G. P. Gromova

Reactions of aromatic and heteroaromatic compounds bearing electron acceptor substituents

The specificity of the nitration and bromination of dimethyl(2-thienyl)sulfonium salts was studied. It was found that, in contrast to methyl 2-thienyl sulfide, which reacts to form 3- and 5-substituted derivatives, the sulfonium salts give a mixture of 4- and 5-substituted products. Total suppression of the activity of the α position under the influence of the sulfonium grouping is not observed.

Directive nature of the nitration of the oximes of 2-acetylthiophene and 2-propionylthiophene

A method of obtaining pure 2-acetyl- and 2-propionyl-5-nitrothiophenes by nitrating the oximes of the corresponding ketones with the subsequent isolation from the mixtures formed of the pure oximes of the 2-acyl-5-nitrothiophenes and their saponification has been developed. The pure 2-acetyl- and 2-propionyl-4-nitrothiophenes have been isolated by crystallization from the products of the nitration of the corresponding ketones, which form in each case a mixture of the corresponding 2-acyl-4-nitro- and 2-acyl-5-nitrothiophenes containing about 90% of the 4-nitro isomer.

Course of bromination of thiazole and 2-methylthiazole

Bromination of thiazole by bromine in the presence of aluminum chloride in neutral solvent or without solvent takes place at the 2-position. Such an orientation contradicts the traditional addition-cleavage mechanism, and agrees with the ylid mechanism of electrophilic substitution. 2-Methylthiazole brominates at the 5-position, and the reaction is impeded in the presence of aluminum chloride; this is due to heterocycle deactivation by complexation with the Lewis acid at the nitrogen atom.

Reactions of aromatic and heteroaromatic compounds bearing electron-acceptor substituents: X. Alkylation and acylation of furfural

A mixture of products of mono- and polyalkylation is formed in the isopropylation of furfural in chloroform in the presence of excess aluminum chloride. The acetylation of furfural under such conditions gives only 5-acetylfurfural, the formation of which probably proceeds through the intermediate addition of acetyl chloride to the carbonyl group of furfural.

Reactions of aromatic and heteroaromatic compounds carrying electron acceptor substituents

1. The bromination of a complex of acetophenone with aluminum chloride with the formation of m-bromoacetophenone, contrary to the literature data, can be carried out successfully in a suitable solvent (dichloroethane, chloroform), and the excess of aluminum oxide sufficient for the reaction can be reduced to 0.5 mole, instead of 1.5 moles in work without a solvent. 2. The dissociation of the complex observed when the dilution is increased or the solvent is replaced, leads to the formation of phenacyl bromide, the product of bromination of the side chain.

Reactions of aromatic and heteroaromatic compounds containing electron-acceptor substituents

Synthetic methods based on accessible furan compounds of 5-benzyl(3-furyl)carbinol, a necessary component for the preparation of modified pyrethrins, were studied. The carbinol was obtained in 24% overall yield by a five-step synthesis starting from 4-bromofuran-2-carboxylic acid, for the preparation of which an improved method is proposed. Acylation of benzene with the chloride of the latter acid gave 4-bromo-2-benzoylfuran (in 77% yield), the reduction of which by the action of AlCl3 + LiAlH4 gave 4-bromo-2-benzylfuran (in 74% yield). The latter was treated with butyllithium and dimethylformamide to give 5-benzyl-3-formylfuran, which was converted to the carbinol in quantitative yield by the action of LiAlH4.