Benzyl phenyl ether, cleavage

The cleavage of anisole to lithium phenoxide by lithium in refluxing THF in the presence of biphenyl has been known since 1961,4142 and in 1963 Eisch published a practical method for forming allyllithium 32 from allyl phenyl ether 31, again using lithium in the presence of biphenyl, but at 0 °C or below.43 Twelve equivalents (a six-fold excess) of lithium metal was required for good yields in this reaction. A similar reaction takes place between benzyl phenyl ether and lithium.44... 

The difference in the electron affinity between light and heavy isotopic isomers is, in other words, the difference in the stability of their anion-radicals. Such a difference gives a valuable tool for use in probing the chemistry of anion-radicals. The difference in the stability of the ring-deuterated and ring-nondeuterated arene anion-radicals has been employed to examine the transition states for the one-electron-promoted cleavage of naphthyl methyl phenyl ether and naphthyl benzyl ether (Guthrie and Shi 1990). In this reaction, the potassium salt of fluoranthene anion-radical was an electron donor ... 

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],... 

Benzylic ethers undergo C-O cleavage only when the fragments are stabilized. Thus, benzyl phenyl (as well as naphthyl) ethers undergo... 

Aromatic Ethers in parallel with other aromatic compounds, the molecular ions of aromatic ethers are reasonably abundant. Cleavage of the bond P to the ring, as shown in reaction (6.48) for methyl phenyl ether, is typical of aromatic ethers, and forms a structure-specific ion of m/z 93. Benzyl ethers, on the other hand, produce m/z 91. Another typical reaction is hydrogen transfer, followed... 

In this reaction, only the benzylic carbonate can react readily since cleavage of the benzylic carbon-oxygen bond leads to a stabilized carbocation while no such stabilization would exist for the hypothetical products which would be obtained by cleavage of the phenyl carbonate. The benzylic carbocation intermediate which is formed can either eliminate to the corresponding styrene 4 or recombine with the nucleophilic methanol which is formed by decarboxylation. It is the latter reaction which appears to prevail at room temperature as the ether 2 can be isolated in excellent yield. Subsequent heating in the presence of acid catalyst drives the reaction to the elimination product 6 and free methanol. 

Entry 9 in Table 3.13 is an example of a safety-catch linker, which requires activation by TFA-mediated cleavage of a tert-butyl ether. The unactivated 2-(tm-butoxyj-phenyl esters are cleaved by amines 700 times more slowly than the corresponding 2-hydroxyphenyl esters [289]. A similar linker has been described [290], in which a benzyl ether is used instead of a ferf-butyl ether. Activation of this linker by debenzy-lation was achieved by treatment with HF or HBr/TFA [290]. 

Alkaline hydrolysis of lignin increases the number of reactive benzylic hydroxyl groups and may also be important in further depolymerizing the lignin once the oxidative-cleavage reaction has occurred. The formation of a p-electron-withdrawing -CHO substituent on aryl lignin units should increase the rate of hydrolysis of the ether bonds (26). Hydrolysis also forms p-phenylate ions, which then protect the benzaldehyde from further reaction via the Cannizzaro reaction, as mentioned earlier. 

Benzoin Ethers Benzoin ethers were the most widely used photoinitiators for a long time [13-15]. The cleavage process in the triplet state (10.8) is very fast compared to that of some related structures (>1010 s ). The cleavage yield is almost unity for 2,2-dimethoxy—2 phenyl-acetophenone DMPA or 2-methoxy -2 phenyl acetophenone BME. A secondary photochemical cleavage (the possible thermal cleavage is less efficient) can arise in the dimethoxy benzyl radical and leads to a methyl R" radical and an alkyl benzoate. 

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