The Original Synthetic Pathway

The most bulky phosphine P-/-Bu3 does not produce a binuclear compound at all on reaction with 1,2, or 3. Under various conditions, the only product is Pd(P-f-Bu3)2. This complex, first described by Otsuka et al. (12), is particularly inert toward C5H5Pd(all), although the metal has only a 14-electron configuration. The sterically demanding P-f-Bu2Ph behaves 

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Overall, this route from 48 to 62 is three steps shorter than the original synthetic pathway and gives an improved yield of 49%. Final steps entailed the cleavage of the Boc-group and subsequent cis selective Lindlar hydrogenation of the triple bond to complete the total synthesis of (+)-astrophylline. 

Based on this information, it was decided that a group of 2-(4-methoxyphenyl)-3//-naphth[l,2-c/]imidazoles substituted differently at N-3 should also be synthesized using the same reaction pathway. It was found that the original synthetic pathway did not work for the unsubstituted derivative. Attention was therefore focused on an alternate pathway involving the hydrogenation of 2-amino-1-nitronaphthalene to 1,2-naphthalenediamine (Scheme HI). 

N-Hydroxy-N-nitrosamines with an aliphatic group at O2 produce a compound stable to aqueous acid and base (Fig. 3.4, 29) [158], whereas all other N-hydroxy-N-nitrosamines are susceptible to hydrolysis and appropriate 02-derivatives also render these materials vulnerable. The hydrolysis endpoint is the formation of nitroxyl (HNO) [which dimerizes to form nitrous oxide (N20)] and a C-nitroso compound. These products are formed from aryl [159] and alkyl bound unsubstituted diazenium-diolates as well as Oralkylated derivatives [160]. Studies of the solvolysis of Oi-alkyl derivatives are complicated by their tendency to decompose via competing radical pathways [161], but the Oi-benzyl derivatives are unique in that they hydrolyze back to the original synthetic precursors (Scheme 3.14) [162]. 

This selection of diverse MCRs developed in the last 5 years clearly illustrates the high synthetic potential of 1,3-dicarbonyl derivatives in heterocyclic chemistry. These very easily accessible and versatile substrates can be accommodated in many original synthetic pathways. Therefore, they have found numerous applications, especially for the synthesis of complex heterocyclic structures, allowing the facile... 

Another fruitful source for identifying possible structures comes from knowing the sample s origin. Was the sample extracted from a mother liquor, isolated from a bulk lot, or synthesized from precursors It is useful to know both the original synthetic route as well as the isolation pathway followed to prepare the sample. Not only will this provide clues of the possible structure based on predicted chemistry, it will also reveal any potential contaminants in the NMR sample. This will be important if the sample purity is low. Some examples of common contaminant sources include parent compound, precursors, catalysts, stereoisomers, excipients, extractables, and reaction vessel. 

CdSe is a compound II-VI semiconductor composed of Cd + and Se ions. In the original synthetic procedure described by the Bawendi group, dimethyl cadmium [(Me)2Cd] and tri-n-octylphosphine selenide (TOPSe) were used as the precursors for Cd and Se, respectively. Later, other cadmium compounds such as cadmium acetate [Cd(Ac)2] and CdO were used alternatively, because (Me)2Cd is extremely toxic and pyrophoric. Although the exact reaction pathway has not been clearly elucidated, it is thought that atoms of Cd and Se are released via the thermal decomposition of the precursors. 

Original Synthesis. The first attempted synthesis of i7-biotin in 1945 afforded racemic biotin (Fig. I). In this synthetic pathway, L-cysteine [52-90-4] (2) was converted to the methyl ester [5472-74-2] (3). An intramolecular Dieckmaim condensation, during which stereochemical integrity was lost, was followed by decarboxylation to afford the thiophanone [57752-72-4] (4). Aldol condensation of the thiophanone with the aldehyde ester [6026-86-4]... 

This Part of the book could as well have been titled "Synthesis in Action" for it consists of specific multistep sequences of reactions which have been demonstrated by experiment to allow the synthesis of a variety of interesting target molecules. Graphical flowcharts for each synthesis define precisely the pathway of molecular construction in terms of individual reactions and reagents. Each synthetic sequence is accompanied by references to the original literature. 

The structure elucidation of the kinamycins was a formidable challenge, and the information presented below draws from the work of several research groups over a period of more than 20 years. As will be shown, the originally proposed structure of the kinamycins contained a cyanamide rather than a diazo function. Subsequent synthetic and biosynthetic studies led to replacement of the cyanamide with a diazo function. The structural elucidation was challenging, in part, because of the high degree of unsaturation of the kinamycins, which limits the utility of H and 2D NMR analysis. In addition, because these structures were unprecedented, there were no clear benchmarks for comparison at the time. The pathway from isolation to determination of the correct structure is described below. 

Concept The basic concept is to study cell biological phenomena with an approach originating from organic chemistry. Based on structural information available for a given biological phenomenon unsolved chemical problems are identified and new synthetic pathways and methods are developed. This new chemistry then is used to synthesize tools for subsequent biological investigations. If... 

As commented previously, alkenyl(amino)allenylidene ruthenium(II) complexes 41 are easily accessible through the reaction of indenyl-Ru(ll) precursors with ynamines (Scheme 10) [52-54]. Based on this reactivity, an original synthetic route to polyunsaturated allenylidene species could be developed (Scheme 19) [52, 53]. Thus, after the first ynamine insertion, complex 41 could be transformed into the secondary derivative 62 by treatment with LiBHEts and subsequent purification on silica-gel column. Complex 62 is able to insert a second ynamine molecule, via the cyclization/cycloreversion pathway discussed above, to generate the corresponding dienyl(amino)allenylidene species. Further transformations of this intermediate in the presence of LiBHEts and Si02... 

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