Analogous synthetic approach

An analogous synthetic approach that uses Ni(0)-catalyzed dehalogenative polycondensation. yielded, for example, yellow polymers 151 with = 8,000-13,600 and PDI = 1.3-2.1 by GPC (Equation (54)). " Comparison of the UV-VIS spectrum for the polymer with that for the model dimer was consistent with the presence of a... 

An analogous synthetic approach has been used by Fox et al. [SO] for the preparation of CdSe/ZnSe core-shell particles. X-ray photoelectron and Auger and absorption spectroscopies were applied to demonstrate the assumed structure of both composites, CdSe on ZnSe and ZnSe on CdSe. It is found that the shell material dominates the optical properties of the particles, even when the narrower bandgap material was used for the core. This apparent contradiction to the above-mentioned statement of Brus et al. on the composite ZnS on CdSe is probably due to different sizes and different core-to-shell ratios in the two studies. 

Also of relevance at this juncture due to the analogous synthetic approach, ROMP of [4]ferrocenophane 3.61 (R=H) with unsaturated -C=C-C=C- bridges (Eq. 3.22) has been used to obtain related polyferrocenylenedivinylenes 3.62... 

Estrone (54, Chart 6) contains a full retron for the o-quinonemethide-Diels-Alder transform which can be directly applied to give 55. This situation, in which the Diels-Alder transform is used early in the retrosynthetic analysis, contrasts with the case of ibogamine (above), or, for example, gibberellic acid (section 6.4), and a Diels-Alder pathway is relatively easy to find and to evaluate. As indicated in Chart 6, retrosynthetic conversion of estrone to 55 produces an intermediate which is subject to further rapid simplification. This general synthetic approach has successfully been applied to estrone and various analogs. ... 

Polyfarylene vinylene)s form an important class of conducting polymers. Two representative examples of this class of materials will be discussed in some detail here. There are poly(l,4-phenylene vinylcne) (PPV) 1, poly(l,4-thienylene viny-lenc) (PTV) 2 and their derivatives. The polymers are conceptually similar PTV may be considered as a heterocyclic analog of PPV, but has a considerably lowci band gap and exhibits higher conductivities in both its doped and undoped stales. The semiconducting properties of PPV have been shown to be useful in the manufacture of electroluminescent devices, whereas the potential utility of PTV has yet to be fully exploited. This account will provide a review of synthetic approaches to arylene vinylene derivatives and will give details an how the structure of the materials relate to their performance in real devices. 

There have been a number of different synthetic approaches to substituted PTV derivatives proposed in the last decade. Almost all focus on the aromatic ring as the site for substitution. Some effort has been made to apply the traditional base-catalyzed dehydrohalogenation route to PTV and its substituted analogs. The methodology, however, is not as successful for PTV as it is for PPV and its derivatives because of the great tendency for the poly(u-chloro thiophene) precursor spontaneously to eliminate at room temperature. Swager and co-workers attempted this route to synthesize a PTV derivative substituted with a crown ether with potential applications as a sensory material (Scheme 1-26) [123]. The synthesis employs a Fager condensation [124] in its initial step to yield diol 78. Treatment with a ditosylate yields a crown ether-functionalized thiophene diester 79. This may be elaborated to dichloride 81, but pure material could not be isolated and the dichloride monomer had to be polymerized in situ. The polymer isolated... 

This synthetic approach is known from the synthesis of L M(alkene)H compounds from LnM(CO)alkane precursors and can easily be applied to the analogous silyl complexes. The Si—H bond even shows an increased activity for oxidative addition reactions [42, 43]. 

Dimethylene-2,3-dihydrothiophene (37, Figure 2.3) is the thiophene analog [38] of o-quinodimethanes and has been used to develop a Diels-Alder-based synthetic approach to benzothiophene derivatives. Generated in situ by treating the trimethylsylyl ammonium derivatives 38 or 39 with Bu4N F , it... 

A heavier analog of the 1,1-dilithiosilanes, 1,1-dilithiogermane derivative 57 Li2, was synthesized recently employing the same synthetic approach reduction of germacyclopropenes with metallic lithinm (Scheme 2.54). ° In contrast to the monomeric dilithiosilane 55 [Li+(thf)]2, dilithiogermane has an unusual dimeric structure in the crystalline form, 57 [Li (thf)2]>2, in which both Ge atoms are not tetrahedral, but pentacoordinated, being bonded to the two Si atoms of snbstitnents and three Li atoms. 

The cationic carbene-mercury complex 22 was prepared more than 30 years ago (3) via the reaction of 1,3-diphenylimidazolium perchlorate 5 (R = Ph R = H) with mercuric acetate. The same synthetic approach has been used more recently for the preparation of the analogous l,3-dimethylimidazol-2-ylidene complex, 23 (20). Thus, although 22 possesses a linear carbene-Hg-carbene skeleton (21), that of 23 is distorted toward a tetrahedral arrangement (C(carbene)-Hg-(C(carbene)) = 161.4(3)°) due to interactions with the chloride anions... 

This synthetic procedure steps a-d can be performed as a one-flask process. The simplicity of this method and its high yield observed makes this approach competitive with the most widely used method based on sulfuriza-tion of phosphite intermediate prepared on phosphoroamidite route. An analogous dithiaphospholane approach was applied earlier for the synthesis of phosphorodithioates derived from deoxyribonucleosides [105]. The oxathiophospholane strategy which allows stereoselective synthesis of P-chi-ral thioanalogues of oligonucleotides was most recently described by Guga, Okruszek and Stec [105]. 

The same synthetic approach is also applicable for the preparation of analogous N/N- and N/C-substituted allenylidenes 7-10 (Fig. 4) by using C-ethynylimines, such as HC=CC(=NMe)Ph, 2-ethynylpyridines, 2-ethynylquinoline, or 2-ethynyl-pyrimidine, instead of propynoic acid amides [29, 30]. 

A variant on the ship-in-a-bottle approaches described above is to react a preformed catalyst with the zeolite framework. This is analogous to procedures developed for immobilizing organometallic and coordination compounds on surfaces, but occurs within zeolite pores. These compounds that have reacted with the external surface must be removed, along with those adsorbed on the surface, to produce a true single-site catalyst. Two examples, illustrating different synthetic approaches, are discussed below. 

Yet another interesting idea concerns a possible novel synthetic approach to analogs of the unusual natural products FR-900848 296 and U-106305 297 (Fig. 10) [162]. 

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