Synthesis directed

Since 1,5-enediones are usually obtained via pyrylium salts, syntheses of the type found in Section B, 2, a have a rather theroetical interest, save for a few special syntheses. There exist several direct syntheses of l,5-enediones, e.g., from j8-chlorovinyl ketones and j8-diketones or j8-keto esters special pathways to 1,5-enediones have also been described, namely, oxidation with lead tetraacetate or with periodic acid of cyclopentene-l,2-diols. ... 

Vanadium phthalocyanine (PcVO) is prepared from vanadium(IIl) chloride in a melt of phthalonitrile228 to which sometimes ammonium vanadate137 or molybdate229 and urea are added. Also a reaction with vanadium(V) oxide and phthalonitrile in pen tan-1-ol has been performed.230 Besides these direct syntheses, transformation of PcH2 to PcVO in refluxing dimethylformamide with vanadyl sulfate (V0S04) has been carried out.231... 

The diastereosclectivity in this particular cyclization was exploited in a number of direct syntheses of terpenes from the eudesmane type (see Table 2). By this technique tricyclic compounds can be synthesized generating three new asymmetric centers55. 

With respect to template-directed syntheses, the syntheses of oligonucleotide using polynucleotide have already been attempted62-69. However, it has not necessarily been successful yet, since the binding constant of the nucleotide monomer with polynucleotide was not large, particularly in aqueous media. 

Many block and graft copolymer syntheses involve radical polymerization at some stage of the overall preparation. This section deals with direct syntheses of... 

The Ley group also investigated the PS-base/tosyl chloride methodology developed by Brain (see above. Scheme 8) for the synthesis of 2-aminooxadiazoles from semicarbazides, especially with a view to directly synthesize 2-aminosulfonamide substituted 1,3,4-oxadiazoles, a compound class of interest for agrochemical and pharmaceutical apphcations (Scheme 10) [71]. In this case, the choice of the supported base was crucial for the result of the reaction weak bases (PS-DIEA, PS-NMM) could still afford the cyclized 2-aminooxadiazole product, but could not efficiently... 

Schmidt J.G., Nielsen P.E., Orgel L. E. Information transfer from peptide nucleic acids to RNA by template-directed syntheses. Nucleic Acids Res. 1997 25 4797- 802. 

P. S. Skell Reactions of atoms silicon and the high-boiling metals. Direct syntheses of organometallics, pp. 215-221 (10). 

The most important nanomaterial synthesis methods include nanolithography techniques, template-directed syntheses, vapor-phase methods, vapor-liquid-solid (VLS) methods, solution-liquid-solid (SLS) approaches, sol-gel processes, micelle, vapor deposition, solvothermal methods, and pyrolysis methods [1, 2]. For many of these procedures, the control of size and shape, the flexibility in the materials that can be synthesized, and the potential for scaling up, are the main limitations. In general, the understanding of the growth mechanism of any as-... 

In 1993, ten challenges faced the catalysis research community. One of these was the anti-Markovnikov addition of water or ammonia to olefins to directly synthesize primary alcohols or amines [323]. Despite some progress, the direct addition of N-H bonds across unsaturated C-C bonds, an apparently simple reaction, stiU remains a challenging fundamental and economic task for the coming century. 

Tejedor and coworkers have utilized a combination of two domino processes for a microwave-promoted synthesis of tetrasubstituted pyrroles [344]. The protocol combines two coupled domino processes the triethylamine-catalyzed synthesis of enol-protected propargylic alcohols and their sequential transformation into pyrroles through a spontaneous rearrangement from 1,3-oxazolidines (Scheme 6.183). Overall, these two linked and coupled domino processes build up two carbon-carbon bonds, two carbon-nitrogen bonds, and an aromatic ring in a regioselective and efficient manner. The tetrasubstituted pyrroles could be directly synthesized from the enol-protected propargylic alcohols and the primary amines by microwave irradia-... 

A range of direct syntheses have been performed under conditions of moderate to low dilution but have still led to isolation of the required cyclic product in reasonable to high yields. In some of these so-called direct syntheses, ions such as sodium or potassium were present in the reaction solution. It has often been suspected (and has been documented for a number of systems) that these ions may also undertake a template role. In this manner, such syntheses may fall between the extreme direct and in situ categories mentioned at the beginning of this chapter. There is little doubt that such an effect is the source of the larger-than-expected yields obtained in some syntheses of this type. Nevertheless, this is not always the case and there are further mechanisms for assisting cyclization which may operate for particular systems. For such systems, special circumstances usually appear to be present. Examples of this latter type are discussed later in this chapter. 

In this chapter, we first review the nature of the several forms of elemental phosphorus and then proceed to consider their uses for specific types of syntheses of compounds containing the carbon-phosphorus bond. Prior reviews have also been concerned with these topics.1 2 Our purpose here is to update these presentations and provide fundamentals for the practicing chemist venturing into the use of elemental phosphorus. We limit this discussion to the more-or-less direct syntheses of organophosphorus compounds from elemental phosphorus. We will consider reactions that generate monophosphorus species without C-P bonds as critical intermediates, pro-... 

The direct syntheses of D-glucosyl-L-sorboside from sucrose and L-sorbose and of sucrose from D-glucosyl-D-xyloketoside and D-fructose can be obtained in phosphate-free enzyme preparations.40 The reactions are ... 

The core polymerase continues moving along the template strand in the 3 to 5 direction, synthesizing the mRNA in the 5 to 3 direction. 

In another recent development Kojima et al. [103] mechanically milled LiH and Al without and with the TiClj additive for 24 h in a H gas atmosphere at a pressure of 1 MPa at room temperature. They found that a sm l amount of LiAlH could be directly synthesized by the mechanochemical reaction with concomitant formation of LijAlHg. The latter can be relatively easily formed by mechanochemical synthesis of LiAlH and LiH as originally reported by Zaluski et al. [71] and later by Balema et al. [104],... 

Bu, X., Feng, P and Stucky, G.D. (1997) Science, 278 (5346), 2080-2085 Feng, P Bu, X., and Stucky, G.D. (1997) Hydrothermal syntheses and structural characterization of zeolite analogue compounds based on cobalt phosphate. Nature, 388, 735-741 Feng, P Bu, X., Gier, T.E., and Stucky, G.D. (1998) Amine-directed syntheses and crystal structures of phosphate-based zeolite analogs. Microp. Mesoporous Mater., 23 (3-4), 221-229. 

Enantiomerically pure 3-amino alcohols which are important intermediates for many bioactive compounds can be directly synthesized by the ARO reaction of readily accessible racemic and meso epoxides with appropriate amines. Indeed, some simple and multifunctional p-amino alcohols have been obtained using this strategy by the promotion of chiral BINOL [30-32,88,89], salen [35,52], bipyridine [33,40,90-94] and proline-A,JV-dioxide based metal complexes [95]. However, none of these systems demonstrated the recyclability of the precious chiral catalyst. 

One major two-carbon feedstock is ethylene. From Figure 17.2, you can see that a number of the monomers are directly synthesized from ethylene. Again, while the react arrow goes directly from ethylene to the product, as noted earlier, it often takes years to develop an economical procedure to obtain the product in essentially 100% yield. Here, depending on the reaction conditions, a wide variety of intermediates and products are formed, which allow... 

Lead difluoride also can be directly synthesized from its elements, by the action of lead with fluorine. 

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