Reagents and Reaction Conditions

Phosphonium ylides are typically prepared by the reaction of a phosphonium salt with a base. Non-stabilized ylides require a strong base (such as BuLi) under inert conditions, while stabilized ylides require a weaker base (for example, alkali metal hydroxides in aqueous solution). For more detail on the variety of bases and reaction conditions that can be used in the Wittig reaction, see references [2] and [5], 

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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). 

Since (A) does not contain any other functional group in addition to the formyl group, one may predict that suitable reaction conditions could be found for all conversions into (A). Many other alternative target molecules can, of course, be formulated. The reduction of (H), for example, may require introduction of a protecting group, e.g. acetal formation. The industrial synthesis of (A) is based upon the oxidation of (E) since 3-methylbutanol (isoamyl alcohol) is a cheap distillation product from alcoholic fermentation ( fusel oils ). The second step of our simple antithetic analysis — systematic disconnection — will now be exemplified with all target molecules of the scheme above. For the sake of brevity we shall omit the syn-thons and indicate only the reagents and reaction conditions. 

Heterocychc A/-oxides can react at the oxygen atom with a variety of electrophilic reagents to give adducts which, according to the reagent and reaction conditions, may be stable or react further (39). Heterocychc A/-oxides are reduced by reaction of nucleophiles at the N-oxide oxygen. 

For all of these reactions, the reagents and reaction conditions must be chosen to meet the fundamental requirement for successful chain reactions. Each step in the sequence must be exothermic to permit chain propagation. ... 

Similarly, Itexafluoroprapylene undergoes fluoride ion induced homotelo-merization to give a series of dimers and trimers These telomerizations can be induced by other nucleophiles, such as amines Indeed, the selectivity of the pi oce-,s can be changed significantly by varying reagents and reaction conditions [25, 26] (equations 19 and 20)... 

Aminofurazans underwent condensation with ketones to form either aminals [86MI2], Schiff bases (74JA7812, 91JHC1677), or fused furazans (86JHC1519), depending on the nature of reagents and reaction conditions (Scheme 120). 

Hydroxy- and 1-alkoxyindoles undergo characteristic reactions depending on their structures, reagents, and reaction conditions. At the beginning of this section, preparations of 1-alkoxyindoles and l-(Q -D-glucopyranosyl)indoles are discussed. 

The lithiation of 2-F- and 3-F-pyridines has been investigated with different reagents and reaction conditions. 

Suggest reagents and reaction conditions that would be suitable for effecting each of the following conversions. 

The aldol reaction is also important in the synthesis of more complex molecules and in these cases control of both regiochemistry and stereochemistry is required. In most cases, this is accomplished under conditions of kinetic control. In the sections that follow, we discuss how variations of the basic mechanism and selection of specific reagents and reaction conditions can be used to control product structure and stereochemistry. 

Derivatives with various substituted sulfonamides have been developed and used to form enolates from esters and thioesters.137 An additional feature of this chiral auxiliary is the ability to select for syn or anti products, depending upon choice of reagents and reaction conditions. The reactions proceed through an acyclic TS, and diastereoselectivity is determined by whether the E- or Z-enolate is formed.138 /-Butyl esters give A-enolates and anti adducts, whereas phenylthiol esters give syn adducts.136... 

A crucial issue for these reactions is the stereoselectivity for formation of E- or Z-alkene. This is determined by the mechanisms of the reactions and, as we will see, can be controlled in some cases by the choice of particular reagents and reaction conditions. 

Step-by-step retrosynthetic analysis of each of the target molecules reveals that they can be efficiently prepared in a few steps from the starting material shown on the right. Do a retrosynthetic analysis and suggest reagents and reaction conditions for carrying out the desired synthesis. 

When a multistep synthesis is being undertaken with other sensitive functional groups present in the molecule, milder reagents and reaction conditions may be necessary. As a result, many alternative methods for effecting interconversion of the carboxylic acid derivatives have been developed and some of the most useful reactions are considered... 

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. 

Each of the following transformations was performed advantageously with a thexylborane derivative. Give appropriate reactants, reagents, and reaction conditions for effecting the following syntheses in a one-pot process. 

Indicate appropriate reagents and reaction conditions or a short reaction sequence that could be expected to effect the following transformations ... 

Give reagents and reaction conditions that would accomplish each of the following transformations. Multistep schemes are not necessary. Be sure to choose conditions that would lead to the desired isomer as the major product. 

The focus of Part B is on the closely interrelated topics of reactions and synthesis. In each of the first twelve chapters, we consider a group of related reactions that have been chosen for discussion primarily on the basis of their usefulness in synthesis. For each reaction we present an outline of the mechanism, its regio- and stereochemical characteristics, and information on typical reaction conditions. For the more commonly used reactions, the schemes contain several examples, which may include examples of the reaction in relatively simple molecules and in more complex structures. The goal of these chapters is to develop a fundamental base of knowledge about organic reactions in the context of synthesis. We want to be able to answer questions such as What transformation does a reaction achieve What is the mechanism of the reaction What reagents and reaction conditions are typically used What substances can catalyze the reaction How sensitive is the reaction to other functional groups and the steric environment What factors control the stereoselectivity of the reaction Under what conditions is the reaction enantioselective ... 

Synthesis consists of (1) planning the reaction sequence with respect to the given conditions, (2) executing the optimal reaction path, (3) isolating the product and workup, and (4) improving yield and selectivity of the conversion by changing reagents and reaction conditions. The difference between chemical and electrochemical reactions lies mainly in the set of available reactions for points (1) and (2) and the equipment used in (2). These points will be addressed in Sects. 3.4-3.6. 

The behaviour of vinylic tellurides towards several reagents and reaction conditions used in organic synthesis... 

A systematic study was undertaken to ascertain the behaviour of functionahzed vinylic tellurides, such as those depicted in the following figure towards several reagents and reaction conditions. " ... 

Each of the following transformations can be carried out in good yield under optimized conditions. Consider the special factors in each case, and discuss the most appropriate reagent and reaction conditions to obtain good yields. 

The molecular orbital structure of 1,2,3-benzotriazine has been calculated using the Hiickel method, and the energy levels, charge densities, and wave functions were obtained.Theoretically the charge densities thus obtained should be of some value in predicting the positions of electrophilic and nucleophilic attack, but in the absence of information on reagents and reaction conditions, such predictions cannot be made with any degree of accuracy. 

Acids and Lewis acids react with quinoline at the basic nitrogen atom to form quinolinium salts, and there is a question over the nature of the substrate for electrophilic attack, i.e. is it quinoline or the quinolinium cation The answer is not a simple one and appears to depend upon the reagents and reaction conditions. Thus, whereas acetyl nitrate at 20 °C gives mainly 3-nitroquinoline (Scheme 3.2), fuming nitric acid in concentrated sulfuric acid containing sulfur trioxide at 15-20 °C yields a mixture of 5-nitroquinoline (35%) and 8-nitroquinoline (43%) (Scheme 3.3). In the case of acetyl nitrate, the reaction may proceed by the 1,4-addition of the reagent to quinoline, followed by electrophilic attack upon the 1,4-dihydro derivative. 

Thieno[2,3-. ]pyridines, 115, form via a condensation reaction with halogenated carbonyl compounds, as shown in Scheme 35. Depending on the base strength of the reagent and reaction conditions, intermediate 114 may be isolated <2005CCA63>. 

Reduction One or both rings of naphthalene can be reduced partially or completely, depending upon the reagents and reaction conditions. 

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