Reagents and transformations

This is a question of reaction planning. To answer such a problem reagents and reaction conditions have to be found that allow one to perform the desired transformation. Such a question is best answered by a query into a reaction database (see Section 5.12). 

Before the widespread availability of instrumental methods the major approach to structure determination relied on a battery of chemical reactions and tests The response of an unknown substance to various reagents and procedures provided a body of data from which the structure could be deduced Some of these procedures are still used to supple ment the information obtained by instrumental methods To better understand the scope and limitations of these tests a brief survey of the chemical reactions of carbohydrates is m order In many cases these reactions are simply applications of chemistry you have already learned Certain of the transformations however are unique to carbohydrates... 

In the presence of aprotonic organic solvents, both aromatic and aliphatic amines interact with 4-nitrophenyldiazonium in the same way. The first stage yields fast in corresponding triazenes. At the second stage, irrespective of initial amine nature, triazenes interact with an excess of diazo reagent and fonu l,3-bis(4-nitrophenyl)-triazene. Triazenes of aliphatic amines transform fast as well. In case of aromatic amines, the second stage yield depends on the inductive constants of substituents in an azo component. 

Benzylidene acetals have the useful property that one of the two C-O bonds can be selectively cleaved. The direction of cleavage is dependent upon steric and electronic factors, as well as on the nature of the cleavage reagent. This transformation has been reviewed in the context of carbohydrates.""... 

The 4-position of isothiazole is attacked by electrophilic reagents, and many simple derivatives are thus readily available by direct substitution followed, if necessary, by suitable transformation of the group introduced. For example, bromination of 3-methylisothiazole... 

An interesting appetite suppressant very distantly related to hexahydroamphetamines is somanta-dine (24). The reported synthesis starts with conversion of 1-adamantanecarboxylic acid (20) via the usual steps to the ester, reduction to the alcohol, transformation to the bromide (21), conversion of the latter to a Grignard reagent with magnesium metal, and transformation to tertiary alcohol 22 by reaction with acetone. Displacement to the fomiamide (23) and hydrolysis to the tertiary amine (24) completes the preparation of somantadine [6]. 

The /J-amino aldehyde 1. readily available from aspartic acid, is configurationally very stable. No epimerization of the stereocenter is observed upon addition of Grignard Or cuprate reagents and the transformations display relatively high levels of 1,3-asymmetric induction73. This C-3-directing effect is superimposed upon the 1,2-directing effects of the C-2-substituents (Rl). 

The costs of an intervention have to be compared with the results of this intervention (Drummond et al. 2004). These results can be outputs, outcomes, and impacts (Fig. 2). An output is the direct result of a production process. Agents of production (resources) are transformed to generate a certain commodity or service (output). For instance, equipment, reagents, and the knowledge of a laboratory technician are used to perform a certain resistance test. Other examples of outputs are contacts, admissions, or prescriptions. 

Among various modifications of the side chain of stabilized ylides [13,14] can be pointed out the preparation and transformation of the phenyliodonio a-substi-tuted phosphonium yhdes (Scheme 3) [15]. These compounds represent a potentially useful class of reagents, in which the iodonium group can be further substituted by nucleophiles such as PhSLi. 

Oxidation of chalcones with TTN has been studied in detail (95, 96), and it has been shown that the products obtained depend on the amount of reagent and the solvent employed. Oxidation with 1 equivalent of TTN in methanol, methanol-chloroform, or methanol-boron trifluoride leads to acetals of the type (XXXIV) (see also Scheme 21) in yields of 20-80%. When 3 equivalents of TTN are employed, however, and aqueous glyme containing a little perchloric acid used as solvent, the products are benzils. This remarkable transformation, which proceeds in yields varying from moderate to good (40-80%), involves three distinct oxidations by TTN, and these are outlined in Scheme 22. Each individual step in this reaction sequence has been investigated in detail, with the result that useful procedures have been developed for the oxidation of both deoxybenzoins and benzoins to benzils with TTN (96). 

Cross-coupling reactions resulting in C-C bond formation are normally classified according to the nature of the organometallic reagent and the organic electrophile. Scheme 6.4 summarises, broadly, the names and reaction partners of the most common of these transformations. 

In summary, we have described a novel and efficient synthesis of thienobenzazepine derivatives in which the key transformation includes a telescoped process involving a selective intro reduction followed by palladium-mediated intramolecular amidation. The process developed is quite amenable for preparative scale (multi-gram) and presents significant advantage to those reported previously with respect to overall yield (e.g., 50% vs. 17% overall yield), total number of synthetic transformations (4 vs. 9), and reagents and/or conditions that are suitable for large-scale synthesis. 

The oxidation of alcohols is an important reaction in organic chemistry. While this transformation is traditionally performed in organic solvents, the use of aqueous orgarric solutions has just recently become a field of intense study (1-6). The effect of water on transition metal-catalyzed reactions, however, remains widely unexplored as most of these reactions require dry organic solvents to avoid decomposition of the transition metal catalyst, of water sensitive reagents, and/or intermediates by a nucleophilic attack of water (1). Comparative studies focusing on the effect of water as a co-solvent on the catalyst and the proceedings of a reaction are therefore rare (7). 

Indicate reagents and approximate reaction conditions that could be used to effect the following transformations. More than one step may be required. 

Either because of potential interference with other functional groups present in the molecule or because of special structural features, the following reactions require careful selection of reagents and reaction conditions. Identify the special requirements in each reactant and suggest appropriate reagents and reaction conditions for each transformation. 

The initial products of such additions under aprotic conditions are organosamarium reagents and further (tandem) transformations are possible, including addition to ketones, anhydrides, or carbon dioxide. 

The following syntheses were carried by short tandem reaction sequences starting with the Diels-Alder reaction shown. Show the reagents and approximate reaction conditions required to complete the transformation. 

Indicate appropriate conditions and reagents for effecting the following transformations. Identify necessary co-reactants, reagents, and catalysts. One-pot processes are possible in all cases. 

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