Mechanism for simultaneous reduction of nitro group (into aniline) and aromatic substitution (into benzonitrile) by Ethyl cyanoacetate?
This reaction was conducted using a 3- to 5-fold excess of ethyl cyanoacetate (ECA) and KOH over the arylnitro compounds in dimethylformamide (DMF). It is also important to realize that most KOH is 15% water, which allows for a source of protons in this basic medium. Steps 1 --&gt; 3 (Scheme 1) illustrate a possible route to nitrone 4. In so doing the ECA moiety is being oxidized as the arylnitro compound is being reduced. Addition of hydroxide to nitrone 4 forms 5, which can collapse in two ways. One pathway (another will be mentioned later) leads to reactive ethyl oxocyanoacetate 6 and an aryl hydroxylamine. Base deprotonates the hydroxylamine which adds to 6 to afford species 7 and liberates cyanide anion. Addition of cyanide to the aromatic ring of 7 affords arylamine 8 with loss of the half ester of oxalic acid. A second equivalent of 6 reacts with amine 8 to produce target compound 9. 

Condensation (Scheme 2) of the anion 2 of ECA with ethyl oxocyanoacetate 6 provides ketodiester 10 which condenses with arylamine 8 to form the second targeted product 11. Scheme 3 provides another mode of collapse of intermediate 5 which leads to 9. The hydrolysis of 9 and 11 is routine. There are undoubtedly other variants of these Schemes that may apply.

Update: The reference provided by the OP was not the original paper in the series and the picture provided referred to reference 5. The original[1] reactions with 6-nitroquinoline used KCN as the base providing yields of 9 (IIa) in the 50% range and trace amounts of 11 (IIIa) in reaction times up to 5 hours.  After 24 hours the yield of 9 is greatly reduced with the formation of the oxamic acid derived from ester 9 by an unspecified mechanism of formation. The appearance of 16.5% of 11 should got be construed that 11 is derived from 9. Significantly, the use of KOH as a base produces 9 in 66.5% yield without the formation of 11.


Y. Tomioka, A. Mochiike, J. Himeno and M. Yamazaki, Chem. Pharm. Bull., 1981, 29(5), 1286.