Addition reactions of aromatics

Photo-induced addition reaction of aromatic carbonyl compounds with alkynes gives unstable oxetanes. For example, the reaction of benzaldehyde with 2-butyne 138 gives a,(3-unsaturated carbonyl compound 139 by cleavage of intermediate oxetane [80]. 

Photo-Induced Hydrogen Abstraction and Addition Reactions of Aromatic Compounds... 

Much data has been accumulated on the relative rate constants of the addition reactions of aromatic thiyl radicals to oleflns, dienes, allenes, and acetylenes [1]. The relative rates can be evaluated by competition between two substrates reacting with thiyl radical [30]. For ArS, reversibility is the most characteristic feature of the addition reaction [31]. Thus, it is very difficult to evaluate even the relative rates of such a reversible addition reaction. 

Decarbonylation of the acylmetal intermediates has been extended to a variety of carbon-carbon forming reactions. For example, Li et al. reported decarbonylative addition reactions of aromatic aldehydes to alkynes (Scheme 7.17) [24] and acrylates [25]. An oxidative decarbonylative coupling reaction of aromatic aldehydes with 2-arylpyridines was promoted by a rhodium catalyst (Scheme 7.18) [26]. Carboxylic acid derivatives were also employed for analogous carbon-carbon bond-forming reactions through decarbonylation [27]. 

Grundmann, C. andFiommeld, FI.D. (1966) Nitrile oxides. 6. Some novel addition reactions of aromatic nitrile oxides. The Journal of Organic Chemistry, 31,157. 

Aromatic hydrocarbons, Ar-H, may also react with O and HO. Addition reactions of aromatics with HO are favored. Benzene reacts with HO to produce a reactive radical that undergoes additional reactions involved with smog formation ... 

These reversible reactions are cataly2ed by bases or acids, such as 2iac chloride and aluminum isopropoxide, or by anion-exchange resias. Ultrasonic vibrations improve the reaction rate and yield. Reaction of aromatic aldehydes or ketones with nitroparaffins yields either the nitro alcohol or the nitro olefin, depending on the catalyst. Conjugated unsaturated aldehydes or ketones and nitroparaffins (Michael addition) yield nitro-substituted carbonyl compounds rather than nitro alcohols. Condensation with keto esters gives the substituted nitro alcohols (37) keto aldehydes react preferentially at the aldehyde function. 

This trend is revealed, for example, by the rates of Diels-Alder addition reactions of anthracene, naphthacene, and pentacene, in which three, four, and five rings, respectively are linearly fused. The rate data are shown in Table 9.3. The same trend can be seen in the activation energy and the resonance energy gained when cycloreversion of the adducts 9-12 yields the aromatic compoimd, as shown in Scheme 9.3. 

Further aspects of the reaction of aromatic tertiary hydroxyl amines have been examined by more sophisticated techniques [49]. 2-Methyl-2-nitrosopropane was used as a radical trap, and the endgroups on PMMA resulting from its addition were detectable by ultraviolet spectroscopy. Electron spin resonance results on the same system have also been reported [50]. 

Unsaturated hydrocarbons undergo a variety of reactions. Experimentally, alkenes and alkynes undergo addition reactions, whereas aromatic molecules, such as benzene, undergo substitution reactions instead. Why ... 

Arynes are intermediates in certain reactions of aromatic compounds, especially in some nucleophilic substitution reactions. They are generated by abstraction of atoms or atomic groups from adjacent positions in the nucleus and react as strong electrophiles and as dienophiles in fast addition reactions. An example of a reaction occurring via an aryne is the amination of o-chlorotoluene (1) with potassium amide in liquid ammonia. According to the mechanism given, the intermediate 3-methylbenzyne (2) is first formed and subsequent addition of ammonia to the triple bond yields o-amino-toluene (3) and m-aminotoluene (4). It was found that partial rearrangement of the ortho to the meta isomer actually occurs. 

While the Friedel-Crafts acylation is a general method for the preparation of aryl ketones, and of wide scope, there is no equivalently versatile reaction for the preparation of aryl aldehydes. There are various formylation procedures known, each of limited scope. In addition to the reactions outlined above, there is the Vdsmeier reaction, the Reimer-Tiemann reaction, and the Rieche formylation reaction The latter is the reaction of aromatic compounds with 1,1-dichloromethyl ether as formylating agent in the presence of a Lewis acid catalyst. This procedure has recently gained much importance. 

Chiral modification of diorganomagnesium compounds with the dilithium salt oi (S)-l,l -bi-naphthalene-2,2 -diol gave reagents with the empirical formula 30. Good to excellent enantiose-lectivities were observed in addition reactions of aliphatic and aromatic reagents to aromatic aldehydes30,31, however, the selectivities were not satisfactory with allylic, vinylic and acetylenic reagents. 

Volume 8 Volume 9 Volume 10 Volume 12 Volume 13 Proton Transfer Addition and Elimination Reactions of Aliphatic Compounds Ester Formation and Hydrolysis and Related Reactions Electrophilic Substitution at a Saturated Carbon Atom Reactions of Aromatic Compounds Section 5. POLYMERISATION REACTIONS (3 volumes)... 

Modest diastereoselectivity was observed for the Michael addition reaction of rac-14 to 13 and these diasteromers 28-a/28-b could be separated and individually identified. The minor isomer 28-b was found to readily undergo conversion to benzoxathiin 30 when treated with BF3 etherate, presumably through the transient intermediate 29-b. The major isomer 28-a was converted by BF3 etherate to intermediate 29-a. Conversion to 30 required the use of the stronger Lewis acid TMSOTf, presumably due to the cis-stereochemistry between the methoxy and the neighboring hydrogen, making it more difficult to eliminate/aromatize. 

Addition of Vinyl and Aryl Groups. The reaction of aromatic radicals, generated by decomposition of diazonium salts, with iminium salts in the presence of TiCE in aqueous media produces secondary amines (Eq. 11.53).91 The iminium salts are formed in situ from aromatic amines and aldehydes. 

The coupling reaction of aromatic aldehydes proceeds well only in water by using VCI3 as a catalyst in the presence of A1 (Scheme 9). It should be noted that this method does not require a chlorosilane as an additive [31]. 

This reaction of aromatic aldehydes, ArCHO, resembles the Cannizzaro reaction in that the initial attack [rapid and reversible—step (1)] is by an anion—this time eCN—on the carbonyl carbon atom of one molecule, the donor (125) but instead of hydride transfer (cf. Cannizzaro, p. 216) it is now carbanion addition by (127) to the carbonyl carbon atom of the second molecule of ArCHO, the acceptor (128), that occurs. This, in common with cyanohydrin formation (p. 212) was one of the earliest reactions to have its pathway established— correctly —in 1903. The rate law commonly observed is, as might be expected,... 

Friedel-Crafts acylation reactions of aromatics are promoted by Tilv complexes.104 In some cases, a catalytic amount of the titanium compound works well (Scheme 28). In addition to acyl halides or acid anhydrides, aldehydes, ketones, and acetals can serve as electrophile equivalents for this reaction.105 The formylation of aromatic substrates in the presence of TiCl4 is known as the Rieche-Gross formylation metalated aromatics or olefins are also formylated under these conditions.106... 

Low-valent nickel complexes of bpy are also efficient electrocatalysts in the reductive coupling reaction of aromatic halides.207 Detailed investigations are in agreement with a reaction mechanism involving the oxidative addition (Equation (40)) of the organic halide to a zero valent complex.208-210 Starting from [Nin(bpy)2(X)2]0 with excess bpy, or from [Nin(bpy)3]2 +, results in the [Ni°(bpy)2]° complex (Equations (37) and (38)). However, the reactive complex is the... 

Tewari, R.S. and Shukla, R., Organophosphorus compounds. Addition reaction of 0,0-dialkyl hydrogen phosphites with substituted aromatic and long chain aliphatic aldehydes, Labdev, Part A, 9,112,1971. 

It is more difficult to interpret micellar effects upon reactions of azide ion. The behavior is normal , in the sense that k /kw 1, for deacylation, an Sn2 reaction, and addition to a carbocation (Table 4) (Cuenca, 1985). But the micellar reaction is much faster for nucleophilic aromatic substitution. Values of k /kw depend upon the substrate and are slightly larger when both N 3 and an inert counterion are present, but the trends are the same. We have no explanation for these results, although there seems to be a relation between the anomalous behavior of the azide ion in micellar reactions of aromatic substrates and its nucleophilicity in water and similar polar, hydroxylic solvents. Azide is a very powerful nucleophile towards carboca-tions, based on Ritchie s N+ scale, but in water it is much less reactive towards 2,4-dinitrohalobenzenes than predicted, whereas the reactivity of other nucleophiles fits the N+ scale (Ritchie and Sawada, 1977). Therefore the large values of k /kw may reflect the fact that azide ion is unusually unreactive in aromatic nucleophilic substitution in water, rather than that it is abnormally reactive in micelles. 

In addition to aryl halides and triflates, organometallic reagents can be utilized for the catalytic arylation reaction. The rhodium-catalyzed arylation of arylpyridines proceeds with the use of tetraarylstannanes (Equation (67)).83 The ruthenium-catalyzed reaction of aromatic ketones with arylboronates affords the ortho-arylated aromatic ketones (Equation (68)).84... 

Imides - Polyimides (PI) have been conventionally prepared by the chemical or thermal cyclodehydration of polyamic acids formed from the solution reaction of aromatic tetracarboxylic dianhydrides and aromatic diamines. The early PI were insoluble and relatively intractable. The polyamic acid was the processable intermediate. However, the polyamic acid precursor has two major shortcomings, hydrolytic instability and the evolution of volatiles during the thermal conversion to PI. In addition, residual solvent was left in adhesive tapes and prepregs to obtain tack, drape and flow. During the fabrication of components, the evolution of volatiles caused processing problems and led to porosity in the part. As work progressed on PI, other synthetic routes were investigated (e.g. reaction of esters of aromatic tetracarboxylic acids with diamines... 

Lund and coworkers [131] pioneered the use of aromatic anion radicals as mediators in a study of the catalytic reduction of bromobenzene by the electrogenerated anion radical of chrysene. Other early investigations involved the catalytic reduction of 1-bromo- and 1-chlorobutane by the anion radicals of trans-stilhene and anthracene [132], of 1-chlorohexane and 6-chloro-l-hexene by the naphthalene anion radical [133], and of 1-chlorooctane by the phenanthrene anion radical [134]. Simonet and coworkers [135] pointed out that a catalytically formed alkyl radical can react with an aromatic anion radical to form an alkylated aromatic hydrocarbon. Additional, comparatively recent work has centered on electron transfer between aromatic anion radicals and l,2-dichloro-l,2-diphenylethane [136], on reductive coupling of tert-butyl bromide with azobenzene, quinoxaline, and anthracene [137], and on the reactions of aromatic anion radicals with substituted benzyl chlorides [138], with... 

As previously discussed, activation of the iridium-phosphoramidite catalyst before addition of the reagents allows less basic nitrogen nucleophiles to be used in iridium-catalyzed allylic substitution reactions [70, 88]. Arylamines, which do not react with allylic carbonates in the presence of the combination of LI and [Ir(COD)Cl]2 as catalyst, form allylic amination products in excellent yields and selectivities when catalyzed by complex la generated in sim (Scheme 15). The scope of the reactions of aromatic amines is broad. Electron-rich and electron-neutral aromatic amines react with allylic carbonates to form allylic amines in high yields and excellent regio- and enantioselectivities as do hindered orlAo-substituted aromatic amines. Electron-poor aromatic amines require higher catalyst loadings, and the products from reactions of these substrates are formed with lower yields and selectivities. 

The reactivity of a range of alkenes in addition reactions of peroxyl radicals has been reported. Parameters that described the relationship between the activation energy and enthalpy were calculated. An activation energy of 82 kJ moP was determined for the addition of alkylperoxy radicals to isolated C=C bonds, rising by 8.5kJmor when the alkene was conjugated with an aromatic substituent. 

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