F2SiONMe2 shows that the SiN distance [1.904(2) A] is even shorter than the covalent SiC bond [1.912(3) A]. The compound is unstable at ambient temperature and decomposes, probably with formation of difluorcarbene. 

In 1992 Anelli et al. developed a template synthesis of catenane based on electron donor-acceptor interactions. The synthesis was accomplished by stirring 1 equiv. of bis(pyridinium) salt (92). 2Pp6, 1 equiv. of 1,4-bis(bromomethyl) benzene, and 2.5 equiv. of the bisparaphenylene-34-crown-lO (93) in acetonitrile at room temperature for 48 h the catenane (94) was obtained with a remarkable 70% yield (Equation (6)) <92JA193>. An analogous [2]-catenane was formed with macrocycle (95) <93RTC429>. Polycatenanes were also synthesized <94AG(E)433>. The macrocyclic polyether tris-1,5-naphtho-57-crown-15 (96) was used to form [3]-, [4]-, and [5]-catenanes [Pg.835]

In 2008, Robinson and coworkers reported on the serendipitous synthesis of the disilicon compound Si2(NHCi PP)2 (Dipp = diisopropylphenyl), which was obtained when SiCl4 was reacted with NHCI PP [44]. The authors also presented the results of quantum ciemical calculations which suggested that the bonding situation in the molecule can be understood in terms of (NHC PP)->SiSi-(-(NHC PP) donor-acceptor interactions. In the following years, numerous analogues of the... 

Control of reactivity by activating a strong stereoelectronic effect The differences in the donor ability of heteroatoms can be used in a variety of ways. For example, it leads to a convenient synthesis of diaza[4] helicenes from tris(2,6-dimethoxyphenyl)methyl cation and primary amines (Figure 10.21). Again, the transformation is driven by favorable thermodynamics originating from a delocalizing donor-acceptor interaction between nitrogen lone pairs and benzylic cations. 

Summary In order to investigate the influence of iron-containing substituents on the redox behavior of oligosilanes a series of dicarbonylcyclopentadienyliron (Fp)- and ferrocene (Fc)-substituted silanes was subjected to cyclovoltammetric studies together with several reference compounds. UV-Vis and CV data indicate considerable donor-acceptor interaction in Fp-Si2Me4-C6H4CH=C(CN)2 (1)- Furthermore, electrochemical synthesis of Fp-substituted silanes is reported. 

Interestingly, the value of formation constant Kc of a complex with iodine has been used as a measure for evaluation of anti-thyroid activity of such compounds. The complexes of morpholine with iodine were shown to be of the n-o type with a 1 1 stoichiometry. A strong donor-acceptor interaction was found in this complex (Kc = 1261 12 moP at 20 °C in CCLt). This is considerably higher than analogous characteristics of complexes of aromatic compounds with iodine. The high value of the formation constant for this complex indicates that morpholine could serve as a starting point for the synthesis of novel anti-thyroid drugs [16]. 

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