Arylmethyl ether

Starting compounds include hexa- and pentarylethanes the latter require higher temperatures (ca 100°C) than the former to break the carbon—carbon bond. In the presence of oxygen, stable radicals that are generated by other methods, eg, reduction of arylmethyl ethers and haUdes, also have been converted to diaralkyl peroxides (66). 

The Wittig rearrangement is the base-catalyzed 1.2-shift of an alkyl, allyl. benzyl, or phenyl group of an ether from oxygen to carbon. A patent claim describes the conversion of aryl arylmethyl ethers such as 21 into diarylmethanols such as 22.14... 

The demethylation of the arylmethyl ethers A in Figure 2.2 is run in dimethyl formamide (DMF structural formula see Figure 2.17) the fourfold demethylation of the aryl tetramethyl ether B is performed in molten salt and the monodemethylation of the aryl dimethyl ethers C in DMF. The selectivity of the latter reaction deserves comment. Compound C and lithium... 

On the other hand, the induction bound to the presence of chiral auxiliary was elegantly applied [184] both within the cathodic and anodic ranges. Below is described a recent example in which the anodic oxidation allowed the conversion of arylmethyl ethers bearing a chiral ethanol unit into different dimethyl ketal units. 

Benzyhc methylation of primary arylmethyl ethers can be achieved by reaction with methylmagnesium bromide in toluene at room temperature in the presence of NiCljjdppf) (2mol%) anddppf (l,l -bis(diphenylphosphino)ferrocene) (2mol%) [112]. The transformation tolerates a number of substrates, but heavily depends... 

A pinacol-type silylative dimerization of various aromatic aldehydes promoted by a cationic thiolate-bridged diruthenium complex has been reported by Flidai and co-workers (Equation (28)).344 l,2-Diaryl-l,2-disiloxyethanes 153 were isolated as the major products along with the corresponding arylmethyl silyl ethers as minor products. 

Perhaloalkanes have been found to scramble halogen atoms via consecutive halophilic reactions following carbanion generation by halophilic attack by base. S l reaction of an allylsilane has been applied in a stereocontrolled synthesis of ( )-dihydronepetalactone, and functionalized aryl and arylmethyl carbanions have been generated by reductive cleavage of aryl and arylmethyl alkyl ethers by electron transfer from alkali metals. ... 

Azzena, U. Pilo, L. Sechi, A. Metalation of arylmethyl alkyl ethers. Tetrahedron 1998, 54, 12389-12398. 

The following discussion will be focused on the effect of structural variations on the kinetics of fragmentation, the cleavage mode, and the stepwise or concerted nature of the process. Similar concepts have also been applied to the reductive cleavage reactions of other series of substrates, i.e. a-substituted acetophenones [246-250], perbenzoates [240, 251], peroxides [242, 252-256], sulfides [244, 257, 258], sulfonium salts [259-263], nitrocumenes [264, 265], arylmethyl aryl ethers and thioethers [266-270]. 

A relay Suzuki coupling of o-iodophenyl methallyl ether affords 3-arylmethyl-3-methyl-2,3-dihydrobenzofurans. ... 

Photolysis of benzene solutions of l-methoxycarbonyl-2-naphthylmethyl 2,6-di-methyl substituted phenyl ethers induces C-O cleavage with formation of 2,4-cyclohexadienone intermediates which are subsequently photo-rearranged into meta substituted phenols. In methanol, 9-anthrylmethoxy-pyrid-2-one or l-pyrenylmethoxypyrid-2-one undergo photoheterolysis to give the C-O heterolysis products l-hydroxypyrid-2-one and the arylmethyl methyl ether, together with 2-pyridone, aryl-substituted methanol and aryl aldehyde derived from homolysis of the N-O bond. Evidence shows that an intramolecular exciplex plays a crucial role in C-O bond heterolysis. 

The photochemical generation of arylmethyl cations from arylmethanols has been the topic of several papers this year. For mono-aryImethanols in which the aromatic group is phenyl, naphthyl, pyrenyl or phenanthryl, Wan has reported that ultra-violet light irradiation in aqueous alcoholic sulphuric acid solution yields the corresponding ether,presumably by way of an intermediate arylmethyl carbocation. Photolysis of (414) in aqueous alcohol to give (415) is found to proceed even in the absence of acid, while the non-cyclic analogue (416) reacts much less efficiently, even at low values of pH. This reactivity difference has been observed previously for fluorenol and benzhydrol and is attributed to extra stabilisation of the intermediate carbocation in the fluorenyl system. 

Arylmethyl cleavage reactions have also been studied in less polar solvents like saturated hydrocarbons (hexane, cyclohexane), ethers (diethyl ether, tetrahy-drofiiran, dioxane), and methylene chloride. In these solvents, ion pair chemistry is less likely and valuable information can be obtained about the photogenerated radical pairs. 

Alonsono and co-workers [146] have used substituted 1-naphthyl and phe-nylphosphonium chlorides as precursors for the generation of the corresponding arylmethyl radicals and cations in both nanosecond LFP and product studies. For instance, the salt 101 has a quantum yield for cation formation of 0.71 in methanol and the sole product observed was the corresponding methyl ether. No transient radical was observed in this solvent. In contrast, in 5% acetonitrile in dioxane, the radical was observed but now the cation was absent. No fluorescence was observed in either solvent suggesting that Si is very reactive. Redox potentials indicate that the conversion of the radical/radical ion pair to the cation/triphenyl-phosphine pair would be exothermic by some 25 kcal/mol. Therefore, both heterolytic cleavage from Si or homolytic cleavage followed by electron transfer were suggested as possible pathways for cation formation. 

Catalysis [1, 499, after citation of ref. 32], Canadian chemists323 observed that triphenylcarbinol was converted into the methyl ether in 90% yield by treatment with iodine in methanol. The reaction is general for arylmethyl alkyl ethers. Although iodine functions as a catalyst, highest yields are obtained when it it used in an... 

Alkylation with arylmethyl halides containing heteroatoms provides still another route for the introduction of functional groups onto the lower rim. Examples include (a) pyridylmethyl ethers 127d, extensively studied by Pap-palardo and coworkers (for a review, see ref. 13g), (b) nitrobenzyl ethers 127e (X = (c) halobenzyl ethers 127e (X = halogen),and (d) cy-... 

Arylmethyl methyl ethers can be alkylated (BuLi, hexane-THF, -40° RX), whereas A,A-diethylbenzyl and cinnamyl carbamates undergo disilylation using BuLi as the base. 

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