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Arene intramolecular reaction

Pandey and co-workers have generated arene radical cations by PET from electron-rich aromatic rings [119]. The photoreaction is apparently initiated by single-electron transfer from the excited state of the arene to ground state 1,4-dicyanonaphthalene (DCN) in an aerated aqueous solution of acetonitrile. Intramolecular reaction with nucleophiles leads to anellated products regio-specifically. The author explains the regiospecifidty of the cyclization step from... [Pg.91]

Palladium(0)-catalyzed cross-coupling of aryl halides and alkenes (i.e., the Heck reaction) is widely used in organic chemistry. Oxidative Heck reactions can be achieved by forming the Pd -aryl intermediate via direct palladation of an arene C - H bond. Intramolecular reactions of this type were described in Sect. 4.1.2, but considerable effort has also been directed toward the development of intermolecular reactions. Early examples by Fu-jiwara and others used organic peroxides and related oxidants to promote catalytic turnover [182-184]. This section will highlight several recent examples that use BQ or dioxygen as the stoichiometric oxidant. [Pg.103]

Singlet oxygen reacts with binaphthylphosphine derivatives such as 1, l -binaphthyldi-/-butylphosphine to form the corresponding binaphthyl-2-oxide phosphine oxides. This intramolecular arene epoxidation reaction proceeds with complete retention of stereochemistry. The binaphthyl-2-oxide di-/-butylphosphine oxide undergoes a slow NIH rearrangement to form the corresponding hydroxylated product. A transient phospha-dioxirane intermediate has been directly observed by low-temperature NMR.241... [Pg.120]

Superacid-catalysed intramolecular reactions of some dicationic electrophiles have been investigated.36 The positively charged centres migrate apart and this chemistry gives a new synthetic route to aza-polycyclic compounds. The polycyclic compound (26) can, for example, be formed from reaction of 2-phenyl-3-(l-hydroxy-2-phenyl-ethyl)quinoline (25) with CF3SO3H at 25 °C, loss of water and benzene being involved. Highly diastereoselective polycyclization of homo(polyprenyl)arenes [e.g. (27)... [Pg.192]

In our attempt to extend the coupling reaction of arenes with alkenes to the coupling with alkynes, as shown in Scheme 4, it was found that the reaction of arenes with ethyl propiolate in TFA (trifluoroacetic acid) gave addition products instead of a coupling product [3]. This addition reaction has been extended to various alkynes and various arenes and also to intramolecular reactions for synthesis of heterocycles such as coumarins, quinolines, and thiocoumarins. [Pg.195]

Photolysis of chromium alkoxycarbene complexes 1193 leads to isochroman-4-ones 1194 via an intramolecular Friedel-Crafts acylation of the arene. The reaction yield is highly dependent upon the amount of ZnCl2 present, which varies considerably for specific substrates (Equation 458, Table 56) <1998JOC1462>. [Pg.671]

The most characteristic photochemical reaction of aromatic compounds is their cydoaddition with alkenes. The intramolecular reaction is suitable for the synthesis of complex structures, such as those depicted in Scheme 9.49, where [3+2]-photocycloaddition leads to structures which resemble natural products (aphidico-line and stemoclinone). An interaction of the arene singlet excited state with the alkene ground state gives rise to the meta adduct [83, 84]. [Pg.311]

A solution of 1.38g (0.01 mol) of 87 and 5.3g (0.1 mol) 88 in lOOmL of cyclohexane in a fused silica tube was irradiated (six 15 W low pressure mercury arc lamps) under nitrogen until complete consumption of the arene had occurred. The cyclohexane solution was decanted from the immiscible orange oil of acrylonitrile cyclobutane dimers and rotary evaporated. The photoadduct 89 comprised 95% of the oil residue and was further purified by flash chromatography (32-62 mm silica) with petroleum ether/diethyl ether (5 3) as eluant. For an intramolecular reaction of this type see [25]. [Pg.545]

Arenes, especially electron-rich ones, have been found to react with alkynes in the presence of Pd(ll) or Pt(ll) species in a mixed solvent containing CF3COOH (Eq. 81) [158-160]. The intramolecular reaction is also possible (Eq. 82). The mechanism proposed for the reaction involves aromatic pallada-tion to form arylpalladium species as in Fujiwara-Moritani reaction, insertion of an alkyne, and protonolysis of the resulted vinylpalladium intermediate. [Pg.237]

Friedel-Crafts alkylation reactions are, in general, accompanied by isomerization processes. Olah et a/. reported the results of the water-promoted, AlCb-catalyzed isomerization of o-, m- and p-di-f-bu-tylbenzene. No ortho isomer was present in the equilibrium mixture. The isomerization of o-di-r-bu-tylbenzene was very rapid largely due to relief of steric strain. In these and other related sterically hindered arenes, intramolecular isomerization and not dealkylation was observed. Isomerization of di-and mono-methylnaphthalenes, catalyzed by HF-BF3, was also reported. Isomerization of /i-alkyl-toluenes and -xylenes, catalyzed by AICI3 at room temperature, afforded chiefly /n-/i-alkyltoluenes and /n-/i-alkylxylenes, respectively. The process leading to the meta isomer has a lower energy than the other processes. [Pg.327]

Although intermolecular Heck-type reactions of carbocyclic arenes are uncommon, related intramolecular reactions are well precedented as illustrated by the following two examples [73, 74]. [Pg.18]

The formation of an arene oxide intermediate, exemplified below, during the gold-catalyzed intramolecular reaction between furans and alkynes to form phenols was observed experimentally for the first time <05AG(I)279. ... [Pg.189]

The most common mechanism of C-H bond cleavage in the arylation examples discussed above has been assumed to be electrophilic aromatic substitution involving reaction of an electrophilic palladium catalyst with an electron rich, nucleophilic aromatic ring. In order to effect direct arylation on simple, electron deficient arenes, a basic directing group or intramolecular reaction is usually necessary to enable formation of a metalocycle. As a brief introduction to the effect of this area on the functionalization of indoles and pyrroles, we provide an overview of the mechanistic... [Pg.102]

Friedel-Crafts acylation. ReBr(CO)j is a novel catalyst for acylation of arenes using acyl halides. Indanones and tetralones are generated in the intramolecular reactions. [Pg.49]

The failure of tertiary (AI,IV-dimethylaminoalkyl)arenes and stilbenes to undergo intramolecular addition may reflect structural differences between inter- vs. intramolecular exciplexes. Polar solvents are generally required for the observation of in-termolecular addition reactions of tertiary amine exciplexes. Equilibration between solvent-separated and radical ion pairs may be necessary in order to achieve an appropriate reaction trajectory for a-C-H proton transfer. In the case of intramolecular exciplexes with short chain linkers, electron transfer in polar solvents may occur in extended geometries which are inappropriate for proton transfer and chain folding may not compete effectively with exciplex decay. The exceptions to these generalizations, benzene and styrene, form more localized anion radicals which undergo both inter- and intramolecular reactions with tertiary amine cation radicals in nonpolar solvents. [Pg.24]

Lewis acids are also effective in activating a-diazo ketones towards intramolecular nucleophilic attack by alkenes and arenes. The reaction has been used effectively for the synthesis of cy-clopentenones (eq 27) starting with 8, /-unsaturated diazo ketones derived from the corresponding acid chloride and diazomethane. It has also been used to initiate polyalkene cyclizations (eq 28). Typically, boron trifluoride etherate is used as the Lewis acid, and electron-rich alkenes are most effective providing the best yields of annulation products. [Pg.148]

In addition to the several reports of intermolecular Fujiwara-Moritani reactions, there have been a nnmber of examples of intramolecular reactions, both stoichiometric and catalytic in palladinm. In considering an intramolecular oxidative Heck reaction, one can again draw a direct analogy to the classical Heck reaction (Figure 9.3). In the standard Heck reaction, a halogenated arene nndergoes an oxidative addition by palladium(0), followed by alkene insertion and jS-hydride elimination. In an oxidative version, a C—H bond of... [Pg.360]

Intramolecular reactions of the two arene components linked by a tether can occur regioselectively because of the geometric constraints. An example of an intramolecular direct arylation controlled by a temporary tether is shown in Equation 19.148. In this synthesis of dioncophylline C, two important features of intramolecular direct arylation are illustrated. First, intramolecular arylation reactions are typically used for the construction of five-, six- (as shown in Equation 19.148), and seven-membered rings. Second, direct arylation tends to occur at the less-hindered aryl C-H bond. [Pg.944]

Many binuclear model complexes of tyrosinase have been synthesized and studied in the last two decades. Karlin and co-workers showed the first example of arene hydroxylation by a well-defined jf-peroxo-dicopper(II) complex (54-57). The intramolecular reaction has been demonstrated to proceed by an electrophilic oxidative mechanism, according to extensive kinetic, Hammett correlation, and resonance Raman studies on the parent ligand complex and analogs (Fig. 2) (57). [Pg.780]

An extension of Hashmi s Au(III)-catalyzed phenol synthesis [81] to furan substrates 9 bearing an additional alkyne moiety allowed the preparation of C6-C7-heterofused benzofuran 11 (Scheme 9.3) [82]. According to the proposed mechanism, the Au(III)-catalyzed arene formation reaction generates o-alkynylphenol 10. A subsequent Au(III)-catalyzed cycloisomerization of the latter, following the general mechanism for an intramolecular nucleophilic addition of heteroatom to transition metal-activated carbon-carbon multiple bonds, gives 11 (Scheme 9.3). [Pg.319]

Buchwald described an oxypalladation reaction, followed by a C-H functionalization. This entirely intramolecular reaction is initiated through a 5-exo Wacker-type cychzation of 84. The resulting a-alkyl-paUadium intermediate M provides subsequent C-H activation at the neighboring arene, which allows a paUadium(II) intermediate N bearing a-alkyl and o-aryl substituents, respectively. Reductive elimination provides the C-C bond installation of 85 with the concomitant release of a paUadium(O) catalyst state. Reoxidation imder aerobic conditions, most probably through a palladium(II) -peroxo complex and protonolysis with the acetic add hber-ated in the previous steps, regenerates the original paUadium(II) diacetate catalyst. [Pg.1277]


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See also in sourсe #XX -- [ Pg.363 ]




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Alkynes intramolecular reactions, with arenes

Arene reaction

Arenes intramolecular reaction with

Arenes intramolecular reactions, termination

Arenes reaction

Heck reaction arene analogs, intramolecular reactions

Intramolecular Reaction of Haloaryl-Linked Arenes

Intramolecular reactions arene derivatives

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