Selected Syntheses

In this section the syntheses of several typical siderophores will be presented in a summarized form pointing out interesting features. 

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Another of the few selective syntheses of aLkylpyridines is one for a-picoline (2) (76). This is a two-step process (eq. 24) where acrylonitrile is used to monocyanoethylate acetone in the Hquid phase at 180°C and at autogenous pressure, 2 MPa (300 psig). The monoadduct, 5-cyano-2-pentanone, is then passed over a palladium-containing catalyst to reduce, cyclize, and dehydrogenate, in sequence. 

Pharmaceutical manufacturers began to develop technologies either to resolve or selectively synthesize enantiopure drugs. The justification was that the active enantiopure drug would prove to be more efficacious, and this would allow drug companies to extend expiring originator patents. 

Table 8 gives a survey on some selected Syntheses of (partly) open chain sulfones from sulfenes. 

Scheme 3 Selected syntheses of heterocycles using polymer-supported reagents...

Dynamic kinetic resolution of racemic ketones proceeds through asymmetric reduction when the substrate does racemize and the product does not under the applied experimental conditions. Dynamic kinetic resolution of a-alkyl P-keto ester has been performed through enzymatic reduction. One isomer, out of the four possible products for the unselective reduction (Figure 8.38), can be selectively synthesized using biocatalyst, and by changing the biocatalyst or conditions, all of the isomers can be selectively synthesized [29]. 

Bromo compounds are useful intermediates for the synthesis of a range of more complicated organic compounds via direct substitution or by prior conversion into organometallic reagents. They therefore hold a key position in the synthesis of fine chemicals. This position demands that more selective methods for the synthesis of bromo compounds also be developed. In this report we have illustrated the development of selected syntheses of bromoaromatic compounds and demonstrated new ways in which they can be applied in synthetic procedures. 

When the nitrogen of the substrate contains a chiral R group, both the Stork enamine synthesis and the enamine salt method can be used to perform enantio-selective syntheses. " ... 

In recent years advances in the chemistry of leuco dyes have taken place particularly in the areas of structural identification by means of H- and 13C-NMR and selective syntheses of aminoquinones, etc. New applications of leuco quinones such as in electro-optical devices and information recording media have enhanced their importance. In these applications, the chemistry of leuco quinones is interesting mainly due to switching from a colored to a colorless system by a redox process. 

If y-Fe203 could be selectively synthesized, this could be a method of obtaining magnetic coatings. 

The parent methylenecyclopropane (MCP) (1) [1 ] is a highly volatile compound (bp 11 °C) which can be prepared in multigram quantities and is commercially available. Numerous efficient and straightforward syntheses of the different types of methylene- and alkylidenecyclopropanes have appeared in the literature and the matter has been reviewed by Binger and Buch [2]. In the last decade other selective syntheses have been developed which gave easy access to compounds containing specific substitution patterns [3], to optically active derivatives [4], or more sophisticated derivatives like dicyclopropylideneethane (2) [5], bicyclopropylidene (BCP) (3) [6] and chloromethoxy carbonyl-methylenecyclopropane (4) [7],... 

A wide variety of benzotrichalcogenoles are selectively synthesized in good yields by the reactions of the corresponding benzodichalcogenastannoles with an S or Se source (Scheme 16).126 128 Unsymmetrical tetrathiafulvalenes and diselenadithiafulvalenes are prepared by the reaction of dichalcogenastannoles with esters in the presence of AlMe3.129 131... 

For the synthesis of u-aryl-ZV-methylnitrones a silica gel-NaOH catalytic system has been used. The reaction proceeds without solvents and in good yields, irrespective of the electron-donor or electron-acceptor nature of the substituents in benzaldehyde. Under similar reaction conditions ketones do not undergo the reaction therefore, it makes it possible to carry out selective syntheses in cases where the system contains both aldehyde and ketone groups (154). 

In the very recent past, metal complex catalysis has been used with advantage for the stereo- and enantio selective syntheses based on the Henry and Michael reactions with SENAs (454-458). The characteristic features of these transformations can be exemplified by catalysis of the reactions of SENAs (327) with functionalized imides (328) by ligated trivalent scandium complexes or mono-and divalent copper complexes (454) (Scheme 3.192). Apparently, the catalyst initially forms a complex with imide (328), which reacts with nitronate (327) to give the key intermediate A. Evidently, diastereo- and enantioselectivity of the process are associated with preferable transformations of this intermediate. 

The dirhodium(n)-catalyzed asymmetric C-H insertion has been recognized as a powerful procedure for the preparation of many interesting compounds.35,43,68,179 Doyle et al. developed an efficient procedure for the enantio-selective syntheses of lactams. - The acyclic terminal diazoacetamides gave moderate enantioselectivity... 

Bradley, J.S. et al., Surface spectroscopic study of the stabilization mechanism for shape-selectively synthesized nanostructured transition metal colloids, J. Am. Chem. Soc., 122, 4631, 2000. 

Selected syntheses of thiols via S-alkyl 0-f-butyl dithiocarbonates... 

A similar micromembrane (Figure 6.30) formed by TBAB on Pd/C was able to selectively synthesize biphenyls from halobenzenes using a reducing... 

Typical evolution of particle size (BCD) as a function of reactive milling time of selected synthesized powders from Table 2.15 is shown in Fig. 2.34. SEM miaograph... 

Fig. 2.34 Particle size distributions and morphology of (a) initial Mg and selected synthesized MgH powders from Table 2.15 reactively milled for (b) 20 h under HES (MglH20), (c) 50 h under HES (MglHSO), and (d)150 h under IMP2 (MgSH) [62]...

Ichikawa et al. first reported [18-20] that Pt nanoparticles are produced by the conventional dry H2 reduction of a H2PtCl6 impregnated FSM-16 sample, while Pt nanowires are selectively synthesized in the mesoporous channels by UV-... 

Reactions carried out on the surface of inorganic oxides allow convenient high-yield and selective syntheses of various metal carbonyl complexes and clusters, starting from easily available materials (Tables 16.1-16.3). The synthetic procedures are straightforward and the recovery of products is easy. Since the use of a solid as reaction medium is not Umited in the manner in solution by boiling points and by the thermal instabiUty of some solvents, it is possible to work at atmospheric pressure even at rather high temperatures. Therefore, in many cases, yields and pressure are better and lower, respectively, than those of the traditional syntheses in solution (Tables 16.4—16.6). 

Both procedures for selective syntheses of 2,6-dideoxy-a- and B-glycosides will be outlined in the aure-olic acid and also the anthracycline oligosaccharide series. 

The Wudl group also applied their method of heterofullerene formation to synthesize aza[70]fullerenes [16], Starting from the [5,6]-bridged azahomo[70]-fullerenes 19 and 20 they selectively synthesized the AA isomer 14 and the BB isomer 16, respectively (Scheme 12.5). 

These are selected syntheses from a whole range and the limited details are only intended to provide an insight into the types of synthetic methods that are employed. Any reader wishing to have further information should consult the book edited by Gunter Buxbaum as this contains more details and a list of primary reference sources for the methods of manufacture. ... 

Chitosan-stabilized Au NPs can be selectively synthesized on surfaces like poly (dimethylsiloxane) (PDMS) films using HAuC14 as precursor. The computation of surface plasmon bands (SPBs) based on Mie theory and experimental results indicates that the particles are partially coated by chitosan. The proposed mechanism implies that chitosan acts as a reducing/stabilizing agent. Furthermore, PDMS films patterned with chitosan could induce localized synthesis of gold nanoparticles in regions capped with chitosan only [110]. 

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