Organic chemistry transformations

Whereas several areas of biocatalysis - in particular the use of easy-to-use hydrolases, such as proteases, esterases and lipases - are sufficiently well research to be applied in every standard laboratory, other types of enzymes are still waiting to be discovered with respect to their applicability in organic-chemistry transformations on a preparative scale. This latter point is stressed in this volume, which concentrates on the newcomer-enzymes which show great synthetic potential. 

Condensation reactions are widely used in solid-phase organic chemistry. Transformations proceed cleanly and in high yield. Traditional Claisen, Knoevenagel, imine, Man-nich, enamine and other condensation reactions are summarized in the next tables. 

Several other basic chiral building blocks can be derived by simple organic chemistry transformations of these PHB derivatives. For example, (/ )-l-chloro-3-butanol (4) may be obtained from the glycol 3a via the tosyl derivative (3b) by nucleophilic substitution with lithium chloride. The product can then be subjected to sequential metallation with butyllithium and then lithium naphthalide in THF at -78°C to give stable solutions of the highly reactive C-metallated... 

The reactive intermediates common in organic chemistry transformations. 

Acids and bases are catalysts, reactants, products, and intermediates in many organic chemistry transformations. When writing mechanisms for reactions involving acids and bases, there are three general rules that will guide you in depicting the correct... 

In investigations on automated solid-phase organic chemistry, transformations involving the use of the highly reactive reagent triphosgene have been conducted using the ACT Model 496 MOS [324]. In particular, applications to the parallel synthesis of a variety of urea and urethane derivatives, primarily derived from amino acid precursors, have been developed. 

The heuristics-aided quantum chemistry (HAQC) methodology of Rappoport et al. (2014) shows many similarities to those previously mentioned, and it has been used for the generation of detailed reaction mechanisms of organic chemistry transformations. 

Chemistry as it was realized substantially derives from the interae-tion of electrons. The electronic theory of chemistry, particularly of organic chemistry, emerged, explaining the great richness of chemical observations and transformation, as expressed by Ingold, Robinson, Hammett, and many others following in their footsteps. 

Thionyl chloride and phosphorus tribromide are specialized reagents used to bring about particular functional group transformations For this reason we won t present the mechanisms by which they convert alcohols to alkyl halides but instead will limit our selves to those mechanisms that have broad applicability and enhance our knowledge of fundamental principles In those instances you will find that a mechanistic understand mg IS of great help m organizing the reaction types of organic chemistry... 

Functional group transformations of epoxides rank among the fundamental reactions of organic chemistry and epoxides are commonplace natural products The female gypsy moth for example attracts the male by emittmg an epoxide known as disparlure On detechng the presence of this pheromone the male follows the scent to its ongm and mates with the female... 

Section 8 1 Nucleophilic substitution is an important reaction type m synthetic organic chemistry because it is one of the mam methods for functional group transformations Examples of synthetically useful nucleophilic sub stitutions were given m Table 8 1 It is a good idea to return to that table and review its entries now that the details of nucleophilic substitution have been covered... 

An ability to form carbon-carbon bonds is fundamental to organic synthesis The addition of Grignard reagents to aldehydes and ketones is one of the most frequently used reactions m synthetic organic chemistry Not only does it permit the extension of carbon chains but because the product is an alcohol a wide variety of subsequent func tional group transformations is possible... 

Enamines are used as reagents in synthetic organic chemistry and are involved in cer tain biochemical transformations... 

We 11 see numerous examples of both reaction types m the following sections Keep m mind that m vivo reactions (reactions m living systems) are enzyme catalyzed and occur at far greater rates than those for the same transformations carried out m vitro ( m glass ) m the absence of enzymes In spite of the rapidity with which enzyme catalyzed reactions take place the nature of these transformations is essentially the same as the fundamental processes of organic chemistry described throughout this text... 

Addition Reactions. The addition of nucleophiles to quinones is often an acid-catalyzed, Michael-type reductive process (7,43,44). The addition of benzenethiol to 1,4-benzoquinone (2) was studied by A. Michael for a better understanding of valence in organic chemistry (45). The presence of the reduced product thiophenyUiydroquinone (52), the cross-oxidation product 2-thiophenyl-1,4-benzoquinone [18232-03-6] (53), and multiple-addition products such as 2,5-(bis(thiophenyl)-l,4-benzoquinone [17058-53-6] (54) and 2,6-bis(thiophenyl)-l,4-benzoquinone [121194-11-4] (55), is typical ofmany such transformations. 

One of the frmdamental structural facets of organic chemistry, which has been explained most satisfactorily in MO terms, is the existence of a small barrier to rotation about single bonds. In ethane, for example, it is known that the staggered conformation is about 3kcal/mol more stable than the ecl sed conformation so that the eclipsed conformation represents a transition state for transformation of one staggered conformation into another by rotation. 

Up to this point, we have emphasized the stereochemical properties of molecules as objects, without concern for processes which affect the molecular shape. The term dynamic stereochemistry applies to die topology of processes which effect a structural change. The cases that are most important in organic chemistry are chemical reactions, conformational changes, and noncovalent complex formation. In order to understand the stereochemical aspects of a dynamic process, it is essential not only that the stereochemical relationship between starting and product states be established, but also that the spatial features of proposed intermediates and transition states must account for the observed stereochemical transformations. 

In the first century of "organic" chemistry much attention was given to the structures of carbogens and their transformations. Reactions were classified according to the types of substrates that underwent the chemical change (for example "aromatic substitution," "carbonyl addition," "halide displacement," "ester condensation"). Chemistry was taught and learned as transformations characteristic of a structural class (e.g. phenol, aldehyde) or structural subunit... 

The structure, and the mechanism of the chemical transformations, of the pseudo ammonium bases which can be obtained from heterocyclic quaternary ammonium salts has been one of the most discussed phenomena in theoretical organic chemistry since the first publication in this field by Claus and Himmelmann. These questions have still not been finally decided. 

Today, we refer to the transformations taking place in Walden s cycle as nucleophilic substitution reactions because each step involves the substitution of one nucleophile (chloride ion, Cl-, or hydroxide ion, HO-) by another. Nucleophilic substitution reactions are one of the most common and versatile reaction types in organic chemistry. 

Alcohols occupy a central position in organic chemistry. They can be prepared from many other kinds of compounds (alkenes.. alkyl halides, ketones, esters, and aldehydes, among others), and they can be transformed into an equally wide assortment of compounds (Figure 17.3). 

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Tandem reaction strategies can accomplish several synthetic objectives in a single step.6 The rapidity with which they can build up molecular complexity is a most useful and impressive virtue. For example, cation-induced, biomimetic polyolefinic cyclizations7 are among the most productive and atom-economical8 single-step transformations known in organic chemistry. In one of the most spectac-... 

The term dediazoniation was introduced by Bunnett as early as 1954. It is now included in the IUPAC system of naming transformations in organic chemistry (IUPAC, 1989 a). 

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