Aromatic trihalide

A wide variety of aromatic compounds can be brominated. Highly reactive ones, such as anilines and phenols, may undergo bromination at all activated positions. More selective reagents such as pyridinium bromide perbromide or tetraalkylammonium trihalides can be used in such cases.14 Moderately reactive compounds such as anilides, haloaromatics, and... 

Cyclizations with perfluoroacylating agents seem to be quite general for the synthesis of 5(2i7)-oxazolones with aromatic substituents directly bonded to the heterocyclic ring. For example, perfluoroacylation of a solution of an arylgly-cine containing a phosphorus trihalide affords 4-aryl-2-(perfluoroalkyl)-5(2//)-oxazolones (Table 7.1, Fig. 12) Similar results were obtained when amino nitriles were used as starting materials. ... 

Photocycloadditions of naphthalene derivatives to alkcnes have been recently reviewed.60 Examples of such reactions are the photocycloaddition of naphthalene to 2,3-dihy-drofuran,61 of 4-methoxy-l-naphthonitrile to acrylonitrile62 and of 2-trimethylsiloxynaph-thalene to methyl acrylate.63 2-Naphthols undergo cycloaddition with ethene in the presence of aluminum trihalides only.64 Other bicyclic aromatic compounds, e.g. A-acylindoles65-67 and /V-methylphenanthrene-9,10-dicarboximide,68 have also been studied in detail. Irradiation of 5/f-dibenzo[u,i7]cyclohepten-5-one (21) and dimethyl 2-methylfumarate (22) in dioxane gives the cyclobutane adduct 23 in 73% yield.69... 

Dr L.Deffet, Bruxelles private communication, March 10,1954 Alkenyl Aromatics of the general formula Ar. CH, CHa. C CH2, were prepd by reacting aruEliatic nyuiocarbons (at moderate temp and press) with 1,3 diolefins in the presence of a catalyst(such as boron trihalide satd with an organic carboxylic acid). The purified alkenyl aromatics can be nitrated to yield expl derivs... 

Aryltellurium trichlorides 5 (R = aryl, X = Cl) are usually yellow, very stable crystalline solids, with a slight odor of hydrochloric acid, which probably arises from the reaction of 5 with the air moisture. Contact of 5 with metallic spatulas, with moist solvents, or prolonged exposure to light must be avoided. These compounds, however, can be handled in the air with no risk of decomposition. Aryltellurium tribromides (5, R = aryl, X = Br) are yellow crystalline solids, and the triiodides (5, R = aryl, X = 1) are dark red solids. The aryltellurium tribromides and triiodides were less explored for synthetic purposes, in contrast to the aryltellurium trichlorides, which were frequently used in several synthetic transformations. The aliphatic tellurium trihalides are less stable than the aromatic ones and were much less studied and used for preparative purposes. 

The reactivity of aryltellurium trichlorides 116, the most synthetically used organotellurium trihalides, toward activated aromatics, alkenes, and alkynes is similar to the reactivity of tellurium tetrachloride toward the same substrates (Section 9.13.4.2.3). In Scheme 69, the principal features of the reactions involving aryltellurium trichlorides are presented. 

Tellurium tetrachloride and tetrabromide react with equimolar quantities of aryl mercury chlorides to produce aryl tellurium trihalides in high yields. This reaction is useful when the trichlorotelluro group is required at a specific position in the aromatic molecule or when tellurium tetrachloride does not condense in an acceptable manner with the aromatic hydrocarbon. The solvent of choice is dioxane, because mercury dichloride precipitates as the dioxane adduct, facilitating the isolation and purification of the aryl tellurium trichlorides. 

Diorgano tellurium dihalides are often the primary products of reactions producing compounds with two tellurium-carbon bonds. Such reactions arc the condensation of tellurium tetrachloride with aromatic compounds (p. 527), the addition of tellurium tetrachloride or organo tellurium trichlorides to carbon-carbon multiple bonds (p. 530, 544), and the alkylation or arylation of organo tellurium trihalides (p. 549). The symmetrical and unsymmetrical diorgano tellurium dihalides are convenient starting materials for the preparation of diorgano tellurium derivatives. 

Alkyl groups from alkyl aryl telluriums that have a stabilizing nitrogen functionality in the aromatic ring in an orr/zo-position to the tellurium atom are cleaved by bromine, iodine or sulfurylchloride. Aryl tellurium halides or trihalides are produced in these reactions. 

The dimeric trihalides form discrete molecules (Fig. 6-2). The halides dissolve readily in aromatic solvents such as benzene, in which they are dimeric. As Fig. 6-2 shows, the configuration of halogen atoms about each metal atom is far from ideally tetrahedral. The formation of such dimers is attributable to the tendency of the metal atoms to complete their octets. 

The trihalides of aluminum are very strong Lewis acids, and AICI3 finds extensive use as a Friedel-Crafts catalyst as a result of this. A wide variety of adducts are known and these exhibit an enormous range of stability, modes of bonding, structures, and properties. Aromatic hydrocarbons and alkenes only interact weakly but crystalline adducts may be isolated, for example, the clathrate complex AlyBrg CeHg. 

There are six types of tertiary aromatic arsines known, if those containing aliphatic radicals are also included ArjAs, ArAr As, ArgAlkAs, ArAlk As, ArAr AlkAs, ArAlkAlk As. For the tyj>e ArjAs, theFittig reaction forms thebasisof a method of preparation, aryl halides and arsenic trihalides reacting in ether or benzene solution in th< ))re-senee of sodium as follows ... 

The halogenated aromatic arsines combine additively with dry chlorine or bromine, yielding diarylatsine trihalides ... 

The widely applicable Fischer-Hafner method has been used to prepare arene complexes of most of the transition metals. The method involves the reaction of metal halide, aromatic hydrocarbon, aluminum trihalide, and aluminum metal, e.g. 53, 7576)(M = Cr, V),... 

Bisarene cations of Cr, Mo, and W are best synthesized by the reaction of aromatic hydrocarbon, metal halide, aluminum trihalide and aluminum metal at elevated temperature. Aromatic hydrocarbons, such as benzene, toluene, mesitylene, and hexamethylbenzene have been employed (Table III). The method is not applicable, however, when the aromatic hydrocarbon is itself reactive under Friedel-Crafts conditions. The bisarene cations are readily reduced to the neutral compounds by aqueous dithionite or, in the case of Mo and W, by alkaline disproportionation, e.g. 152),... 

Bisarene chromium compounds have been shown to undergo reversible exchange with aromatic hydrocarbons in the presence of aluminum trihalides (207). The exchange reaction has been used to improve the preparation of the bisbenzene chromium cation via the more readily prepared bismesitylene chromium cation 157b). 

The polynuclear cation [(CeHe)3Co3(CO)2] has been reported from the reaction of Hg[Co(CO)4]a or Coa(CO)0 with benzene in the presence of an aluminum trihalide (66, 114). The cation is believed to have the structure (XXXI) analogous to (7r-C5H5)3Ni3(CO)a (289). Neutral polynuclear complexes of the type (arene)Co4(CO)g (arene = benzene, toluene, anisole, />-xylene, mesitylene, tetrahydronaphthalene) have been prepared by the reaction of (RC=CH)Co2(CO)e (R = H or Ph) with norbornadiene in the appropriate aromatic solvent or in some cases by simply warming Co4(CO)i2 with the arene (247, 365). The compounds are believed to have the structure (XXXII) derived from that of Co4(CO)i2 (435) by replacement of three apical CO groups by the arene. A normal coordinate analysis has been carried out on several of... 

The nature of donor-acceptor complexes has been the subject of various NMR studies conducted as early as the 1960s. Early calorimetric studies showed that boron trihalides are capable of forming donor-acceptor complexes with a number of Lewis bases and the heats of adduct formation for some of these complexes were determined. Gaseous boron trifluoride, for example, was shown to form a ctxnplex with ethyl acetate in a highly exothermic reaction (-A// = 32.9 0.2 kcal mol ). IR and UV analysis of BF3 complexes of aromatic aldehydes indicated a o-complex with a lengthened CVO bond and a highly delocalized ir-system. More detailed structural information, however, was acquired only after closer inspection by low temperature H, B, C and F NMR studies. ... 

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