Arenes formylation

Benzene and naphthalene compounds can be formylated under Vil-smeir conditions. The formyl compounds, with or without isolating, can be condensed with amino arenes to give leuco compounds. In this reaction, the benzhydrol intermediate is not isolated.21,79,84 86 The reaction is generally carried out in an alcohol solvent such as isopropanol, butanol, or pentanol and an acid catalyst such as hydrochloric acid, sulfuric acid, or methanesul-fonic acid.87 Acetic acid can also be used both as catalyst and as the solvent. Urea sometimes is added as catalyst.84,88 Terephthaldehyde reacts with W-diethyl-3-methylaniline89 and substituted azulenes to give a bis-triphenylmethane21 57 and 58, respectively. 

H. S. I. Chao, G. A. Berchtold, Aromatization of Arene 1,2-Oxides. Comparison of the Aromatization Pathways of 1-Carboxy-, 1-Carbomethoxy-, 1-Formyl-, l-(Hydroxyme-thyl)-, and l-(2-Hydroxy-2-propyl)benzene Oxide ,./. Am. Chem. Soc. 1981,103, 898 -902. 

Formylation of arenes using carbon monoxide and hydrogen chloride in the presence of aluminum chloride under high pressure. 

Problem 15.12 Can formylation of an arene, ArH, with an acid chloride be employed to prepare ArCHO ... 

Arenes can be formylated by generating the active intermediate, CfeC—H, from reagents other than HCOCl. The Gatterman-Koch reaction uses a high-pressure gaseous mixture of CO and HCl. 

Regioselective formylation of toluene, meta- and para-xylene, and mesitylene has been achieved by carbonylation in triflic acid at CO pressures of90-125 atm. However, the use of six- to sevenfold excess of acid over arene is required to obtain high yields of the aldehydes 422 Recently, apara-tolualdehyde yield of 99.1 % has been reported (triflic acid/toluene molar ratio = 20, CO pressure = 70 atm, room temperature, 30 min).444... 

Aromatic aldehydes. Acetone cyanohydrin can be used in place of hydrogen cyanide in the Gattermann reaction for formylation of arenes.1 Example ... 

The Vilsmeier Reaction allows the formylation of electron-rich arenes. 

The Vilsmeier-Haack reaction (herein, Vilsmeier reaction ) provides an effective method for the formylation of aromatic systems. The combination of phosphoryl chloride with V-methylaniline or dimethylformamide generates an iminium phosphorus derivative or chloro-iminium cation that is the active electrophile in an electrophilic substitution reaction. The resulting substitution product is an iminium salt 1, which is hydrolyzed on workup with alkali to give the carbaldehyde product 2 (Scheme l).1,2 The method is particularly useful with activated arenes or electron-rich heterocycles, such as pyrroles, furans, thiophenes, and indoles. We had a special interest in the preparation of indole-7-carbal-dehydes, namely, their properties as isosteres of salicylaldehyde. Thus, we became involved in a wide-ranging investigation of 4,6-dimethoxy-... 

Formylation of arenes (1, 220 2, 120). Yields in this reaction can be improved by addition of the arene to a mixture of the ether (25% excess) and stannic chloride (2cquiv.). This inverse addition decreases formation of by-products of the type... 

The electrophilic formylation of arenes with CO in the presence of acids (Gatterman-Koch conditions) is an efficient method for preparing aromatic aldehydes. HF-SbFs-SO2CIF is the most active system for this reaction [82]. It has been demonstrated that even diformylation can be achieved on polymeric aromatics such as biphenyl with the use of fluoroantimonic acid (Eq. 36) [83]. 

Organometallics bearing two heteroatomic moieties on their carbanionic center have found an important place in organic synthesis since the first report of Arens. In particular, they have played a crucial role as formyl or acyl anion equivalents. " " ... 

The mechanism of aromatization of arene 1,2-oxides was studied using a series of model compounds such as 1-carboxy-, 1-carbomethoxy-, 1-formyl- and 1-(hydroxymethyllben-zene oxides. The results obtained support the literature suggestions that arene 1,2-oxides may be intermediates in hydroxylation reactions of biological systems . ... 

Diagram 1 is given to illustrate this description, as well as the following "recipe " "The required tetracarboxylic acid 1 was prepared by alkylation of calix[4]arene ( -butyl bromide, NaH) followed by formylation (CI2CHOCHV TiCy and oxidation (NaCl02, H2NSO3H) " (p. 2681). 

Tab. 5 Formyl-arene aus Arenen bzw. Arylsulfanen mit Alkoxy-dichlor-methanen...

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