Phenyl alkyl ethers, cleavage

Another example of cleavage of the ether C-O bond is dealkylation from phenyl alkyl ethers bonded to (r 5-C5H5)Ru entity by a base such as KOH or RO [88]. 

Cleavage conditions for alkyl benzyl ethers prepared from acid-labile benzyl alcohols are similar to those for the corresponding benzyl esters (Table 3.30). Aryl benzyl ethers, however, are generally cleaved more easily by acidolysis than esters or alkyl ethers. Phenols etherified with hydroxymethyl polystyrene, for instance, can even be released by treatment with TFA (Entry 1, Table 3.31). It has also been shown that Wang resin derived phenyl ethers are less stable than Wang resin derived esters towards refluxing acetic acid [29]. Alternatively, boron tribromide may be used to cleave aryl ethers from hydroxymethyl polystyrene [573],... 

The corrinoid-mediated reduction of polyhaloethenes has been the subject of a recent study, which reports reaction via homolytic C-halogen bond fission. The elimination of a further halogen radical affords haloalkynes, which lead to acetylene itself.56 The electron transfer-induced reductive cleavage of alkyl phenyl ethers with lithium naphthalenide has been re-examined in a study which showed that it is possible to reverse regioselectivity of the cleavage (i.e. ArOR to ArH or ArOH) by introduction of a positive charge adjacent to the alkyl ether bond.57 A radical intermediate has been detected by ESR spectroscopy in the reduction of imines to amines with formic acid58 which infers reacts takes place via Lukasiewicz s mechanism.59... 

Phenyl alkyl sulfides undergo reactions typical of their counterpart ethers but show additional skeletal rearrangements that complicate structure elucidation. Elimination of 8H is common in compounds whose usual cleavage pathways are less facile. Aromatic disulfides often undergo additional losses of 83 and/or H82. 

Homoallyl ethers or sulfides.1 gem-Methoxy(phenylthio)alkanes (2), prepared by reaction of 1 with alkyl halides, react with allyltributyltin compounds in the presence of a Lewis acid to form either homoallyl methyl ethers or homoallyl phenyl sulfides. Use of BF3 etherate results in selective cleavage of the phenylthio group to provide homoallyl ethers, whereas TiCl effects cleavage of the methoxy group with formation of homoallyl sulfides. 

The degradation products of GOS were 1,3-dimethyl pyrogallol (HI), 2-(2 ,6 dimethoxy phenoxy)-2-propenal (Vni), 2-(2, 6 -dimethoxy phenoxy)-3-hydroxypropanal (XII), and GOS-Dimer. These products show that the reaction includes oxidative polymerization and the cleavage of -0-4 ether linkage following the alkyl-phenyl cleavage. This depolymerization pathway of GOS is also similar to that of SOS (Table I). 

Hie GOG-Dimer formed from the lignin dimer compound (GOG) by laccase III was also degraded by laccase HI, resulting in the formation of compounds (I), (VI), and biphenyl dimer of 2-methoxy-l,4-benzoquinone (DC). This indicates that GOG-Dimer also suffers the cleavage of -0-4 ether linkage via the alkyl-phenyl cleavage. 

For primary alkyl phenyl ethers 47, their hthiation under catalytic conditions (DTBB, 5%) in THF at room temperature gave the expected alkyUithiums, which by reaction with carbonyl compounds afforded, after hydrolysis, the expected alcohols 48 (Scheme 15) . In this case, only the O—Caiiyi bond cleavage was observed . On the other hand, the reaction shown in Scheme 15 failed for secondary (R = i-Pr) or tertiary (R = f-Bu) starting materials. 

The cleavage of an unsymmetrical acyclic ether yields two alkyl phenyl tellurium products. The product distribution is determined by the relative ease of the cleavage of the ether bond by an SN2 process2 ... 

Cleavage of ethers. All, cleaves alkyl phenyl ethers in refluxing CH,CN or CS, selectively to phenols and alkyl iodides. The regioselectivity is the same as that shown by AICI but the reagent is more reactive. Cleavage of dialkyl ethers requires elevated temperatures and long reaction times. 

Alkylation of fl-aryleyclopentanones. Addition of 10 mole% of CuCN to the lithium enolate prepared from /3-arylcyclopentanones and LDA increases the amount of the less stable product of alkylation. Polyalkylation is also suppressed. Similar results are obtained when methyl- or phenylcopper is added to the enolate prepared by alkyUithium cleavage of trimethylsilyl enol ethers. The mechanism by which Cu(I) influences these alkylations is not as yet understood. The regiospecificity of enolate formation in the example Illustrated in equation (I) has been attributed to a directing efiect of the proximate phenyl group. This effect is also observed in the deprotonation of -arylcyclohexanones. Quantitative, but not qualitative, differences exist between five- and six-membered rings, probably because of conformational differences. ... 

The cleavage of an unsymmetrical acyclic ether yields two alkyl phenyl tellurium products. 

As mentioned in the discussion of the pathways to indoles (Scheme 27), a detailed indole synthesis with two points of diversity based on the Heck reaction has been reported [164]. The indole core structure was synthesized via a 5-exo-tng transition state, which provided the exocyclic double bond that subsequently underwent exo to endo double-bond migration. The anthranilate building block was prepared in solution and immobilized by a method previously described for the loading of 2-aminobenzophenones [Ij. After Fmoc cleavage, the resulting 4-bromo-3-amino-phenyl ether was treated with acid chlorides and pyridine in CH2CI2. As outlined in Scheme 29, alkylation of the anilide with substituted allyl bromides was achieved in the presence of lithium benzyloxazoHdinone in THF. The reaction mixture was treated with base for 1 h and then an aUylic halide was added and the mixture was vortexed for 6 h at room temperature. The alkylation reactions were... 

---