Formamides reaction with aromatic compounds

The reaction of formamide with aromatic compounds under ultraviolet irradiation is still unexplored and only preliminary results have so far been obtained. In the cases already studied it has been found that this reaction must be sensitized with a ketonic sensitizer, usually acetone, in order to take place. The mechanism of the photoamidation of aromatic compounds certainly differs from the one of simple olefins. The detailed mechanism still awaits further experimental evidence, and in some cases involves, most probably, radical combinations and not addition of radical to unsaturated systems. Interactions of the excited sensitizer with aromatic compounds, having in some cases triplet energies similar or just a bit higher than those of the sensitizers used, must be brought into consideration. Experimentally it has been shown that the photosensitized amidation of benzene leads to benzamide (11),... 

Sometimes, the exchange does not work well under reflux conditions. A few alternatives are the use of phase transfer catalysts (ammonium or phosphonium salts), crown ethers, or exchange in melts or under solid-state conditions (Apparu and Madelmont, 1998). Melts are either the substrate itself at its melting point (where it has to be stable, and must have a high dielectric constant to solubilize Na I), a melt of acetamide or formamide, or ammonium sulfate below its melting point (reaction at 120—160°C). This technique is mostly used with aromatic compounds (Seevers and Counsell, 1982). 

Aromatic and heterocycHc compounds are formylated by reaction with dialkyl- or alkylarylformamides in the presence of phosphoms oxychloride or phosgene (Vilsmeier aldehyde synthesis) (125). The Vilsmeier reaction is a Friedel-Crafts type formylation (126), since the intermediate cation formed by the interaction of phosphoms oxychloride with formamide is a typical electrophilic reagent. Ionic addition compounds of formamide with phosgene or phosphoms oxychloride are also known (127). 

Low molecular weight aromatic ethers have been prepared principally by the condensation of phenolate salts with aromatic halides 82). The Ullmann condensation (81), which employs copper or its salts as catalysts has been used in most cases in the laboratory. Recently a modification of the Ullmann condensation which consists of heating copper (1) oxide, the free phenol, and the aromatic halide in s-collidine has been reported (3). This method is recommended for alkali-sensitive aromatic compounds. In addition, reaction of phenolate salts with copper (1) oxide and the aromatic halide in boiling N,N-dimethyl formamide is described. When the halogen is activated by electronegative groups as in -chloroni-... 

It thermally decomposes to A -dimethylcarbamoyl chloride. Secondary formamides form similar adducts, which on heating afford isocyanates. Aromatic compounds such as anisole are not foimylated by the DMF-SO2CI2 adduct but chlorosulfonated. This reaction was also performed with thiophenes 2-thiophenecarbaldehydes are formed as byproducts. The formation of triformaminomethane from form-amide and SO2CI2 has been reported. ... 

Fluorinated aromatic compounds. Finger and Kruse found that an aromatic chlorine or bromine atom activated by an o- or p-nitro group is subject to nucleophilic displacement by fluoride ipn on reaction with potassium fluoride in solvents such as succinonitrile, dimethyl formamide, or dimethyl sulfoxide. Unpublished work at Olin Mathieson Chemical Corporation indicates that best results are obtained with dimethyl sulfoxide as solvent and with potassium fluoride that has been finely ground (<100 mesh) and dried in a vacuum oven at 100° for at least 4 hrs. prior to use. In a typical case a mixture of p-nitrochlorobenzene, potassium fluoride, and dimethyl sulfoxide is stirred under reflux at 180° for 8-9 hrs., the cooled mixture... 

A variation of the Vilsmeier-Haack reaction uses a formamide such as 211 with benzene (or another aromatic compound) to give the aromatic aldehyde (benzaldehyde) and the amine precursor to the formamide (N-methylaniline in this case). A solvent-free Vilsmeier reaction has been reported using microwave irradiation on silica gel. 39... 

Imidazoles.—Formation. Several new syntheses of imidazoles from isocyanides have been reported these include the formation of 1-alkyl-imidazoles (396) by the action of primary amines on 2-isocyano-2-tosylstyrene, PhCH=C-(NOTos, the cyclization of the enamine Me2NCH=C(NC)C02Me to compound (397) in the presence of methyl iodide,and the preparation of the ethers or thioethers (398) from isocyano-cyanides R CH(NC)CN by their reaction with alcohols or thiols R XH, respectively.Aromatic aldehydes are converted into 2-aryl-4,5-dichloroimidazoles (399) by the combined action of cyanogen and hydrochloric acid. 5-Acetyl-4-methylimidazole (400) results when form-amido-acetylacetone, AC2CHNHCHO, is heated with formamide and formic acid. Exhaustive chlorination of tetramethyldithio-oxamide leads to the tri-chloro-imidazolium cation (401). ... 

The Vilsmeier reaction, whereby amides are converted to highly electrophilic imi-nium ions, which may then react with carbonyl compounds or weakly nucleophilic groups such as aromatic rings, has long been known. Comprehensive reviews on carbonic acid derivatives obtained from formamides are available [1295-1297]. In a wider sense, these derivatives belong to the chemistry of formaldehyde. 

The Vilsmeier-Haack reaction leads to the formation of aromatic aldehydes starting from reactive aromatic compounds. The usual reagent combination is phosphoryl chloride or phosgene together with V-methylformanilide (MFA) or VA -dimethyl-formamide (DMF) [139,140]. First, a V,V-dimethyliminium salt, e.g. 63, is formed which, after basic hydrolysis, gives carbaldehyde. 

Reductions with zinc are carried out in aqueous [160 as well as anhydrous solvents [163 and at different pHs of the medium. The choice of the reaction conditions is very important since entirely different results may be obtained under different conditions. While reduction of aromatic nitro groups in alkali hydroxides or aqueous ammonia gives hydrazo compounds, reduction in aqueous ammonium chloride gives hydroxylamines, and reduction in acidic medium amines (p. 73). Of organic solvents the most efficient seem to be dimethyl formamide [164 and acetic anhydride [755]. However, alcohols have... 

Vilsmeier-Haack reaction. Formulation of activated aromatic or heterocyclic compounds with disubstituted formamides and phosphorus oxychloride. 

Modest amounts, of formamides and/or ureas resulted from reaction of aliphatic and cycloalkyl nitro compounds with Fe(CO)s (Alper, 1972b). Photoreduction of aromatic nitro compounds to nitroso compounds or... 

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