REACTION OF AMINOPROPANEDINITRILE 4-METHYLBENZENESULFONATE [AMINOMALONONITRILE PARA-TOLUENESULFONATE (TOSYLATE)] WITH AROMATIC-ALDEHYDES

Aminopropanedinitrile 4-methylbenzenesulfonate (ammoniopropanedinitrile p-toluenesulfonate, aminomalononitrile p-toluenesulfonate (tosylate), 1) reacts with aromatic aldehydes in methanolic sodium ethanoate to give diastereoselectively (E,E)-4-amino-1-aryl-3-cyano-4-methoxy-2-aza-1,3-butadienes (3) and trans-3,6-diaryl-2,2,5,5-tetracyanopiperazines (4). The product distribution (3:4) depends on the ratio of reactants and the structures of the substrates. Electron-releasing groups on the 4-position of the phenyl ring favor piperazine (4) formation (method B.) The formation of piperazines (4) may involve synthetically useful N-protonated aryl-and cyano-stabilized azomethine ylide (prototropic 1,3-dipoles) intermediates which could have resulted from an imine-azomethine ylide tautomerism of prior formed 1-aryl-3,3-dicyano-2-aza-1-propenes. 1,3-Dipolar cycloaddition [4 + 2] reactions of the highly reactive azomethine ylides with dimethyl 1,2-ethynedicarboxylate (DMAD) give 3,4-dicarbomethoxy-2-cyano-5-aryl-3-pyrrolines, which undergo facile dehydrocyanation to 3,4-dicarbomethoxy-2-cyano-5-arylpyrroles. The possible intermediacy of ketenimines and of aryl- and cyano-stabilized 2-azaallyl anionic intermediates in equilibrium with azomethine ylides is also considered.