Arenes intramolecular reaction with

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... 

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. 

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... 

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)... 

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. 

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]. 

The last two chapters by Hoffmann and Ramamurthy deal with a collection of photochemical reactions with arenes, the ortho-, meta- and para photocycloadditions and with a conceptually exciting concept in organic photochemistry, the use of contrained media. Retigeranic acid (16, by formal asymmetric synthesis) was synthesized via a fabulous reaction sequence involving an intramolecular meta photocycloaddition as key step [16]. 

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]. 

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. 

The next selectivity issue, exo/endo preferences, can be predicted for both the ortho and meta modes of cycloaddition on the basis of secondly orbital interactions (FMO treatment) and by electrostatic considerations involving polarized species (54) and (27). In general, intermolecular reactions with simple al-kenes proceed with endo selectivity. Heteroatom-substituted or polarized alkenes (equation 11) give exolendo mixtures, whose composition can be explained by electrostatic considerations. Intramolecular cycloadditions of simple alkenes and arenes joined by a three-atom tether generally proceed with high exo selectivity due in part to orbital alignment effects. In all cases, alkene geometry is preserved, except for sterically encumbered alkenes, in which case excitation transfer from the arene to the alkene can occur. 

From a synthetic point of view, bond forming steps are the most important reactions of radical ions [202]. Several principle possibilities have been described in Section 8.1 and are summarized in Scheme 52. Many carbo- and heterocyclic ring systems can be constructed by (inter- and intramolecular) radical addition to alkenes, alkynes, or arenes. Coupling of carbonyl radical anions leads to pinacols either intra-or inter-molecular which can be further modified to give 1,2-diols, acyloins or alkenes. Radical combination reactions with alkyl radicals afford the opportunity to synthesize macrocyclic rings. These radical ion-radical pairs can be generated most efficiently by inter- or intramolecular photoinduced electron transfer. 

Chloromethyl groups are an obvious starting point for the introduction of further functions, e.g. via the Arbuzov reaction. Bidentate A-donor groups were introduced by nucleophilic substitution with suitable diamines . Especially interesting is the intramolecular bridging of adjacent phenolic units by reaction with bis-nucleophiles. Thus, derivatives with C2 symmetry have been obtained from chloromethylated calix[4]arenes , while a... 

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... 

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