Organic synthetic precursors

Thus, as this example clearly shows, reagent 36 (and 37 as well)3c.h Is sufficiently enantioselective to control the stereochemical outcome of reactions with aldehydes that possess only modest intrinsic diastereofacial preferences. The consequences of this increased selectivity for organic synthesis are obvious. In the present case, compounds 29 and 30, which are synthetic precursors to 2-deoxyribose and 2-deoxylyxose,i7b are each now easily prepared with excellent selectivity from readily available precursors. 

For a recovery of (S)-a,a-diphenylprolinol, which is the hydrolysis product of the CBS-catalyst (S)-5 (and likewise its synthetic precursor ), the aqueous phase is carefully adjusted to pH 10 with concentrated ammonia and extracted with diethyl ether (3 x 50 ml). The combined organic layers are washed with brine (50 mL) and dried over MgS04. Removal of the solvent by rotary evaporation yields 1.68 g (79%) of crude (S)-a,a-diphenylprolinol. This material is dissolved in dichloromethane / methanol 9 1 (3 ml) and filtered over Alox B (act. Ill, 80 g) with dichloromethane / methanol 9 1 as the eluent, to yield 1.64 g (77%) of (S)-a,a-diphenylprolinol as a white solid. 

Allenes are versatile synthetic precursors in organic chemistry and the synthesis of many natural products involves the use of allenic compounds [27]. However, they have received much less attention than alkenes or alkynes for transition metal catalyzed reactions. The explanation lies in the problems of selectivity that these substrates display as a result of their reactivity and their inherent chirality [28]. 

The complex is a brown solid, highly insoluble in most organic solvents. It is thought to have a polymeric chloride-bridged structure.12 It reacts via halogen-bridge cleavage and is a synthetic precursor to a variety of ruthenium(II) complexes.11... 

The most abundant simple carbohydrate, and indeed the most abundant pure organic chemical, is sucrose. Its central role as a nutritive sweetener is well documented, but its potential as a precursor for organic synthetic manipulation (sucrochemistry) has long been a story of largely unrealized potential. The article here by Queneau (Lyon), Jarosz (Warsaw) and their coauthors provides a comprehensive account of actual and potential uses of sucrose as a cheap precursor for a range of applications as food additives, pharmaceuticals, surfactants, and complexing agents. The authors assess fundamental questions of... 

Pseudohalides, such as thiocyanates, should also receive some attention in the future. Because of their dual ligation mode, they might be used as specific synthetic precursors [121]. Like Ln-halides [122], they have been successfully employed as catalysts in organic transformations [123]. 

PPV derivatives can be prepared by water-soluble precursor route [14-16] involving sulfonium polyelectrolyte or organic-soluble precursor route [3,17,18] involving alkoxy substituted non-ionic form, respectively. The representative synthetic pathways for PPV derivatives are shown in Scheme 1. 

Organic halogen compounds have been used as synthetic precursors in electrochemical synthesis. They can be converted into aldehydes, ketones, alcohols and may be coupled with C—C bond formation in each case. Since this area is the subject of another chapter in the present volume (by Casanova and Prakash Reddy) the coverage here entails a brief description of synthetically useful coupling reactions that have been reported recently. 

The preparation of metalated dienyl derivatives is still a challenging problem in organic synthesis as only a few examples are reported in the literature. Since dienyl metals could be very useful synthetic precursors, efficient preparative methodologies opening new routes to stereodefined and functionalized systems would have a large number of synthetic applications. 

The purpose of this subsection is to define for a given synthon S(A) its synthetic precursor and/or successor (SPS) in such a way that this term will be closely related to the reasoning of organic chemists. An organic synthesis of a product compound M from an educt compound M is usually realized not in one step but it is carried out through a multistage synthetic procedure, schematically... 

Triorganyltelluronium salts, RsTeX, have been known for over a century. In recent years, they have attracted considerable interest because of their role in organic synthetic chemistry For example, it has recently been reported that the telluronium salts are precursors for telluronium ylides that react with the carbonyl compounds, forming a variety of products like oxiranes and secondary alcohols. ... 

Optically active cyanohydrins are synthetic precursors of a-hydroxy carboxylic acids, a-amino carboxylic acids, /1-hydroxy amines, and several other classes of organic compound of biological importance [146]. Several efficient catalysts have been developed by using titanium as the central metal. 

Structural analysis of an unknown organic material normally begins with an examination of the and spectra. Resonance positions are analyzed, if possible, with the benefit of knowledge of the molecular formula and structural information based on synthetic precursors. Representative chemical shifts are given in Tables 3-8 through 3-12, drawn from references at the end of this chapter. 

Optically active aldehydes are desirable synthetic precursors for the construction of chiral carbon skeltones in organic synthesis. Several methods had been devised for the synthesis of optically active aldehydes employing chiral enamines chiral imines or chiral hydrazone however, little was known about the asymmetric synthesis of chiral aldehyde having a functional group in the same molecule... 

CoCp(CO)2 also is a versatile synthetic precursor, which reacts with a wide variety of organic compounds. It serves as a source of the reactive CoCp unit, and this species catalyzes cyclization of alkynes as well. This reaction has been applied to the one step synthesis of steroid analogs [22]. 

The general concept is that sulfur is introduced into the organic substrate as a direct synthetic precursor of fluorine. Tlte sulfur compound is then treated with a thiophilic, soft electrophilic oxidant, for example electrophilic halogenation agents (NBS, NIS, DBH, Br2, SO2CI2 [148], Fj [149], IF5 [150], BrFj [151], 4-MePhIF2 [152], or nitrosyl cations (NO BF., ) [146] in the presence of a fluoride source (50% or 70% HF-pyridine [143], HF-melamine [144], NEt3 3HF) [147]. 

Upon treatment with sodium nitrite and hydrochloric acid at 0°C, primary aromatic amines can be converted to aromatic diazonium salts, an unstable species that is very useful in organic synthesis. Since a nitro group can be reduced to a primary amine, it is a synthetic precursor to a diazonium salt. 

The complex (pyH)2(CeCl6) has been discussed as an alternative Ce(IV) precursor [72]. Pseudohalides such as thiocyanates should receive some attention as specific synthetic precursors due to their dual ligation mode [73]. Like the halides [74], their Ln(III) derivatives have been successfully employed as catalysts in organic transformations [75]. 

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