Quinoline 4- methyl-, radical substitution

It is important to note that sodium methylate initiates only the formation of 4-phenylthio-wo-quinoline the product of the competing substitution, 4-methoxy-Ao-quino-line, is produced only in traces. The methylate ion, however, converts a part of the iso-quinoline CT-radicals into the unsubstituted iso-quinoline and produces formaldehyde. 

Zoltewicz and Oestreich (1973) employed sodium methylate to accelerate the reaction between 4-bromo-iso-quinoline and sodium thiophenolate. In this case, the CHjO ion acts as a competing electron donor with respect to the PhS ion. On electron transfer to the substrate, thiophenolate converts into the phenylthiyl radical and then to diphenyldisulhde. Diphenyldisulfide is inactive in further transformations. The methylate ions generate the anion-radicals of the substrate, thus preserving the greater part of the thiophenolate for use in substitution. The observed rate of thioarylation and the yield of 4-phenylthio-iso-quinoline increase in the presence of sodium methylate. Azobenzene inhibits the action of sodium methylate. Scheme 5.7 summarizes what has been mentioned. 

To correlate the two series of substituted pyridines and quinolines, relative rates of alkylation were determined also with 2- and 4-substituted quinolines. The following sequence of nucleophilicity of alkyl and acyl radicals was obtained methyl < primary alkyl < acetyl < i-chlorobenzoyl < -chlorobenzoyl < m-methoxybenzoyl < benzoyl < -methylbenzoyl < -methoxybenzoyl < sec. alkyl < f-alkyl < benzyl. 

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