Aromatic compounds synthetic applications

Aromatic nitro compounds undergo nucleophilic aromatic substitutions with various nucleophiles. In 1991 Terrier s book covered (1) SNAr reactions, mechanistic aspects (2) structure and reactivity of anionic o-complexes (3) synthetic aspects of intermolecular SNAr substitutions (4) intramolecular SNAr reactions (5) vicarious nucleophilic substitutions of hydrogen (VNS) (6) nucleophilic aromatic photo-substitutions and (7) radical nucleophilic aromatic substitutions. This chapter describes the recent development in synthetic application of SNAr and especially VNS. The environmentally friendly chemical processes are highly required in modem chemical industry. VNS reaction is an ideal process to introduce functional groups into aromatic rings because hydrogen can be substituted by nucleophiles without the need of metal catalysts. 

A bond between carbon and halogen can be cleaved quite easily with light221 One of the few synthetic applications of this reaction is the photo-arylation of aromatic compounds, a sequence employed in the synthesis of alkaloids222,223) as shown for the key step in the synthesis of boldine (2.13) 223>. 

Abstract The basic principles of the oxidative carbonylation reaction together with its synthetic applications are reviewed. In the first section, an overview of oxidative carbonylation is presented, and the general mechanisms followed by different substrates (alkenes, dienes, allenes, alkynes, ketones, ketenes, aromatic hydrocarbons, aliphatic hydrocarbons, alcohols, phenols, amines) leading to a variety of carbonyl compounds are discussed. The second section is focused on processes catalyzed by Pdl2-based systems, and on their ability to promote different kind of oxidative carbonylations under mild conditions to afford important carbonyl derivatives with high selectivity and efficiency. In particular, the recent developments towards the one-step synthesis of new heterocyclic derivatives are described. 

The successful synthesis of 2-thienyl and substituted 2- and 3-thienyl-acetylenes in yields as high as 60-80% opened a wide variety of synthetic applications. Various addition reactions with carbonyl compounds or epoxides could be carried out with ease. Aliphatic as well as aromatic amine addition reactions, or condensation reactions with hydrazine or hydroxylamine could be easily performed. 

The Birch reduction has been used by several generations of synthetic organic chemists for the conversion of readily available aromatic compounds to alicyclic synthetic intermediates. Birch reductions are carried out with an alkali metal in liquid NH3 solution usually with a co-solvent such as THF and always with an alcohol or related acid to protonate intermediate radical anions or related species. One of the most important applications of the Birch reduction is the conversion of aryl alkyl ethers to l-alkoxycyclohexa-l,4-dienes. These extremely valuable dienol ethers provide cyclohex-3-en-l-ones by mild acid hydrolysis or cyclohex-2-en-l-ones when stronger acids are used (Scheme 1). 

A broad spectrum of chemical reactions can be catalyzed by enzymes Hydrolysis, esterification, isomerization, addition and elimination, alkylation and dealkylation, halogenation and dehalogenation, and oxidation and reduction. The last reactions are catalyzed by redox enzymes, which are classified as oxidoreductases and divided into four categories according to the oxidant they utilize and the reactions they catalyze 1) dehydrogenases (reductases), 2) oxidases, 3) oxygenases (mono- and dioxygenases), and 4) peroxidases. The latter enzymes have received extensive attention in the last years as bio catalysts for synthetic applications. Peroxidases catalyze the oxidation of aromatic compounds, oxidation of heteroatom compounds, epoxidation, and the enantio-selective reduction of racemic hydroperoxides. In this article, a short overview... 

Oxazoline-directed aromatic substitution and addition reactions provide synthetic chemists with powerful tools for the construction of complex aromatic compounds. Since the last authoritative review by Meyers, these technologies have matured and found widespread applications in organic synthesis. While there has been somewhat limited methodological research in this area in the intervening years, one particularly exciting new development is the diastereoselective ortho-metalations directed by chiral oxazolines. Sections 8.3.9.1-8.3.9.3 will discuss these new developments as well as new synthetic applications of these reactions. 

Diketene also is widely employed as a natural and synthetic fiber cross-linking agent, wood preservative and paper-sizing agent. Both it and /3-propiolactone have wide application as chemical intermediates. The synthetic applications of diketene for the synthesis of aromatic, heterocyclic and aliphatic compounds is exceptionally extensive (74ACR265). 

Aromatic compounds are the most widely used and one of the most important classes of petrochemicals. They are still an important constituent of high-octane gasoline, although because of their carcinogenic nature their application will decrease. FCC gasoline contains about 29% aromatics, whereas the aromatic content of reformates is about 63%. They also are excellent solvents and constitute an important component of synthetic rubbers and fibers. 

Synthetic applications of these photocycloadditions to aromatic compounds are sometimes hampered by low chemical yields and poor selectivity in the photoreactions. However, a number of elegant syntheses of tricyclic sesquiterpenes have been hased on intramolecular 1,3-phutocycloadditions ie.g. 3. SI), and these represent a completely new approach to the preparation of such systems. 

The coupling of aryl- and alkenylzinc reagents with various halides has widespread use in the cross-coupling of aromatic rings [101]. The reactions of zinc derivatives of aromatic and heteroaromatic compounds with aryl and heterocyclic halides have wide synthetic applications [103,104],... 

This chapter discusses specific organ systems that contact a variety of substances in the workplace environment (or due to drug abuse and addiction), leading to health hazards. Important organs discussed here include the skin, the respiratory system, the cardiovascular system, the renal system, and the central nervous system (CNS). In the United States and other countries of the world, the application of phenol is on the increase in the manufacture of aromatic compounds, explosives, fertilizers, paints, rubber products, wood preservatives, synthetic resins, drugs and pharmaceutical products, plastics, leather tanning and... 

Among these reactions, the photochemical cycloadditions of C=C bom which can create up to four asymmetric carbons during the photochemical sti are particularly interesting, and numerous synthetic applications of this react have been reported. Advances in the understanding of the origin of asymmefa induction, during addition of alkenes with carbonyl derivatives, cyclic enom and aromatic compounds, will be discussed in detail. 

HRP catalyzes the oxidative dehydrogenation of a wide range of electron-rich aromatic compounds. The result of this radical formation pathway is dimerization and subsequent oligomerization of the substrates [76-78]. Peroxidases have been used to catalyze polymerizations of phenols (e.g. p-cresol and guaiacol) and aromatic amines (e.g. aniline, and o-phenyldiamine) [79, 80]. N- and O-dealkylations are also useful electron transfer reactions catalyzed by peroxidases. These reactions are used in industrial wastewater treatment and may have synthetic applications [81]. 

The majw work to date on synthetic applications of remote functionalization has involved free radical chlorination. The earliest studies involved the direct attachment of aryliodine dichloride units to the steroid substrates, then intramolecular free radical chain chlorination in benzene or chlorobenzene solution (Scheme 14). Yields were only in the 50% region, but fairly good selecdvities were observed compound (6) afforded chiefly the 9-chloro derivative, while compound (7) produced the 14-chloro steroid. The yields and selectivities were considerably improved when it was realized that aromatic solvents promote intermolecular random processes by forming complexes with C1-, and when the radical relay method was developed. 

Reactions which formally involve the oxidation of azides have been reviewed by Boyer. Other oxidations with useful synthetic applications include two which start from nitrogen ylides. Sulfimides (50) derived from electron-deficient aromatic and heterocyclic amines are oxidized to the corresponding nitroso compounds by MCPBA. - This is a very useful method of preparation of some otherwise inaccessible nitroso compounds such as 2-nitrosopyridine and 1-nitrosoisoquinoline. They can be further oxidized, for example by ozone, to the nitro compounds. Phosphimides (51) are oxidized directly by ozone to the nitro compounds, although the nitroso compounds are intermediates. Isocyanates can also be oxidized to the corresponding nitro compounds, by dimediyldioxiraiK (1). ... 

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