Synthesis of Aromatic Compounds

A SUMMARY OF REACTIONS AVAILABLE FOR USE IN THE SYNTHESIS OF AROMATIC COMPOUNDS. 

The first examples illustrate that the order of addition of the substituents is important in controlling their orientation. For example, suppose we needed to prepare m-chloronitrobenzene from benzene. Because the chlorine is an ortho/para director and the nitro group is a meta director, it is apparent that the nitro group must be added first if the meta product is desired  

On the other hand, if the para-isomer is desired, then the chlorine must be substituted onto the ring first  

These examples show that a synthesis must be carefully planned. The regiochemistry of each step must be considered as well as the compatibility of the substituents already on the ring with the reaction conditions. However, when completed, a cleverly crafted synthesis is a thing of beauty Chemists often describe such a synthesis as elegant. 

Show syntheses of these compounds from benzene  

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KREUZALER, F., HAHLBROCK, F., Enzymatic synthesis of aromatic compounds in higher plants. Formation of fe-noryangonin (4-hydroxy-6[4-hydroxystyryl]2-pyrone) from p-coumaroyl-CoA and malonyl-CoA, Arch. Biochem. Biophys., 1975, 169, 84-90. 

Boronic acid hnkers (Tab. 3.6) are useful for the attachment of diols, the protection of glycosides [105] or as precursors for the metal-mediated cleavage [106]. The boronates formed are sensitive to water and simple hydrolysis is sufficient for cleavage. Recently, Carreaux and Carboni developed a new boronate-based strategy for traceless sohd-phase synthesis of aromatic compounds [107]. 

Kreuzaler F, Hahlbrock K (1972) Enzymatic synthesis of aromatic compounds in higher plants formation of naringenin (5,7,4 -trihydroxyflavanone) from p-coumaroyl coenzyme A and malonyl coenzyme A. FEBS Lett 28(l) 69-72... 

Importance of Diazonium Salts in Synthesis of Aromatic Compounds 398... 

Deoxy-D-araZu o-heptulosonate-7-phosphate synthetase (DAHPS) is the initial enzyme in the pathway responsible for the synthesis of aromatic compounds in microorganisms and plants. It catalyses the reaction shown in Equation (4) ... 

The reagent has been used for synthesis of aromatic compounds. Example ... 

Primary aromatic amines react with nitrous acid to give aryldiazonium ions, ArN2+, which are useful intermediates in synthesis of aromatic compounds. The process by which they are formed is called diazotization. The nitrogen in these ions can readily be replaced by various nucleophiles (OH, Cl, Br, I, CN). Diazonium ions couple with reactive aromatics, such as amines or phenols, to form azo compounds, which are useful as dyes. 

Basic Principles Synthons and Reagents Synthesis of Aromatic Compounds... 

Alternating with instructional chapters, like the last one, will be strategy chapters, like this one, which discuss reasons for choosing one route rather than another in other words the overall plan rather than the individual steps. In this chapter we shall examine the order of events, using the synthesis of aromatic compounds as examples. The details are specific but the guidelines general. 

Fig. 16.23. Suzuki coupling for the synthesis of aromatic compounds with a functionalized side chain.

This section presents several additional reactions that are very useful in the synthesis of aromatic compounds because they provide methods to convert substituents that can be attached by electrophilic substitution reactions to other substituents that cannot be attached directly. The mechanisms of these reactions need not concern us here. 

The Heck reaction was discovered independently in the end of 1960s by T. Mizoroki and R. F. Heck . But Heck developed it into a synthetically useful reaction. Since then it has become one of the most important reactions for the synthesis ° of aromatic compounds substituted with alkenes. 

Transition metal complexes are widely used in aromatic chemistry and organic synthesis in general. They are of particular value because com-plexation of an organic molecule to a metal centre often modifies its reactivity. The metal can subsequently be removed. After discussing the ways by which these complexes react, we will discuss their use in the synthesis of aromatic compounds. 

The first chapter discusses the concept of aromaticity, after which there is a description of aromatic substitution reactions. Chapters covering the chemistry of the major functionalized derivatives of benzene follow. A chapter on the use of metals in aromatic chemistry discusses not only the chemistry of Grignard reagents and aryllithium compounds but also the more recent uses of transition metals in the synthesis of aromatic compounds. The penultimate chapter discusses the oxidation and reduction of the benzene ring and the text concludes with the chemistry of some polycyclic compounds. 

The dehydrogenation of hexane to hexene or cyclohexane (reactions 5 and 6) only becomes appreciable at temperatures approaching 800 °K. The dehydrogenation to methylcyclopentane however appears to be thermodynamically feasible at temperatures as low as 350 °K. One cannot place too much reliance on this particular result since the affinity of formation of methylcyclopentane is known less accurately than the others. These three reactions, however, scarcely affect the synthesis of aromatic compounds in the reaction since the ethylenes and cycloparaffins are thermodynamically unstable relative to aromatic hydrocarbons above 550 °K, and they decompose spontaneously to form aromatics at this temperature. They can therefore only appear as intermediates in reaction (9) above 550 °K. 

Diels-AUer reactions. Hill and Carlson showed that reaction of the reagent with dienophiles in refluxing benzene or without solvent at 100-110 provides a useful one-step synthesis of aromatic compounds. An example other than that formulated... 

A new germanium-based hnker has been developed for solid-phase synthesis of aromatic compounds. Cleavage from the polymer support via ipso-degerrnylalion with TFA, Id, Bry, and NCS provides protio, bromo, and chloroaryl compounds, respectively (Scheme 11.55) [78]. 

Addition to coordinated arenes is a reliable method for achieving overall aromatic nucleophilic substitution with formal displacement of hydride [17]. This method illustrates the use of nucleophilic addition to an arenetricarbonyl-chromium for the synthesis of aromatic compounds with unusual substitution patterns. 

The intramolecular Diels-Alder (IMDA) cycloadditions <05CR4779 02AC(E)1668> of 2-pyrones have not been exhaustively explored, due to the lack of synthetic methods to incorporate requisite tethered dienophiles. Only a few examples can be found in the literature and they have been employed mostly in the synthesis of aromatic compounds. 

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