Intramolecular reactions arene derivatives

FIGURE 7.16 Intramolecular acyclic terpene derivatives isommzation through the formation of allyUc cationic species and the effect of the resorcin[4]arene capsule on the product distribution of the reaction for (a) allyl alcohols and corresponding (b) acetate esters as substrates. (Adaptedfrom Ref. [66] with permission of Nature Publishing.)... 

There has been a summary of computational and experimental studies of the use of palladium complexes with A -heterocyclic carbenes (NHCs) in the asymmetric coupling of -hybridized carbon-hydrogen bonds with aryl halides. It has been shown that the electronic and catalytic properties of NHCs fused to porphyrins may be modified by varying the inner metal in the porphyrin. A DPT study of the use of palladium-NHC complexes in the asymmetric intramolecular a-arylation of 2-bromoaryl amides to give 3,3-disubstituted oxindoles (101) has been reported. The likely pathway involves insertion of the palladium into the arene-bromine bond to form a palladacycle which deprotonates to give an (9-enolate. Conversion into the C-enolate followed by reductive elimination gives the product. The intramolecular reaction of 0 a cyclopropane carbon-hydrogen bond in a 2-bromoanilide derivative has been used to form cyclopropyloxindoles, (102), in a palladium-catalysed, silver-mediated reaction. 

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],... 

The photolysis of donor-acceptor systems provides unique synthetic opportunities. Direct irradiation of the donor-acceptor systems, such as systems containing arene and amine components, leads to intramolecular electron transfer, that is, to amine cation-radical and arene anion-radical moieties. After generation, these moieties undergo cyclization reactions providing efficient synthetic routes to fV-heterocycles with a variety of ring sizes. Thus, direct irradiation of secondary amino-ethyl and aminopropyl stilbenes leads to benzazepines in improved yields (Hintz et al. 1996). As known, benzazepines are used in medicine as antidepressants. Scheme 7.44 illustrates ion-radical cyclization with the formation of benzazepine derivative (65% yield). 

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... 

Iron salts (e.g. FeCls) have been identified as new catalysts for intramolecular hydroamination. A number of olefinic tosylamides underwent the reaction at 80 °C to form the corresponding the N-tosylpyrrolidine derivatives in good yield.63 The same salt can also catalyse Markovnikov addition of electron-rich arenes and heteroarenes to styrenes, giving rise to 1,1-diarylalkanes at 80 °C.64... 

Intramolecular oxidative cyclizations in the appropriately substituted phenols and phenol ethers provide a powerful tool for the construction of various practically important polycyclic systems. Especially interesting and synthetically useful is the oxidation of the p-substituted phenols 12 with [bis(acyloxy)iodo]-arenes in the presence of an appropriate external or internal nucleophile (Nu) leading to the respective spiro dienones 15 according to Scheme 6. It is assumed that this reaction proceeds via concerted addition-elimination in the intermediate product 13, or via phenoxenium ions 14 [18 - 21]. The recently reported lack of chirality induction in the phenolic oxidation in the presence of dibenzoyltar-taric acid supports the hypothesis that of mechanism proceeding via phenoxenium ions 14 [18]. The o-substituted phenols can be oxidized similarly with the formation of the respective 2,4-cyclohexadienone derivatives. 

The A-chloroacetyl derivatives of amines appropriately substituted with electron-rich arenes often give intramolecular alkylation and not solvolysis upon irradiation in aqueous solution. These photocyclizations have proven to be quite useful and versatile methods to synthesize a variety of novel and natural aza-heterocyclic compounds. The reader is referred to Reference 13 for a comprehensive review of the scope and mechanism of these reactions. 

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