Aromatic hydroxy aldehyde

The reaction of trichloro-acetaldehyde (chloral) with phenols under base catalysis leads to p-hydroxyaryltrichloroethanols together with some o-isomer. The corresponding aromatic hydroxy aldehydes are produced after reaction with aqueous alkali or boiling in... 

The product is a P-hydroxy aldehyde (called an aldol) or ketone, which in some cases is dehydrated during the course of the reaction. Even if the dehydration is not spontaneous, it can usually be done easily, since the new double bond is in conjugation with the C=0 bond so that this is a method of preparing a,P-unsaturated aldehydes and ketones as well as P-hydroxy aldehydes and ketones. The entire reaction is an equilibrium (including the dehydration step), and a,P-unsaturated and P-hydroxy aldehydes and ketones can be cleaved by treatment with OH (the retrograde aldol reaction). There is evidence that an SET mechanism can intervene when the substrate is an aromatic ketone. ... 

It can be assumed that, in the presence of InCl3 and water, the cyclic enol ethers 2-618 form a hydroxy aldehyde which reacts with the aniline to give an aromatic im-inium ion. This represents an electron-poor 1,3-butadiene which can undergo a hetero-Diels-Alder reaction [323] with another molecule of 2-618 to give a mixture of the diastereomeric tetrahydroquinolines 2-619 and 2-620. 

Deuterium isotope effects on 15N chemical shift in CDC13 solution as well as in solid state were measured for a series of symmetrical and unsymmetrical di-Schiff bases being derivatives of fra s-l,2-diaminocy-clohexane and various aromatic ort/io-hydroxy-aldehydes [22],57 The AN (D) value determined in solid state for symmetrical di-Schiff base which was a derivative of salicylaldehyde was —1.8 ppm, which was typical of... 

This method has an analogy in the well known acyloin condensation, a reaction which takes place between two molecules of an aromatic aldehyde in a solution containing an alkali cyanide. Thus for example, benzaldehyde gives rise to benzoin, a compound in which the enediolic system, —C(OH)=C(OH)—, exists mainly in the ketonic form —CO—CHOH—. If a hydroxy aldehyde like D-glucose (X) is allowed to... 

LA represents Lewis acid in the catalyst, and M represents Bren sled base. In Scheme 8-49, Bronsted base functionality in the hetero-bimetalic chiral catalyst I can deprotonate a ketone to produce the corresponding enolate II, while at the same time the Lewis acid functionality activates an aldehyde to give intermediate III. Intramolecular aldol reaction then proceeds in a chelation-controlled manner to give //-keto metal alkoxide IV. Proton exchange between the metal alkoxide moiety and an aromatic hydroxy proton or an a-proton of a ketone leads to the production of an optically active aldol product and the regeneration of the catalyst I, thus finishing the catalytic cycle. 

Periodic acid oxidation will also act on a-hydroxy aldehydes and ketones, a-diketones, a-keto aldehydes, and glyoxal. If the two neighboring hydroxyl groups are on an aromatic ring, the carbon-carbon bond is not cleave but the reactant is still oxidized. Thus, catechol is oxidized to the corresponding quinone. 

The analogues of serine and tyrosine were prepared from suitably protected hydroxy aldehydes and the tryptophan analogue from indolepyruvic acid. A wide selection of other o -aminophosphonous acids was also prepared from aliphatic, aromatic and heterocyclic aldehydes and aliphatic ketones. 

Phosphorylated ketenes react with aromatic ortho -hydroxy aldehydes to form coumarins by the Wittig -Horner - type reaction. 

Enantioselective cross aldol reactions. A 3-acylthiazolidine-2-thione can be used as an equivalent of an aldehyde or carboxylic arid in cross aldol reactions to provide p-hydroxy aldehydes or carboxylic acids. The tin enolates formed from Sn(OTf), react with aromatic and aliphatic aldehydes with high svn-selectivity (equation I),... 

The P-acetoxy esters 2 were obtained in yields over the range 69-75%, based on the aldehyde and with a high enantiomer excess (ee). In addition, in this case the absence of a base as a co-catalyst is essential in order to avoid retro-aldol reaction of the product. The scope of this methodology is not restricted to aromatic hydroxy acids, as the non-aromatic cyclohexyl analog was also successfidly deracemized (Scheme 13.3). 

A new method for the ortho hydroxylation of aromatic aldehydes via orrho-lithiated arcnnatic aminoal-koxides has recently been reported by Einhom et al Fonnation of the aminoalkoxide serves two purposes. Firstly, the aldehyde group is protected and, secondly, the aminoalkoxide directs lithiation to the ortho position. Oxidation of the lithio species was effected by either MoOPH or molecular oxygen, albeit in poor yield. Alternatively, a two-step, one-pot condensation of the lithio intermediate with tributyl borate followed by oxidation with hydrogen peroxide gave the ortho-hydroxy aldehydes (24) in slightly better yields (Scheme 9). 

Weller and Wolf (44) investigated a great number of azines, derived from aromatic o-hydroxy aldehydes and o-hydroxy-ketones. 

V. N. Komissarov, V A. Kharlanov, L. Yu. Ukhin, E. Yu. Bulgarevich, and VI. Minkin, Photo-and thermochromic Mannich bases. Derivatives of 2,6-di-fert-butylphenol and aromatic ortho-hydroxy aldehydes, Zh. Org. Khim. 28,513-517 (1992). 

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