Chemical and electrochemical reduction of pyrazino[2,3-g]quinoxalines and of their benzo and dibenzo derivatives; the structure of fluorindine and the formation of tetraanion

• Published in: Canadian journal of chemistry Vol. 65; no. 7; pp. 1619 - 1623
• Main Authors: Armand, Joseph, Boulares, Line, Bellec, Christian, Pinson, Jean
• Format: Journal Article
• Language: English
• Published: Ottawa, Canada NRC Research Press 01.07.1987; National Research Council of Canada
• Subjects: Chemistry; Exact sciences and technology; Heterocyclic compounds; Heterocyclic compounds with several n hetero atoms in the same ring, in separated rings or in fused rings; Organic chemistry; Preparations and properties; Pentacyclic compound; Chemical reduction; Cyclic voltammetry; Nitrogen heterocycle; Aromatic compound; Tricyclic compound; Electrochemical reaction; NMR spectrum
• ISSN: 0008-4042; 1480-3291
• DOI: 10.1139/v87-271

The structure of fluorindine is established by nmr as the 5,14-dihydroquinoxalino[2,3-b]phenazine. The catalytic hydrogenation of 2,3-di(p-methoxyphenyl)pyrazino[2,3-b]phenazine 2 a leads to the 6,11-dihydro derivative 4 a. The electrochemical reduction in an hydroorganic medium furnishes 4 a and then the 1,4,6,11-tetrahydro derivative 8 a. In dry DMSO the voltammogram shows four monoelectronic reversible systems corresponding to the successive formation of a radical anion, dianion, radical trianion, and tetraanion. Thus 2 a appears as a new example of the very restricted class of compounds leading to tetraanions upon electrochemical reduction. The catalytic hydrogenation of 2,7-diphenylpyrazino[2,3-g]quinoxaline 1 a or the reaction of LiAlH 4 with 1,2,7,8-tetramethylpyrazino[2,3-g]quinoxaline 1 b leads to 1,2,3,4-tetrahydro compounds. The electrochemical reduction of 1 a and 1 b in hydroorganic medium leads successively to 1,4-dihydro and then to 1,4,6,9-tetrahydro compounds which undergo a further rearrangement. In dry DMSO 1 a and 1 b behave differently from 2 a: one only observes two reversible monoelectronic systems.