Reduction of arene

The use of reducing metals nowadays is mainly restricted to acyloin and pinacol coupling reactions (see p. 53f.) and Birch reductions of arenes (A.A. Akhrcm, 1972 see p. 103f.) and activated C—C multiple bonds (see p. 103f.). 

Reduction of arenes by catalytic hydrogenation was described m Section 114 A dif ferent method using Group I metals as reducing agents which gives 1 4 cyclohexadiene derivatives will be presented m Section 1111 Electrophilic aromatic substitution is the most important reaction type exhibited by benzene and its derivatives and constitutes the entire subject matter of Chapter 12... 

Cathodic addition involves either the reduction of a 7T-system in an ECEC process (electrochemical, chemical, electrochemical, chemical) and the chemical reaction (C) of the intermediates with a carbon or heteroatom electrophile or the cathodic conversion of a C—X bond in an ECE process into an anion that adds to an electrophilic jr-system. The electrochemical Birch reduction of arenes... 

Reactions with Protic, ionic, Poiar Reagents. The reactions of radical anions with proton donors include the reduction of arenes, the well-known Birch reduction, as well as alkynes by alkali metals in liquid ammonia. Both reactions have synthetic utility and belong to the few radical ion reactions included in elementary textbooks. 

Reduction of arene-Tr-cyclopentadienyliron(II) cations, which are iso-electronic with the di-ir-cyclopentadienylcobalt cation, with lithium aluminium hydride yields the neutral arenecyclopentadiene-iron complexes (100) ... 

Reduction of arenes.1 Raney nickel (Mozingo type) in combination with 2-propanol (reflux) effects reduction of aromatic rings in 2-18 hours. Naphthalene is reduced in 18 hours to tetralin (90% yield) and cis- and frans-decalin (10% yield). Anisole is reduced in 110 hours to cyclohexyl methyl ether (90% yield). Nitrobenzene is reduced quickly to aniline and then further to cyclohexylamine and cyclohexylisopropylamine. 

Reduction of arenes. A number of phenyl-substituted compounds can be reduced to the corresponding cyclohexyl derivatives by NaBH4 that has been incubated with RhCl3 in ethanol at 0-30°.1 Examples ... 

As early as 1969, Pedersen was intrigued by the intense blue colour observed upon dissolution of small quantities of sodium or potassium metal in coordinating organic solvents in the presence of crown ethers. Indeed, the history of alkali metal (as opposed to metal cation) solution chemistry may be traced back to an 1808 entry in the notebook of Sir Humphry Davy, concerning the blue or bronze colour of potassium-liquid ammonia solutions. This blue colour is attributed to the presence of a solvated form of free electrons. It is also observed upon dissolution of sodium metal in liquid ammonia, and is a useful reagent for dissolving metal reductions , such as the selective reduction of arenes to 1,4-dienes (Birch reduction). Alkali metal solutions in the presence of crown ethers and cryptands in etheric solvents are now used extensively in this context. The full characterisation of these intriguing materials had to wait until 1983, however, when the first X-ray crystal structure of an electride salt (a cation with an electron as the counter anion) was obtained by James L. Dye and... 

The chemical or electrochemical reduction of [(arene)Mn(CO)3]+ (23+) can lead to bimolecular coupling through the arene rings, CO loss followed by dimerization, or arene ring slippage.134 Which mode of decomposition is followed depends on many factors, especially the nature of the arene. In the presence of P(OBu)3, these decomposition pathways are short circuited in favor of ETC substitution to give [(arene)Mn(CO)2P(OBu)3]+. For example, Fig. 6 shows that application of a reducing current for a... 

A special case involves complexes of cyclohexadienyl ligands, which may result from the addition of nucleophiles to r)6-arene complexes (Section 7.7) or hydride abstraction from complexes of readily available cyclohexadienes (Birch reduction of arenes) (Figure 7.14). In the latter case, it is within the chemistry of iron that such complexes find the widest... 

Although not a catalytic reaction, the reduction of arenes with electropositive metals like lithium, zinc or aluminium in chloroaluminate... 

Reduction of arenes. Calcium in combination with amines, generally methylamine or ethylenediamine, reduces aromatic hydrocarbons to monoenes in generally high yield.1 Addition of r-butyl alcohol to this system effects reduction to nonconjugated dienes (Birch-type products). Ethylenediamine is essential in this case addition of a second amine is generally desirable for solubility reasons.2... 

In this section, the -ligands obtained from the reduction of arene rings will be described. 

The partial reduction of arenes can be achieved using the Birch reduction An alkali metal (lithium, sodium or potassium) is dissolved in liquid ammonia in the presence of the arene, an alcohol, such as 2-methylpropan-2-ol tert-buty alcohol) and a co-solvent to assist solubility. 

Reduction of arene cyclopentadienyl iron cations was another interesting aspect of the research. 

The most general synthetic route to benzene oxides-oxepins is that initially developed by Vogel for 1. 1,4-cyclohexadienes (readily available from [2+4] cycloaddition of alkynes and butadienes, lithium-ammonia reduction of arenes, or dehydration of cyclohexenols) were converted to dibromoepoxides, the immediate precursors of benzene oxides. Modifications of this route have been used to prepare Ic and Id. Treatment of the monosubstituted arene oxide 43 (Figure 3) with (Et)4NF or thermal isomerization of 3-oxaquadricyclane provide additional synthetic routes to la. Similarly, the thermal (or photochemical) isomerization of the monoepoxide of Dewar benzene yielded la. ... 

Aromatic amines are found in biologically active natural products, common pharmaceuticals, dyestuffs, materials with conductive and emissive properties, and ligands for transition-metal-catalyzed reactions. For these reasons much effort has been spent for more than a century on methods to prepare aromatic amines. The synthetic methods to obtain these materials range from classical methods, such as nitration and reduction of arenes, direct displacement of the halogens in haloarenes at high temperatures, or copper-mediated chemistry, as well as modem transition-metal-catalyzed processes and improved copper-catalyzed processes. The following sections describe each of these synthetic routes to aromatic amines, including information on the scope and mechanism of most of these routes to anilines and aniline derivatives. 

Reduction of arenes by A1 in ionic liquids is efficient. For example, pyrene is fully saturated (84% yield) and 9,10-dimethylanthracene gives the 9,10-dihydro derivative (81%). ... 

Reduction of arenes (1, 228). A mechanism involving free-radical intermediates has been proposed. ... 

Reductions for which group 1 metals are used in organic chemistry can be divided into two broad classes those that involve addition of H2 across a tt bond, and those in which a bonds between non-H atoms are formed or broken. The conjugate reduction of a,j3-unsaturated ketones, the reduction of alkynes to trans-alkenes, and the Birch reduction of arenes belong to the first class. The reduction of C—X bonds, C—O bonds a to a carbonyl, and acyloin and pinacol condensations belong to the second class. 

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