Arenes Experimental Procedure

The synthetic procedure described is based on that reported earlier for the synthesis on a smaller scale of anthracene, benz[a]anthracene, chrysene, dibenz[a,c]anthracene, and phenanthrene in excellent yields from the corresponding quinones. Although reduction of quinones with HI and phosphorus was described in the older literature, relatively drastic conditions were employed and mixtures of polyhydrogenated derivatives were the principal products. The relatively milder experimental procedure employed herein appears generally applicable to the reduction of both ortho- and para-quinones directly to the fully aromatic polycyclic arenes. The method is apparently inapplicable to quinones having an olefinic bond, such as o-naphthoquinone, since an analogous reaction of the latter provides a product of undetermined structure (unpublished result). As shown previously, phenols and hydro-quinones, implicated as intermediates in the reduction of quinones by HI, can also be smoothly deoxygenated to fully aromatic polycyclic arenes under conditions similar to those described herein. 

Similar experimental procedures can be used for the radical alkylation of electron-deficient alkenes 7 (Scheme 4). In this process, a mixture of alkene 7 and [bis(acyloxy)iodo]arenes 8 (prepared from PhI(OAc)2 and the respective... 

The present overview deals with the application of Fischer chromium carbene complexes in the benzannulation reaction for the preparation of highly substituted aromatic compounds. Before focussing on specific arenes (Section 8.5), details of the mechanism are given (Section 8.2), and the scope and limitations of the reaction are defined (Section 8.3). A short description of the experimental procedure is given thereafter (Section 8.4). Finally, the contribution deals with the application of the chromium carbene benzannulation to natural compounds and molecules with biological activity (Section 8.6). 

Surprisingly, little new research on the prototypal tung-sten-arene complex see Arene Complexes), r] -Ceih)f, has appeared, possibly because of the low-yielding and elaborate experimental procedures required for its synthesis. Photolysis of W(CO)6 in the presence of ethyne leads to the formation of benzene and rf-CdRf) W(CO)3 (101), and the solid-state molecular structure of this complex was... 

The cyclopropenylium ions underwent Friedel-Crafts-type substitution with activated arenes to give arylcyclopropenylium ions (e.g., 2, sec Section 6.A.2.1. for Experimental Procedure) and also 3-arylcyclopropenes... 

A convenient and mild experimental procedure for the preparation of (diacetoxyiodo)arenes using Select-fluor as the oxidant in acetic acid has been developed by Shreeve and coworkers [33]. This method, in particular, has been utilized in the syntheses of a chiral hypervalent iodine(III) reagent having a rigid spiro-biindane backbone [134] and the C2-symmetric chiral (diacetoxyiodo)arene 35 from the respective iodide 34 (Scheme 2.15) [169,170]. 

Electrophilic aromatic substitution reactions (Sec. 15.1) are among the best understood of all organic reactions. The qtuilitative aspects of the reactions that are discussed in textbooks include the effect substituents have on the reactivity of arenes toward electrophiles and the orientation, ortho, meta, or para, of their attack on the ring. However, relatively Httle information is given in textbooks about the quantitative differences in rates and reactivities of substituted aromatic compounds. The experimental procedures of this section provide both semiquantitative and quantitative measures of the differences in reactivity of a series of arenes toward the bromo-nium ion, Br, to produce the corresponding aryl bromides (Eq. 15.20). 

NiCl2(PCy3)2 associated with PCyj promotes the selective cross-coupling of arylto-sylates with arylboronic acids under relatively mild reaction conditions, and various functional groups are tolerated in both arene reactants. This is one of the simplest, most efficient experimental procedures for coupling arylboronic acids with aryl tosy-lates reported to date (Equation 71) [94],... 

The transformation from arenes into phenol acetates can be achieved with hypervalent iodine compounds (such as phenyliodonium acetate, PhI(OAc)2), with chromates, or under aerobic conditions. Ligands, like picolinic acids, stabilize the intermediate palladium(IV) salts. In the presence of Lewis acids or silver salts, biaryl formation takes place. The influence of different directing groups has recently been reviewed. For example, diaryl sulfones or sulfoxides having at least one heteroaryl attached can be oxidized to the corresponding aryl acetates (Scheme 5-194, Experimental Procedure below). ... 

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