Substituted arene

Alkyl substituted arenes give 1 4 cyclohexadienes m which the alkyl group is a substituent on the double bond... 

The preparation of amines by the methods described m this section involves the prior synthesis and isolation of some reducible material that has a carbon-nitrogen bond an azide a nitrile a nitro substituted arene or an amide The following section describes a method that combines the two steps of carbon-nitrogen bond formation and reduction into a single operation Like the reduction of amides it offers the possibility of prepar mg primary secondary or tertiary amines by proper choice of starting materials... 

Interactive to use a web-based palette to predict products from electrophilic aromatic substitutions on substituted arenes. 

Three configurational isomers are possible for a diazoanhydride with the same (substituted) arene residues on both sides the (Z),(Z), the (Z (E), and the (E),(E), as shown in Scheme 5-15, formulas 5.4, 5.5, and 5.6. Kauffmann et al. think that in their product the residues attached to both azo groups are in the (Z)-configuration. However, their arguments are not clearly convincing. 

A subsidiary approach involves nuclear modification of the arylsilanes so obtained. The requisite organometallics can be prepared from aryl halides, or by deprotonation of a suitably activated (c.g. methoxy-substituted) arene. A more specialized route involves cycloaddition between alkynylsilanes and diynes. 

Novel ruthenium-amidinate complexes of the type (j -CgHsRlRufamidina-te)X (R = Me, OMe, F X = Cl, Br, OTf) and [Ru(amidinate)(MeCN)4][PF6] have been synthesized by photochemical displacement of the benzene ligand in (j -CgHglRufamidinatelX by substituted arenes or MeCN. The acetonitrile ligands of [Ru(amidinate)(MeCN)4][PF6] are easily replaceable by other cr-donor ligands (L) such as pyridines, phosphines, and isocyanides to afford the corresponding derivatives [Ru(amidinate)(MeCN) (L)4 ][PF6] n — 1, 2). These reactions are summarized in Scheme 142. ... 

Usually, a-bromo-substituted arenes have been prepared through the reaction of arenes with bromine under ultraviolet irradiation. In the presence of benzoyl peroxide, N-bromosuccinimide can also be used for this purpose. 

We found that the reaction of arenes with a calculated amount of BTMA Br3 in refluxing benzene in the presence of AIBN gave a-bromo-substituted arenes in fairly good yields. In this method, it was found that AIBN was a more effective free radical initiator than benzoyl peroxide (Fig. 15) (ref. 22). 

This method ensures the deposition of very reactive metal nanoparticles that require no activation steps before use. We shall review here the following examples of catalytic reactions that are of interest in line chemical synthesis (a) the hydrogenation of substituted arenes, (b) the selective hydrogenation of a, 3-unsaturated carbonyl compounds, (c) the arylation of alkenes with aryl halides (Heck reaction). The efficiency and selectivity of commercial catalysts and of differently prepared nanosized metal systems will be compared. 

Fig. 5 Mulliken dependence of the charge-transfer energy in the series of dibromine complexes with alkyl and chloro-substituted arenes and alkene donors (data from [45,65])...

Alkenones were used by Rao and coworkers [40] to prepare cyclohexane derivatives which, for example, can be transformed into substituted arenes in a single step. Another interesting intermolecular Michael/intramolecular aldol reaction sequence for the construction of the highly substituted 2-hydroxybicy-clo[3.2.1]octan-8-one framework has been described by Rodriguez group [41]. This process can be extended to a three- and even a fourfold domino reaction [41a, 42, 43],... 

Reaction of rhenium atoms with alkyl-substituted arenes forms dirhenium- l-arylidene compounds (2 2) (Figure 3). The products require insertion, presumably sequential, into two carbon-hydrogen bonds of the alkyl substituent. These reactions seem highly specific and require only the presence of an alkyl-substituted benzene that possesses a CH2 or CH3 substituent. Thus, co-condensation of rhenium atoms with ethylbenzene gives two isomers (see Figure 3) in which the products arise from insertion into the carbon-hydrogen bonds of the methylene or the methyl group. The product distribution in this reaction is in accord with statistical attack at all available sp3 C-H bonds. 

An orthometallation procedure for the preparation of condensed iso-thiazolium salts from appropriately substituted arenes has been described earlier in this Section (Scheme 117)180 an example illustrating the way in which this approach can be elaborated to the synthesis of condensed 1,2-dithiolylium perchlorates is given in Scheme 123. 

Arene-l,2-dichalcogenolene ligands are generally stable as 1,2-dichalcogenols or 1,2-dichalcogenolato sodium salts.55,56 Aromatic 1,2-dithiolates can be prepared by following two different synthetic approaches, shown for bdt2- in Scheme 6, which start either from dihalo-substituted arenes or from mercapto-or vicinal dimercapto- arenes.57 62... 

In the former case, the dibromo- or dichloro-substituted arene is reacted with cuprous or sodium thiolates to give vicinal thioethers, which can be reductively dealkylated, for example with Na/NH3, to give the dithiols.63 Alternatively, benzenethiol is reacted with ra-BuLi, and the resulting lithiated product is made to react with elemental sulfur to give the 1,2-dithiolate salt. 

Haloarenes have been found to undergo nucleopilic substitution when irradiated with the triphenyl stannyl anion46, reacting via a radical S l mechanism. In many cases the reaction will only occur under photochemical conditions. The reaction is found to proceed with chloro- and bromo-substituted arenes, but not iodo-compounds. The anion is produced either by treatment of triphenyltin chloride or hexaphenylditin with sodium metal in liquid ammonia, and will react with a wide variety of arenes (reaction 30). 

The most fundamental reaction is the alkylation of benzene with ethene.38,38a-38c Arylation of inactivated alkenes with inactivated arenes proceeds with the aid of a binuclear Ir(m) catalyst, [Ir(/x-acac-0,0,C3)(acac-0,0)(acac-C3)]2, to afford anti-Markovnikov hydroarylation products (Equation (33)). The iridium-catalyzed reaction of benzene with ethene at 180 °G for 3 h gives ethylbenzene (TN = 455, TOF = 0.0421 s 1). The reaction of benzene with propene leads to the formation of /z-propylbenzene and isopropylbenzene in 61% and 39% selectivities (TN = 13, TOF = 0.0110s-1). The catalytic reaction of the dinuclear Ir complex is shown to proceed via the formation of a mononuclear bis-acac-0,0 phenyl-Ir(m) species.388 The interesting aspect is the lack of /3-hydride elimination from the aryliridium intermediates giving the olefinic products. The reaction of substituted arenes with olefins provides a mixture of regioisomers. For example, the reaction of toluene with ethene affords m- and />-isomers in 63% and 37% selectivity, respectively. 

The N-fluoroimide effects direct aromatic fluorination at 22°, with high preference for ort/io-substitution of substituted arenes. It also converts NaC(CH3)-(COOC2H5)2 into FC(CH,)(COOC2Hs)2 in 96% yield.1... 

Correlation between o parameters and k (CO) for substituted arene Cr(CO)3 complexes... 

The methodology is useful for a variety of synthetic purposes. The cycloadditions are not subject to steric hindrance. Thus diyne cycloadditions to 2,5-disubstituted furans or pyrroles, followed by elimination of the oxygen or nitrogen bridges, provides an excellent, short route to peri-substituted arenes, as in the following examples 4 6 8... 

The mass resolved lcR2PI spectrum of the bare chiral chromophore Cr = (R)-(+)-l-phenyl-1-propanol, shows three intense signals at 37577 (A), 37618 (B), and 37624 cm (C) in the electronic Sj — Sq band origin region. A similar triplet falls at 38106, 38148, and 38155 cm . This pattern is common to substituted arenes and is interpreted as due to three stable conformers. Quantum chemical calculations at the RF1F/3-21G and B3LYP/6-31G levels of theory confirm this hypothesis. 

Electron-rich olefins with substituents Y = phenyl, vinyl, amino, or alkoxy can be coupled by anodic oxidation to tail-tail dimers being either deprotonated to dienes and/or substituted a to Y, depending on Y and the reaction conditions (Eq. 6). Alkyl substituted arenes can be dehydrodimer-ized to diphenyls or diphenylmethanes depending on the kind of substitution (Eq. 7). 

The Dotz benzannulation reaction yields either arene chromium tricarbonyl complexes or the decomplexed phenols, depending on the work-up conditions. Because of the instability of hydroxy-substituted arene chromium tricarbonyl complexes, yields of the latter tend to be low. High yields of arene complexes can, however, be obtained by in situ silylation of the crude product of the benzannulation reaction [336]. Oxidative work-up yields either decomplexed phenols or the corresponding quinones. Treatment of the benzannulation products with phosphines also leads to decomplexed phenols [272]. 

The competihve hydrogenation of alkyl-substituted arenes was also performed with lr(0) nanoparhcles [49]. Using toluene as a standard substrate, several toluene/ benzene and toluene/monoalkylbenzene hydrogenation experiments were conducted in order to determine the selectivity constants of the transition-metal nanoparticles. These selechvity constants can be used to predict the relative reactivity of any other couple of monoalkylbenzenes. A series of initial reaction... 

The use of several rhodacyclopentadiene complexes in syntheses of polycyclic aromatic compounds has been described by Miiller. In general, alkynes displace the rhodium center to give substituted arenes. In this way, complex 279 [from l,2- PhC=CC(0) 2C6H4] reacts with PhC=CC=CR (R = Me, Ph) to give 280 (R = Me, Ph) (Scheme 61). ... 

Ring-Chain Equilibrium CoNSTANrs" por o-Hydroxymethyl-SuBSTiTUTED Arene Carbal.dehydes AND Arylketones (34-36)... 

Electrochemical reduction of aryl sulphones in methanol leads to cleavage of one carbon-sulphur bond in a two-electron process. Alkyl aryl sulphones with an electron donating substituent in the aryl ring give the arenesulphinic acid and an alkane [68, 69]. Methyl phenyl sulphone and alkyl aryl sulphones with an electron withdrawing substituent in the aryl ring are cleaved to the substituted arene and the alkylsulphinic acid [70], see Scheme 5.2. In addition, a bulky orfAo-substituent such as tert.-butyl favours cleavage to the arene and alkanesulphinic acid [71]. 

From o-Dihalogen-Substituted Arenes and Related Substances. 375... 

The reaction of different aryl fluorides 23 with lithium and a catalytic amount of naphthalene (7%) in THF at —30°C afforded a solution of the corresponding aryllithiums 24, which after treatment with an electrophile (E) and final hydrolysis gave the expected substituted arenes 25 (Scheme 10) . 

McEwan and co-worker" examined the acid-catalyzed decomposition of unsymmetrical benzhydryl azides 18 and some related species (Fig. 13.11). The aryl migration step showed very little discrimination between aryl rings with electron-donating and those with electron-withdrawing substituents. This low selectivity was judged to be more consistent with formation of a discrete nitrenium ion intermediate (19). These workers reasoned that a concerted migration would exhibit higher selectivity toward donor-substituted arenes, because in that mechanism the electrons from the arene would participate in the reaction. 

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