Phenol ethers trimerization

Recently the conditions have been defined under which trimerization of some phenol ethers is viable these require anodic oxidation in a flow cell with porous electrodes, using acetonitrile or trifluoroacetic acid-methylene chloride. Catechol derivative (48) and 1,2-methylenedioxybenzene were thus converted into trimers (49) and (50) respectively, in ca. 30% yield. 

The trimethylsilyloxy (TMSO) group is stable under the coupling conditions in acetonitrile (Table 12, number 6). After oxidative dimerization the TMS-ether can be mildly hydrolyzed (H+ and H2O) to the phenol or converted to a dibenzofuran. 1,2-Dialkoxybenzenes have been trimerized to triphenylenes (Table 5, numbers 7, 8). The reaction product is the triphenylene radical cation, which is reduced to the final product either by zinc powder or in a flow cell consisting of a porous anode and cathode [188]. Anodic trimerization of catechol ketals yields triphenylene ketals, which can function as a platform for receptors, for example, in an artificial caffeine receptor [190]. 

In equation 7, trimer radical (4) is produced when (3) dissociates. Whenever (4) couples with the other product of equation 7, ie, the 2,6-dimethylphenoxy radical, the tetramer is produced as described. These redistribution reactions of oligomers that proceed by ketal formation and subsequent dissociation ultimately generate terminal quinol ethers which enolize to the more stable terminal phenol (eq. 8). 

As already shown in Schemes 126 and 129, oxidation of phenols with manganese compounds provides diaryl ethers, dimers, trimers and polymers. Similarly, oxidation of phenols with Ag20 also affords diaryl ethers . However, one of the most characteristic points is that phenolic oxidation using Ag20 provides a synthetic method for quinomethanes. 

Formaldehyde reacts with phenols giving methylol (hydroxymethyl)-substituted phenols, which are the monomers in the resin. Formaldehyde also creates chemical bonds between monomers. This bond can be either of the methylene type (-CH2-) or of the methylene-ether type (-CH -O-CH -), thus forming dimers, trimers, tetramers and so on. Phenol-formaldehyde resin can be produced in two principal ways, either as resol or novolac resins. 

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