Classical Organic Reactions

Many classical organic reactions can now be performed with exceptional selectivities and efficiencies when using such catalysts or reagents. 

For example the coupling reactions of aryl halides, classically based on copper metal catalysis (Ullmann coupling), can now be advantageously realized when using Ni(0) or Pd(0) reagents, transient aryl metal derivatives being formed as reactive intermediates. 

Similarly, the coupling reactions of allyl systems in intermolecular or intramolecular (cyclization) ways is also best performed with nickel(O) reagents (a Corey reaction) [2]. 

4-addition reactions of nucleophiles onto a, / -unsaturated ketones are well-known in Michael-type processes such reactions are run with high regioselectivities when using organocuprate reagents. 

Even the classical malonic synthesis and other related nucleophilic substitution reactions based on stabilized carbanions proceeds very smoothly when using r-allyl palladium complexes as the electrophilic partner. 

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Examples of commercially applied solid base catalysts are much fewer than for solid acids. Nevertheless, much attention is currently focused on the development of novel solid base catalysts for classical organic reactions such as aldol condensations, Michael additions, and Knoevenagel condensations, to name but a few. 

Reaction Rates Faster than Expected Modem calcnlational methods have made it convenient and rontine to estimate transition state barriers very accurately. It is easy to predict a reasonable approximate rate for a classical organic reaction. However, QMT permits reactions to occur at rates that can be considerably higher than predicted by calculation or by extrapolation from rates measured at room temperature with rapid spectroscopic methods. 

Kuhlmann, B., Arnett, E.M., Siskin, M. 1994. Classical organic reactions in pure superheated... 

Classical Organic Reactions in Pure Superheated Water... 

Classical organic reactions that have been carried out in water include, among others, the Diels-Alder reaction, the Claisen rearrangement, aldol condensations, Michael additions, and nucleophilic substitutions. In the Diels-Alder reaction, for example, water has been found to increase the reaction rate and to enhance the endoselectivity 120). Two reviews summarize the results for organic reactions in water 121). 

There are indeed significant fundamental and practical differences between classical organic reactions (either stoichiometric or homogeneously catalysed ones) and those catalysed by solids and especially zeolites (Table 2.1). It is also the case when one compares the relatively simple transformations generally studied by the specialists in Heterogeneous Catalysis and the transformation of complex molecules involved in the synthesis of Fine Chemicals. The operating conditions are very different high temperature, gas phase, fixed bed reactors on the one hand low... 

Another series of publications from Ken s group compared kinetic isotope effects, computed for different possible transition structures for a variety of reactions, with the experimental values, either obtained from the literature or measured by Singleton s group at Texas A M. These comparisons established the most important features of the transition states for several classic organic reactions — Diels-Alder cycloadditions, Cope and Claisen rearrangements, peracid epoxidations, carbene and triazolinedione cycloadditions and, most recently, osmium tetroxide bis-hydroxylations. Due to Ken s research, the three-dimensional structures of many transition states have become nearly as well-understood as the structures of stable molecules. 

As has been shown, large-seale synthesis of the poly(propylene imine) dendrimers is possible, and leads to well-characterized products. Both the nitrile and amine groups at the periphery of the poly(propylene imine) dendrimers lend themselves for modification via classical organic reactions nitriles can be converted to carboxylic acids, and amines can be changed to amides, ureas, imines, etc. (Figure 6). Also, other amines can be used as the core molecule. 

Extensive problem sets are found at the end of all chapters. The only way you will learn to draw reaction mechanisms is to work the problems If you do not work problems, you will not learn the material. The problems vary in difficulty from relatively easy to very difficult. Many of the reactions covered in the problem sets are classical organic reactions, including many name reactions. All examples are taken from the literature. Additional problems may be found in other textbooks. Ask your librarian, or consult some of the books discussed below. 

This chapter is organized as follows. In Section 2, the basic definitions of the DFT descriptors are reminded, and the master equations that allow defining the new index are presented. The formal relation between the new index and the PMH is also discussed in Section 2. Section 3 deals with the computational details of the theoretical calculations presented and discussed in Section 4 where some classical organic reactions are studied in the light of the new reactivity-selectivity descriptor. Section 5 contains some concluding remarks. 

In this chapter, we have reviewed the usefulness of the global and local electrophilicity indexes to quantitatively account for the reactivity and selectivity patterns observed in a large series of classical organic reactions. The global electrophilicity index, w, categorizes within an unique absolute scale the propensity of the electron acceptors to acquire additional electronic charge from the environment. This classification allowed an impressive number of systems in DA reactions to be rationalized in terms of their reaction mechanisms in polar and nonpolar processes. The global electrophilicity scale provides a simple way to assess the more or less polar character of a process on the... 

In its manifold ventures, chemistry wears many characteristic dresses. Complexity is but one. Variety is another. P. B. Venuto and P. S. Landis survey many classic organic reactions in the presence of a modern class of catalysts acidic solids derived from crystalline aluminosilicates. 

One unique aspect of the carbenoid C-H insertion chemistry is its ability to form products that are typically obtained from more classical organic reactions. One example is the allylic insertion into silyl enol ethers 102 to form products equivalent to those from an asymmetric Michael reaction (Scheme 22) [92], Cyclic substrates provided the desired Michael adducts 103 in the highest ee values for the major isomer (89-96%), but with only moderate de, favoring the diastereomer shown about 1.5 1 to 3 1. The diastereoselectivity was markedly improved to >90% de with acyclic substrate 104 with sterically differentiated substituents, but the enantioselectivity dropped to below 85% ee. Notably, this transformation was limited to aryldiazoacetates. When EDA was utilized as the carbene precursor, cyclo-propanation of the olefin was the major reaction pathway, and only small amounts of the desired C-H insertion were observed. 

The basic oleochemical chemicals, fatty acids, esters, and alcohols, are so far almost exclusively derived via classical organic reactions at the carboxylate or alcohol... 

Use a purely chemical strategy with classical organic reactions and/or new special reactions. 

Addition of a 1,3-dipole to an alkene to give a five-membered ring is a classical organic reaction. Indeed, 1,3-dipolar cycloaddition reactions are useful for formation of carbon-carbon bonds and for preparation of heterocyclic compounds. 

The classical organic reaction for the synthesis of THMs, the so-called haloform reaction, is actually a series of reactions of enolizable compounds whose rate is usually determined by the rate of enolization of a precursor molecule. It is outlined in Figure 5.5. 

An acid or a base can be described as hard or soft and at the same time as strong or weak. Both characteristics must be considered to rationalize reactivity. For example, if the reactivity of two bases with similar softness is being compared, consideration of which base is stronger (from a Br0nsted-Lowry perspective) can be helpful to assess which side of an equilibrium will be favored. For example, consider this classic organic reaction for the synthesis of phenyllithium. 

The well-defined surface functionalization using classical organic reactions plays an important role in membrane development. In order to be susceptible to reaction, the polymer chain should contain double bonds, hydroxyl groups or benzene rings. An example is the modification of polysulfone by reaction with different chemicals to increase hydrophilicity. The surface modification of polysulfone membranes has been reported by several authors [120, 121]. 

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