Electrochemical reduction of di-Schiff bases. Synthesis of piperazines, indoloindoles, diazepines, and diazocines

Abstract

The electrochemical reduction of a series of di-Schiff bases has led to examples where products representing reduction, cyclization, and transannular cyclization are found. Useful synthetic pathways for piperazines, indoloindoles, diazepines, and diazocines are described.

Facile Redox Interconversion of 6,11‐Diphenyldibenzo[b,f][1,4]diazocine and 2‐(2‐Aminophenyl)‐1,3‐diphenylisoindole: Reversible SET Ring Contraction and Expansion Processes

“…The subsequently obtained X-ray diffraction and 13 C NMR spectroscopic data unequivocably established the 3D-structure of 6 as that rendered in Scheme 2, with coplanarity of the transannular C=N and N=C groups and with the cross-ring N 5 and N 11 atom separations of 3.294(3) Å and the C 6 and C 12 atom separation of 3.000(2) Å. The cross-ring proximity of these atoms raises the probability of transannular bonding in radicalanionic or dianionic intermediates (i.e., 7a to 8) in SET processes (Scheme 2).…”

“…In order to avoid the destabilizing ortho-H repulsions in 2 (bracketed by arrows), we then examined the electrontransfer reduction of an isomer of 1, namely, 6,12-diphenyldibenzo[]b,f [1,5]diazocine (6) (Scheme 2).…”

“…[4b] Although the validity of structure 6 was assured both by its logical synthesis via the bimolecular dehydration of 2-aminobenzophenone and by its limited spectroscopic data, [5] its 3D stereochemistry was not. The subsequently obtained X-ray diffraction and 13 C NMR spectroscopic data unequivocably established the 3D-structure of 6 as that rendered in Scheme 2, with coplanarity of the transannular C=N and N=C groups and with the cross-ring N 5 and N 11 atom separations of 3.294(3) Å and the C 6 and C 12 atom separation of 3.000(2) Å.…”

Electrochemical Reduction of 1,2‐Di(p‐tolylimino)ethane and 1,2‐Di(2,4‐dimethylphenylimino)ethane in Dimethylformamide

“…[1][2][3][4][5] However there are few reports dealing with electrosynthetic studies on Schiff bases in the literature. Koch and Dessy 6 have investigated the effect of the solvent and the structure of the Schiff base on the electrochemical reduction of diimines in DMF. The electrochemical studies of a series of hydroxyl substituted Schiff bases, H 2 salen and H 2 salophen 7,8 and their nickel complexes 9 have also been reported.…”

Investigation of the electrochemical reduction mechanism of 1-[N-(2-pyridyl)aminomethylidene]-2(1H)-naphthalenone (PN)

“…Various studies of the electroreduction of imine groups in nonaqueous media have appeared in the literature [18,19]. Electrochemical reduction of diimines was studied by Koch and Dessy in DMF [20] and by Solak et. al.…”