Objectives of Organic Synthesis

Roald Hoffmann, a former coworker of R.B. Woodward and Nobel Prize as well for his contribution to the frontier orbital theory (the famous Woodward-Hoffmann rules concerning the conservation of molecular orbital symmetry), has also emphasised the artistic aspects of organic synthesis "The making of molecules puts chemistry very close to the arts. We create the objects that we or others then study or appreciate. That s exactly what writers, visual artists and composers do" [15a]. Nevertheless, Hoffmann also recognises the logic content of synthesis that "has inspired people to write computer programs to emulate the mind of a synthetic chemist, to suggest new syntheses". 

Recently, the power of designer acid catalysts has generally increased as a result of the development of the catalytic enantioselective versions described here. In particular, combined acid catalysis is still very much in a state of infancy, and there is still much more to learn with regard to new reactivity. The ultimate goal is a more reactive, more selective, and more versatile catalyst. We beheve that the realization of such an objective would be a tremendous benefit for the further development of organic synthesis, including green chemistry. 

Novel vinyl liquid crystalline (l.c.) polymers were synthesized with the UV-sensitive p-methoxycinnamate chromophore incorporated into the side chain of the polymers. The objective of this synthesis was to determine if a molecularly organized environment could influence the yield of a chemical reaction in the solid state. The investigation into the photochemical and physical processes of these thin films revealed that the photodimerization of the p-methoxycinnamate moieties was very sensitive to their geometrical arrangement in the polymer matrix. The relative quantum yield of cyclobutane formation increased by a factor of approximately 8 for the l.c. p-methoxycinnamate film compared to its amorphous analog. This quantum yield approaches the theoretical limit for this system. 

Sometimes it is possible to find experimental conditions which satisfy all the specified criteria sometimes there are conflicts between certain criteria and a compromise solution must be found. It is evident that such problems can be difficult to solve. A special branch of mathematics, "Optimization theory" is devoted to this type of problem. In this area it is assumed that the object function (the "theoretical" response function) is perfectly known, and that the final solution can be reached by using mathematical and numerical methods. [17] From the discussions in Chapter 3, it is evident that mathematical optimization theory is difficult to apply in the area of organic synthesis, especially when new ideas are explored. Conclusions must be drawn from observations in suitably designed experiments. The response surface models thus obtained are local and approximate, and definitefy not perfectly known. Nevertheless, we shall see that we can use experimentally determined models to find solutions to the problems sketched above. 

Various nucleophiles react with epoxides stereospecifically to give 1,2-difunc-tionalized products, establishing the stereochemistry of two vicinal carbons accordingly, optically active epoxides serve as useful synthetic intermediates for the construction of wide range of enantiopure compounds. Thus, the synthesis of optically active epoxides is the very important objective in organic synthesis... 

Control of selectivity (chemo, regio, stereo, and enantioselectivity) is among the most important objective in organic synthesis. The efficient use of reaction conditions (temperature, time, solvent, etc.), kinetic or thermodynamic control, protecting or activating groups (for example chiral auxiliaries), and catalysts (including chiral catalysts) have all been used to obtain the desired isomer. 

The objective of this book is to focus on the different fields of application of this technology in several aspects of organic synthesis. This second edition is a revised and enlarged version of the first. Eight new fields of application have been included. The chapters, which complement each other, are written by the most eminent scientists, all well-recognized in their fields. 

Synthesis is generally the most important objective of organic chemists, applicable to the preparation of compounds for use as pharmaceuticals, agrochemicals, plastics, elastomers, and textile fibers. A successful synthesis must provide the desired product in a maximum yield with a maximum control of stereochemistry at all stages of the synthesis. Furthermore, there is an increasing desire to develop "green" syntheses (i.e., syntheses that do not produce or release by-products harmful to the environment). 

One of the main objectives of organic and medicinal chemistry is the design, synthesis, and production of molecules having value as human therapeutic agents. Rhodanine scaffold is a powerful tool for the medicinal chemist and has a broad substrate scope for the synthesis of various heterocyclic moieties (Scheme 9.5) with a wide range of pharmacological activities, such as antimalarial, antimicrobial, antiviral, antidiabetic, and anticonvrrlsant effects [18]. 

The first of our panel discussions dealt with the total synthesis of natural products, and the second with the relation of organic synthesis to the life sciences. The panelists for the third and last discussion. Professors Lehn [Louis Pasteur University, Strasbourg], Reinhoudt [University of Twente], and Whitesides [Harvard University], with Prof. Eschenmoser [ETH Zurich] lurking in the background, will consider an even more complex subject, the synthesis of large objects composed of molecular modules. 

Recently, C-H activation catalyzed by transition metals has been recognized as a challenging objective in organic synthesis. In 2011, Takai and coworkers established the first example of a Pd(0)-catalyzed C-H phosphorylation reaction in an... 

The ultimate goal is to apparently develop a more reactive, more selective, and more versatile catalyst. We believe that the realization of such an objective would be a tremendous beneht for the development of organic synthesis including green chemistry. 

Indole and isoquinolone nuclei are prominent structural units frequently found in numerous natural products and pharmaceutically active compounds. Thus, the search for new methodologies to obtain these scaffolds with different substitution patterns is a current major objective in organic synthesis. Similar to benzofuran synthesis, Aluraez et al. observed that the palladium-catalyzed cascade intramolecular alkyne aminopaUadation/intermolecular Heck-type coupling reaction under oxidative conditions is an efficient methodology for the synthesis of indole 217 and isoquinolone 219 derivatives, starting from readily available aniline 216 or benzamide 218 substrates and functional alkenes [77] (Scheme 6.60). 

A challenging task in material science as well as in pharmaceutical research is to custom tailor a compound s properties. George S. Hammond stated that the most fundamental and lasting objective of synthesis is not production of new compounds, but production of properties (Norris Award Lecture, 1968). The molecular structure of an organic or inorganic compound determines its properties. Nevertheless, methods for the direct prediction of a compound s properties based on its molecular structure are usually not available (Figure 8-1). Therefore, the establishment of Quantitative Structure-Property Relationships (QSPRs) and Quantitative Structure-Activity Relationships (QSARs) uses an indirect approach in order to tackle this problem. In the first step, numerical descriptors encoding information about the molecular structure are calculated for a set of compounds. Secondly, statistical and artificial neural network models are used to predict the property or activity of interest based on these descriptors or a suitable subset. 

When esterification is the objective water is removed from the reaction mixture to encourage ester formation When ester hydrolysis is the objective the reaction is carried out m the presence of a generous excess of water Both reactions illustrate the applica tion of Le Chatelier s principle (Section 6 10) to organic synthesis... 

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