FROM ARENES

The Birch reduction not only provides a method to prepare dienes from arenes which cannot be accomplished by catalytic hydrogenation but also gives a nonconju gated diene system rather than the more stable conjugated one... 

Bis-arene iron dications [20] are easily accessible from arenes, A1C13 and FeCl3 (for C6Me6, FeCl2 must be used). It is advisable to use tris-sublimated A1C13 to avoid problems of isomerization [23], With toluene, this isomerization due to the re/ro-Friedel-Crafts mechanism [24] is too extensive to give any clean complex. 

The complexes precipitate immediately on mixing 1 1 complexes (n = 1) are prepared from arenes such as benzene, biphenyl, naphthalene, acenaphthalene, fluorene, phenanthrene, anthracene and m-dinitrobenzene. These complexes contain a complex Hg(I) cation with the arene v coordinated to one Hg as in III ... 

Carless HAJ, Billinge JR, Oak OZ (1989) Photochemical routes from arenes to inositol intermediates the photo-oxidation of substituted cw-cyclohexane-3,5-diene-l,2-diols. Tetrahedron Lett 30 3113-3116. 

Organometallic complexes of copper, nickel, and palladium have been used in indole syntheses from arenes. Most of the reactions proceed under relatively mild conditions and in some cases give rise to formation of the less common 2-substituted compounds.68 Good yields of such 2-substituted derivatives are formed in reactions of o-iodoarylamines with cuprous acetylides in dimethylformamide (Scheme 41 ).69 The efficiency of this type of... 

These are the same quinones that are formed when 6-hydroxy-BP is oxidized by air or microsomes (19). However, there is no definitive evidence that 6-hydroxy-BP is an intermediate in their formation by PGH synthase. Among all of the stable metabolites of BP, the quinones are distinctive because, unlike phenols and dihydrodiols, they are not derived from arene oxides. Thus, arene oxides do not appear to be products of BP oxidation by PGH synthase (19,20). 

Two other polycyclic hydrocarbons, 3-methylcholanthrene and 7,12-dimethylbenzanthracene are oxidized during arachidonate metabolism (21,26). Hydroxymethyl compounds that do not arise from arene oxides appear to be the products formed from 7,12-dimethylbenzanthracene. ... 

Iridium-catalyzed formation of B-C bonds from arene C-H bonds was first reported by Smith and coworkers [73]. They demonstrated that the archetypal C-H activation products, Cp lr(PMe3)(H)(R), could mediate B-C bond formation (R = Ph, cyclohexyl) and were able to effect the catalytic borylation of benzene with HBpin (8) to produce CgHsBpin and H2 at 150°C (8). 

At the time of the earlier review (66HC1155), it was already known that combinations of arenes with sulfur, or with sulfur mono- or dichlorides in the presence of Lewis acids (IV,B,1), or of aryl thiols, diaryl sulfides, or disulfides (IV,B,2 and 3) again heated with Lewis acid catalysts, generate thianthrenes, sometimes in acceptable preparative yields. A complimentary method is the treatment of aryl thiols with c. H2SO4. Routes from arenes and aryl thiols almost certainly involve the initial formation of diaryl sulfides. All these methods inevitably give symmetrical thianthrenes carrying identical substituents on each benzene ring (Scheme 9), unless the second sulfur is introduced in a controlled fashion into a preformed, unsymmetrical diphenyl sulfide. 

The synthesis of 1,4-dithiines from arenes and heteroarenes has been known for more than 100 years. The reaction of quinoline and sulfur monochloride gave dithiodiquinoline 152 (R = R = H) (1896JPR340). The structure of such compounds has been correctly identified only recently (1976PJC785, 1997JCR(S)435 Scheme 80). 

RADICAL IONS FROM ARENES BIRCH REDUCTION AND ARENE OXIDATION... 

Early examples of electron transfer processes are shown in equations (2), (12), and (13). Birch in 1944 followed up the findings of Wooster, and demonstrated that Na metal and ethanol in ammonia reduce benzene, anisole, and other aromatics to 1,4-cyclohexadienes. Birch speculated about the mechanism of this reaction, but did not explicitly describe a radical pathway involving 55 (equation 87) until later, as described in his autobiography. Electron transfer from arenes was found by Weiss in 1941, who obtained crystalline salts of Ci4H]o from oxidation of anthracene. ... 

Crafts alkylation and acylation (Section 22-4E and 22-4F), the Gattermann-Koch reaction for preparation of aldehydes from arenes and carbon monoxide (Section 22-4F), and the Kolbe-Schmitt, Reimer-Tiemann, and Gattermann reactions for synthesis of acids and aldehydes from arenols (Section 26-1E). 

The smooth replacement of a heteroatom (usually halide) from arene ligands requires reversible addition of the nucleophile, since the kinetic site of addition is usually at a position bearing a hydrogen substituent (Scheme 3, path it]). 

A stereospecific synthesis of aziridine 266 has been reported by Ittah et al. from arene oxide 1 by treatment with sodium azide, followed by tri-phenylphosphine reaction. The reaction proceeds via a phosphonium hydroxide intermediate (267).157... 

What is remarkable, however, is the stereochemical influence of a 13-hydroxyl group, p-hydroxycarbocations such as 31 are formed not only from arene oxide as precursors but from arene dihydrodiols. As shown for the parent benzene dihydrodiols in Scheme 23, arene dihydrodiols exist as cis-and /ra/rv-isomers. The m-isomers are obtained as products of the action on the aromatic molecule of dioxygenase enzymes and have been prepared on a large scale by fermentation.92 The trans-isomers are normally accessible by straightforward synthesis, for example, from the arene oxide. Both isomers undergo acid-catalyzed dehydration to the parent aromatic molecule, as is also shown in Scheme 23. It is clear that their reactions should involve a common carbocation intermediate,163 164 and in so far as there is little difference in the stabilities of the isomers,165 their difference in reactivities might have been expected to be small. 

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