Formylation of aromatic compounds

Titanium(rV) Lewis Acids 731 Table 17. Formylation of aromatic compounds with (MeO)CHCl2 and TiC. ... 

PPA has been used for the formylation of aromatic compounds with hexamethylenetetramine yields are not high, but the method is simple. ... 

Carbon monoxide and formic derivatives can also be used to make formylations of aromatic compounds (ref. 4) in acidic or superacidic medium. 

This reaction has general applications in the formylation of aromatic compounds. 

Acetone cyanhydrin and aluminium chloride may be used in place of hydrogen cyanide in the Gattermann formylation of aromatic compounds. Yields and substrate reactivities are comparable to those observed with the Gattermann procedure. The trimethylstannyl groups in stannyl-pyridines and -quinolines may be replaced regiospecifically by acyl groups by reaction with acyl chlorides. When the tin substituent is not at the 2-position, palladium catalysis is necessary, but this also leads to a small amount of formation of a bipyridyl [equation (10)1. 

Formylation of aromatic compounds such as benzene, toluene, xylenes, mesitylene, indan, tetralin, fluoro- chloro- and bromobenzene in HSOsF-SbFs under atmospheric CO pressure at 0°C was achieved in high yields (SubstrateiHSOsFiSbFs mol ratio of 20 174 138). Linder reduced molar ratios of SbFs HS03F both formylation and sulfonation take place. 

Table 2.3 CO formylation of aromatic compounds using various Lewis- and Bronsted acids as catalysts...

CARBON MONOXIDE AS REAGENT IN THE FORMYLATION OF AROMATIC COMPOUNDS... 

Targeted products include para-anisaldehyde, ortho- and para-hydroxybenzaldehyde which are important intermediates for the manufacture of chemicals used in the flavor and fragrance market and various other chemicals. The use of CO technology (HF/BF3) to produce these aldehydes in a two-step process from phenol as reagent is economically attractive due to the relative low cost and other benefits associated with syngas as reagent. The aim of the study was to evaluate and understand this relatively unexplored approach to the formylation of aromatic compounds. 

While the Friedel-Crafts acylation is a general method for the preparation of aryl ketones, and of wide scope, there is no equivalently versatile reaction for the preparation of aryl aldehydes. There are various formylation procedures known, each of limited scope. In addition to the reactions outlined above, there is the Vdsmeier reaction, the Reimer-Tiemann reaction, and the Rieche formylation reaction The latter is the reaction of aromatic compounds with 1,1-dichloromethyl ether as formylating agent in the presence of a Lewis acid catalyst. This procedure has recently gained much importance. 

Friedel-Crafts acylation reactions of aromatics are promoted by Tilv complexes.104 In some cases, a catalytic amount of the titanium compound works well (Scheme 28). In addition to acyl halides or acid anhydrides, aldehydes, ketones, and acetals can serve as electrophile equivalents for this reaction.105 The formylation of aromatic substrates in the presence of TiCl4 is known as the Rieche-Gross formylation metalated aromatics or olefins are also formylated under these conditions.106... 

Another commercial aldehyde synthesis is the catalytic dehydrogenation of primary alcohols at high temperature in the presence of a copper or a copper-chromite catalyst. Although there are several other synthetic processes employed, these tend to be smaller scale reactions. For example, acyl halides can be reduced to the aldehyde (Rosemnund reaction) using a palladium-on-barium sulfate catalyst. Formylation of aryl compounds, similar to hydrofomiylation, using HCN and HQ (Gatterman reaction) or carbon monoxide and HQ (Gatterman-Koch reaction) can be used to produce aromatic aldehydes. 

Duff reaction (1, 430). Review. In the clastical procedure highly activated aromatic compounds are converted into their formyl derivatives by treatment with hexamethylenetetramine and glyceroboric acid yields are generally low. Smith finds that a variety of aromatic compounds, including simple hydrocarbons, when treated with hexamethylenetetramine in conjunction with trifluoroacetic acid al reflux temperature (82- 90") arc converted into i mine products which yield aldehydes on hydrolysis ... 

Tanaka, M., Fujiwara, M., Ando, H., Souma, Y. The influence of aromatic compound protonation on the regioselectivity of Gattermann-Koch formylation. Chem. Common. 1996,159-160. 

Reimer-Tiemann reaction The formylation of aromatic rings using CHC13 and OH-. Useful only for phenol, and a few heterocyclic compounds. 

Formylation of aromatics, alkenes, activated H compounds by Me2N+=CHCICI (Vilsmeier-Haack) or Me2N+=CCI2CI (Viehe) reagent (see 1st edition). 

Reactivity First and foremost, porphyrins are aromatic molecules. For example, they undergo some of the electrophilic substitution reactions characteristic of aromatic compounds—nitration, halogenation, sulphona-tion, formylation, acylation, and deuteration. Porph)nins differ from molecules such as benzene, in that there are two different sites on the macrocycle where electrophilic substitution can take place with different reactivities the meso-position and the pyrrole p-position. Which of these... 

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