Phenols => aryl aldehydes

Nicolaou prepared the aryl aldehyde 84 by an efficient five-step sequence, as shown in Scheme 3.14. Beginning with 2-bromojuglone (36), radical allylation afforded the allylquinone 88 (75 %). Benzylation of the phenol group followed by... 

The same laboratory has prepared three tridentate zinc chelates from chiral tertiary amino phenolic alcohols and used them for enantioselective addition of diethylzinc to aryl aldehydes in 70-87% ee. Results with the ligand 4 [from (1S,2S)-(+ )-pseudoephedrine] are typical. 

Oxidation of aryl aldehydes or aryl ketones to phenols using basic hydrogen peroxide conditions. Cf. Baeyer-Villiger oxidation. 

The Dakin Reaction allows the preparation of phenols from aryl aldehydes or aryl ketones via oxidation with hydrogen peroxide in the presence of base. The aryl formate or alkanoate formed as an intermediate is subsequently saponified to yield the substituted phenol product. 

Peroxysulfuric acid, PBA and MPPA, common reagents of the past, appear less frequently in the current literature. Basic 30% hydrogen peroxide or r-butylhydroperoxide have special utility for oxidation of cyclobutanones and strained, bridged cycloalkanones to lactones. Basic 3- % hydrogen peroxide is used in the Dakin oxidation of aryl aldehydes to phenols, while peroxymonophosphoric acid oxidizes aryl ketones to phenolic acetates. ... 

In addition to the aza-bicyclohcptanoncs of type 96 described above, some examples of stereospccific cyclization (Sec. C.4) leading to dihydro-1,3-bcnzoxa7.ine derivatives. starting from phenolic substrate, primary amine, and two equivalents of aryl aldehyde are reported in the literature. ... 

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. 

Acetals of a-bromo aldehydes are obtainable from <%,/ -dibromoalkyl acetates by an analogous procedure in which these esters are prepared from enol acetates and bromine and are then converted into acetals by means of alcohols.939 A simple synthesis of <%-keto aldehydes is to treat a-brominated phenacyl phenyl ethers with alkoxides or phenoxides.940 This method is particularly useful for the preparation of aryl acetals because it avoids the side reactions that can complicate reactions between phenols and aldehydes in an acidic medium. 

This reaction was initially reported by Dakin in 1909. It is the preparation of phenols from aryl aldehydes or aryl ketones involving the oxidation of corresponding aromatic compounds by hydrogen peroxide in the presence of a base and subsequent hydrolysis of the aryl formate or alkylcarboxylate intermediates. Therefore, this reaction is generally known as the Dakin reaction. It has been reported that the para-or ortho- substituents (such as OH, NH2) on aryl aldehydes or aryl ketones will facilitate this reaction, especially for the ortho OH group, which accelerates the reaction via the formation of an intfamolecular hydrogen bonding. ... 

This reaction has general applications in the synthesis of phenols from aryl aldehydes or aryl ketones. 

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. 

Any functional group that undergoes oxidation with permanganate interferes with the test (phenols, aryl amines, most aldehydes, primary and secondary alcohols, etc.). 

Several name reactions are promoted by AICI3. For example, the Darzens-Nenitzescu reaction is simply the acylation of alkenes. The Ferrario reaction generates phenoxathiins from diphenyl ethers (eq 19) The rearrangement of acyloxy aromatic systems is known as the Fries rearrangement (eq 20). Aryl aldehydes are produced by the Gatterman aldehyde synthesis (eq 21). The initial step of the Haworth phenanthrene synthesis makes use of a Friedel-Crafts acylation. The acylation of phenolic cort tounds is called the Houben-Hoesch reaction (eq 22). The Leuckart amide s)oithesis generates aryl amides from isocyanates (eq 23). ... 

A review describes the asymmetric epoxidation of allylic alcohols,369 another the role of metal oporphyrins in oxidation reactions.370 jhe TiiOPrMi, catalysed self-epoxidation of allylic peroxides proceeds via an intermolecular mechanism.371 Racemic allyl alcohols can be resolved by asymmetric epoxidation (eq.35).372 a Pd(II)/Mn02/benzoquinone system catalyses the oxidative ring-closure of 1,5-hexadienes (eq.36).373 propenyl phenols are oxidatively degraded to aryl aldehydes and MeCHO in the presence of Co Schiff-base catalysts.374 An Oppenauer-type oxidation with Cp2ZrH2/cyclohexanone converts primary alcohols selectively into aldehydes.375 co macrocycles catalyse the oxidation of aryl liydrazones to diazo compounds in high yields.376 similar Co complexes under CO oxidise primary amines to azo compounds.377 Arene Os complexes in the presence of base convert aldehydes and water slowly into carboxylic acids and H2.378... 

Scheme 8.121 Synthesis of xanthone derivatives via ortho-acylation of phenols with aryl aldehydes.

In a synthesis of decinine a phenol was protected as a methanesulfonate that was stable during an Ullman coupling reaction and during condensation, catalyzed by calcium hydroxide, of an amine with an aldehyde. Aryl methanesulfonates are cleaved by warm sodium hydroxide solution. " ... 

Aromatic nitro compounds are often strongly colored. They frequently produce characteristic, colored, quinoid derivatives on reaction with alkali or compounds with reactive methylene groups. Reduction to primary aryl amines followed by diazotization and coupling with phenols yields azo dyestuffs. Aryl amines can also react with aldehydes with formation of Schiff s bases to yield azomethines. 

In Figure 13.2, the intensity of the ion at m/z 170 represents a molecular ion of an aromatic compound. The characteristic losses from the molecular ion (M - 1, M - 28, and M - 29) suggest an aromatic aldehyde, phenol, or aryl ether. The molecular formula of Ci2H 0O is suggested by the molecular ion at m/z 170, which can be either a biphenyl ether or a phenylphenol. The simplest test to confirm the structure is to prepare a TMS derivative, even though m/z 11 strongly indicates the diaryl ether. 

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