Reduction of hydrazones of aromatic carbonyl compounds in aprotic media

Hydrazones of aromatic carbonyl compounds of the type ArRC=N-NR'R '', where R, R' and R '' are carbon substituents, are reduced in aprotic media to the radical anion, which may cleave to an amine anion and an imine radical; the reduction is analogous to the reduction of vinyl halides of the type ArR=CR'X. For R' and R '' equal to methyl the rate of cleavage is a linear function of the reversible reduction potential of the hydrazone. When R is hydrogen and R' and R '' are carbon substituents the base generated in the reduction (EGB) may induce an elimination of an amine with formation of a nitrile, when the leaving amine anion is a good leaving group; an analogous elimination to an acetylenic compound is found during the reduction of vinyl halides ArCH=CR'X. When R' is hydrogen the hydrazone may be sufficiently acidic to protonate the radical anion ('father/son' reaction); this is especially found when R '' is an electron attracting group such as benzoyl. For phenylhydrazones, bases generated during the further reduction of the cleavage products may deprotonate the parent. (C) 1997 Elsevier Science S.A.