A. Z. Afanas'ev

Synthesis of isomeric O-(phenylvinyl)-acetophenone oximes and their rearrangement to pyrroles

Methods were developed for the radioselective synthesis of α- and β-O-(phenylvinyl)-acetophenone oximes. Their conversion to 2,5- and 2,4-diphenylpyrroles, respectively, confirms the mechanism of this process, including a step of [3,3]-sigmatropic displacement.

Methods for the synthesis of 3-nitropyridines (review)

The review includes the published data on methods for the synthesis of compounds that contain the 3-nitropyridine skeleton from acyclic synthones and via transformation of other heterocyclic rings.

REACTION OF ALKYL-3-NITROPYRIDINIUM SALTS WITH DIMETHYLFORMAMIDE DIETHYLACETAL

Alkyl-3-nitropyridinium salts react with DMF diethylacetal to give β-aminovinyl derivatives under considerably milder conditions than with the corresponding bases. The regioselectivity of this process has been studied in dependence on the structure and positions of the alkyl substituents in the initial salt.

Indoles from 3-nitropyridinium salts 9. Methyl ethyl ketone N-methylimine in the indolization of 1-methyl-3-nitropyridinium salts

In a study of the direction of the indolization of alkyl-substituted 3-nitropyridinium salts in reaction with methyl ethyl ketone N-methylimine as a function of the structure of the salts, it has been established that in the presence of a substituent at position 4, initial attack at position 6 by the most substituted enamine form of the imine leads to preferential formation of 7-methylindole whereas in its absence the regioselectivity of the process is reduced and in the indole mixture the fraction of 3-methylindole increases.

Synthesis of indoles from pyridinium salts. - 8. Preparation of a free anhydro-base from the 1,2,5,6-tetramethyl-3-nitropyridinium cation, and its involvement in the synthesis of indoles from 3-nitropyridinium salts

The reaction of 1,2,5,6-tetramethyl-3-nitropyridinium perchlorate with acetone and piperidine on a solid carrier has given the novel, relatively stable 3-nitropyridine anhydro-base, 1,2,5-trimethyl-3-nitro-6-methylene-1,6-dihydropyridine, which bears alkyl groups only. This anhydro-base has been shown not to be an intermediate in the synthesis of indoles from 3-nitropyridinium salts.

Synthesis of indoles from pyridinium salts. 7. Sterically hindered alkyl-3-nitropyridinium salts in the synthesis of indoles

The introduction of bulky alkyl substituents (iso-Pr,tert-Bu) into any positions of the starting 3-nitropyridinium salt only increases the reaction time and decreases the yields of the corresponding alkylindoles somewhat.

Synthesis of indoles from pyridinium salts 5. Secondary amines in the reaction of 3-nitropyridinium salts with acetone

The use of secondary amines in the reaction of 3-nitropyridinium salts with acetone makes it possible to isolate stable intermediates in the formation of indoles — (o-N,N-dialkylaminobenzyl)ketones — and to observe new reaction pathways — the formation of bisindolylpropanes and p-nitroanilines.

Synthesis of indoles from pyridinium salts. 6. Reaction of 3-nitroquinolinium salts with ketones in the presence of amines

It is shown that in the reaction of 3-nitroquinolinium salts with aliphatic ketones and amines the ketone adds to the 2 and 4 positions with the formation of tricyclic adducts — benzazabicyclononane derivatives. Their conformational analysis was carried out on the basis of the NMR spectral data. Intermediate products of the monoaddition of ketones in the 4 position of the heteroring were isolated for the unsubstituted 3-nitroquinolinium salt.

Synthesis of indoles from pyridinium salts. 4. Ketimines in the synthesis of indoles from 3-nitropyridinium salts

The possibility of using certain ketimines in place of mixtures of ketone and amine in the synthesis of indoles from 3-nitropyridinium salts has been demonstrated. The use of ketimines leads, in many cases, to increased yields of indoles and simplifies their isolation. It has been established that the rate of indole formation is considerably increased in polar aprotic solvents.

Synthesis of indoles from pyridinium salts. 1. Recyclization of 4-alkyl-2,6-dimethyl-3-nitropyridine methiodides in the presence of ketones

A method for the synthesis of 4-alkylpolymethylindoles by recyclization of 4-alkyl-2,6-dimethyl-3-nitropyridine methiodides in the presence of ketones was developed. A method for establishing the structures of the polyalkylindoles on the basis of data from the PMR spectra and the proton-coupled 13C NMR spectra is proposed.