Aromatic nucleophilic substitution of hydrogen: mechanism of reaction of 6-nitroquinoline with cyanide ions, with and without participation of methyl cyanoacetate

The mechanism of nucleophilic substitution of hydrogen (SNArH) in 6-nitroquinoline 1 by action of cyanide ion in the presence or in the absence of methyl cyanoacetate in dimethyl sulfoxide has been studied by means of 1H NMR. The main reaction products and some side products have been identified and their time–concentration dependences have been determined. An experiment with 13C enriched potassium cyanide proved that the cyano group replaces hydrogen at the 5-position of the starting compound 1. The two main products obtained from the reaction mixture of 6-nitroquinoline 1 and potassium cyanide are 6-hydroxyquinoline-5-carbonitrile 11 and 6,6′-azoquinoline-5,5′-dicarbonitrile 13. On the basis of the data obtained, a mechanism has been suggested for aromatic nucleophilic substitution of hydrogen by cyanide ion in 6-nitroquinoline 1 involving a Meisenheimer adduct of 6-nitroquinoline 1 with cyanide ion and 6-nitrosoquinoline-5-carbonitrile 14 as unstable intermediates.