Phenols, from aryl methyl ethers

Periodic acid dihydrate, with iodine and durene to give iododurene, 51, 94 Phenols, from aryl methyl ethers, 53, 93 Phenylacetaldehyde, from 2-lithio-1,3,5-trithiane and benzyl bromide, 51, 43 Phenylacetic acid, bromination, 50, 31... 

We said earlier that simple methyl ethers are inappropriate as protecting groups for OH because they are too hard to take off again. That is usually true, but not if the OH is phenolic— ArOH is a better leaving group than ROH, so HBr will take off methyl groups from aryl methyl ethers too. 

Murugavel and Punniyamurthy developed a Cul-catalyzed one-pot synthesis of iminocoumarin aryl methyl ethers from ynal, phenol, and sulfonyl azide via a cascade [3-1-2]-cycloaddition, 1,3-pseudopericyclic ketenimine rearrangement, 1,4-conjugate addition, and aldol-type condensation at room temperature under air [195] (Scheme 8.120). 

When, furthermore, phenols (368) are coupled with 1 in the presence of a Pd° catalyst, the phenoxy-methyl-1,3-dienes 369 are produced [158]. As aryl allyl ethers, these can be made to undergo a Claisen rearrangement (205 °C, DMF) and the ensuing 2-(l,3-dienylmethyl)phenols 370 finally cydize in the presence of a trace of acid to a mixture of exo-methylene chromans 371 (major product) and dihydrobenzofur-ans 372 - a remarkable generation of functional and structural complexity from simple starting materials with 100% atom economy and underlining impressively the synthetic versatility of modern allene chemistry ... 

Singular examples to form aromatic ethers are a base-catalyzed, multistep, one-pot reaction of aryl methyl ketones with the appropriate fluorinated arylidenemalonitriles, the mercury acetate assisted synthesis of pentahalophenylvinyl ethers from vinyl acetate and the corresponding phenol, and the radical displacements in aryloxycyclohexadienones (e.g., 27) by halophenols. 2,3-Dichloro-5,6-dicyanohydroquinone (28) and products such as 29 are readily formed when cyclohexadienone 27 is treated with different phenols. 

The aryl group substitution patterns found in lignans are delineated in Scheme 2. The rings may be mono-, di-, tri-, or tetrasubstituted by the common phenolic hydroxyl, methyl ether and methylenedioxy groups. With a few exceptions (isolated notably from mammalian sources), all lignans have an oxygenated substituent para... 

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. 

Vanillin is the second largest food additive used each year. As a consequence of limited natural sources of this ubiquitous flavor and fragrance, the bulk of commercial vanillin is synthesized from phenol (19). A two-step synthesis of vanillin from glucose via DHS intermediacy was recently reported (Figure 3) (17). DHS dehydratase-catalyzed conversion of DHS into PCA is followed by formation of the methyl ether, catalyzed by catechol-O-methyltransferase, an enzyme not native to E. coli but for which the gene (comt) has been cloned from rat liver (20). In a separate step, incubation of the resulting vanillic acid with aryl-aldehyde dehydrogenase (21) affords vanillin. 

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