No abstract

The structure of fluorindine is established by nmr as the 5,14-dihydroquinoxalino[2,3-blphenazine. The catalytic hydrogenation of 2,3-di(p-methoxyphenyl)pyrazino[2,3-b]phenazine 2a leads to the 6,ll-dihydro derivative 4a. The electrochemical reduction in an hydroorganic medium furnishes 4a and then the 1,4,6,11-tetrahydro derivative 8a. 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 2a 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-glquinoxaline l a or the reaction of LiAlH, with 1,2,7,8-tetramethylpyrazino[2,3-g]quinoxaline l b leads to 1,2,3,4-tetrahydro compounds. The electrochemical reduction of l a and 1 bin 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 l a and l b behave differently from 2a: one only observes two reversible monoelectronic systems.JOSEPH ARMAND, LINE BOULARES, CHRISTIAN BELLEC et JEAN PINSON. Can. J. Chem. 65, 1619Chem. 65, (1987.Par rmn on montre que la fluorindine est la dihydro-5,14 quinoxalino [2,3-b] phknazine. Par hydrogtnation catalytique la di(p-methoxypheny1)-2,3 pyrazino [2,3-b] phenazine 2a fournit le dtrivt dihydro-6,11 4a. La rtduction tlectrochimique en milieu hydroorganique foumit 4a puis le dtrivt tttrahydro-1,4,6,11 8a. Dans le DMSO tres sec le voltamogramme montre la prksence de quatre pics monotlectroniques rtversibles correspondant a la rkduction successive en radical anion, dianion, radical trianion et enfin tttraanion : 2a est un nouvel exemple de composts -tres peu nombreux -susceptibles d'engendrer un tttraanion par rtduction tlectrochimique. L'hydrogtnation catalytique de la diphtnyl-2,7 pyrazino [2,3-g] quinoxaline l a ou l'action de AlLiH, dans le cas de la tttramtthyl-1,2,7,8 pyrazino [2,3-g] quinoxaline l b conduit au dtrivt tttrahydro-1,2,3,4. La reduction tlectrochimique en milieu hydroorganique de l a et l b conduisent successivement aux dtrivks dihydro-1,4 puis tetrahydro-1,4,6,9, ce dernier se rtarrangeant. Dans le DMSO tres sec l a et l b ont un comportement difftrent de celui de 2a puisqu'on observe seulement la prtsence de 2 pics mono&lectroniques rtversibles.We have been interested for sometime in the chemical and H H electrochemical reduction of N-heterocyclic compounds (1, 2). We now report the behaviour of pyrazino[2,3-glquinoxalines 1, pyrazino[2,3-blphenazines 2, and quinoxalino[2,3-blphena-"~n~a~x " a:aiD zines 3. Through the examination of such a series of com-R3

JOSEPH ARMAND, LINE BOULARES, KHALED CHEKIR, and CHRISTIAN BELLEC. Can. J . Chem. 59, 3237 (1981). The hydrogenation of 2,3-dimethylpyrazino[2,3-blquinoxaline 1 and 2-phenylpyrazino[2,3-b]quinoxaline 2 leads to the corresponding 5,lO-dihydroderivatives 3b and 4b. LiAlH, reduction of 2, of 2.3-dimethyl-6,7-diphenylpyrazino[2,3-b]pyrazne 8 and 2,6,7-triphenylpyrazino[2,3-blpyrazine 9 furnishes the corresponding 1,2,3,4-tetrahydroderivatives 7,10, and 11. NaBH, reduction of 2 leads to a mixture of 4b and 7. In hydroorganic medium 1 and 2 are electrochemically reduced to 36 and 46 with which they form a redox system. Although the synthesis of pyrazino[2,3-blquin-1). The reduction products of 1 and 2 have two oxalines has been investigated (1) neither their amino protons which are readily exchanged by chemical nor their electrochemical reduction has addition of D,O so that the isomeric structures been studied.shown below have to be considered:We report the hydrogenation, the reduction with LiAlH, and NaBH,, and the electrochemical reduction of compounds 1 and 2. Concerning the electrochemical reduction, the presence of two condensed pyrazine rings made possible two reaction paths, either a reduction into a 1,4-(or 5.10-) dihydro derivative as in the case of pyrazines, or a behaviour similar to that of flavines leading to a 1 3 -(or 4, lo-) dihydro compound. HydrogenationIn the presence of Pd/C, hydrogenation of 1 and 2 leads to the dihydro derivatives 3b and 4b, the structures of which were determined by nmr (Table k I A rapid equilibrium on the nmr time scale of the two tautomers 3c and 3c' cannot be excluded on the grounds of the nmr spectrum. However, acetylation gives a diacetylated compound to which the nmr spectrum permits assigning the 1 ,Cdiacetyl-1 ,4-dihydro structure or the 5,lO-diacetyl-5,lOdihydro structure (see Experimental). Thus, the reduction product of 1 must have a plane of symmetry, which rules out structure 3c. Structures 3a and 3b can be discriminated by examination of the chemical shifts. The aromatic protons of 1,2,3,4-tetrahydrophenazine 5 give evidence of a multiplet

. Can. J. Chem. 60,2797Chem. 60, (1982. We have been interested for some time in the very low solubility in usual solvents (methanol, electrochemical reduction of heterocyclic com-acetonitrile, dimethylsulphoxide, dimethylformapounds with two 1,4-nitrogen atoms in a six-mem-mide). It can be dissolved in hot acetic acid or in bered ring. We now report the electrochemical cold trifluoroacetic acid. Our first attempts aimed reduction in protic and aprotic medium of the at obtaining an unambiguous determination of the 1 quinoxalino[2,3-blquinoxaline, 1. This compound structure by X-ray crystallography, but we were 1 possesses two conjugated unable to obtain suitable crystals from CH3COOH 1 -N=c-c=N-or CF,COOH solutions. An nmr spectrum re-I I corded in CF3COOH shows a single AA'BB' patsystems and it seemed interesting to investigate tern for the eight aromatic protons, which gives no how the conjugation of two systems would indication on the structure of fluoflavine the proinfluence their electrochemical behaviour. A single tons of the benzenic rings being equivalent because study of 1 has been published (1); of the protonation of the nitrogen atoms and the fast however, its conclusions are erroneous. exchange of these protons. As we shall see later on, the electrochemical

. Can. J. Chem. 66, 1500 (1988). The reaction of 2,3-diaminopyridine with the dimeric 4,5-dimethylcyclohexa-3,5-dien-1,2-dione gives 7, 8-dimethylpyrido[2,3-b]quinoxaline, 1, in good yields; in the same way 3,4-diaminopyridine gives the 7,s-dimethylpyrido[3,4-blquinoxaline 2. The electrochemical reduction of 1 and 2 in hydroorganic medium gives the 5,lO-dihydro compounds 6 and 7; 1 and 2 present a single 2e-polarographic wave, in contrast to phenazine which shows two monoelectronic waves. The catalytic hydrogenation of 1 and 2 gives 6 and 7 and does not involve the pyridinic ring as in the case of pyridopyrazines. A1LiH4 does not react with 2 but 1 is reduced into the 1,2-dihydro derivative 8. The behavior of 1 and 2 is thus different from that of pyridopyrazines (which give the 1,2,3,4-tetrahydro compounds) and from that of phenazine (which gives the 5,lO-dihydro derivative). NaBH4 reacts with pyridopyrazines to give, according to the substituents, 1,2-or 5.6-dihydro or 1,2,3,4-tetrahydro derivatives. Methylmagnesium chloride reacts with 1 to give a mixture of 2-methyl-1,2-dihydro, 2,6,7-trimethyl, and 4,6,7-trimethylpyrido[2,3-blquinoxaline. In the case of 2, 4,6,7-trimethylpyrido[3,4-blquinoxaline is obtained.JOSEPH ARMAND, LINE BOULARES, CHRISTIAN BELLEC et JEAN PINSON. Can. J. Chem. 66, 1500 (1988). L'action de la diamino-2,3 pyridine sur la dimethyl-4,5 cyclohexadikne-3,5 dione-1,2 sous forme dimkre fournit avec un bon rendement la dimethyl-7,8 pyrido[2,3-blquinoxaline 1. En utilisant la diamino-3,4 pyridine on obtient la dimethyl-7,8 pyrido[3,4-blquinoxaline 2. En milieu hydroorganique la reduction Clectrochimique de 1 et 2 foumit les derives dihydro-5,10 : 6 et 7; 1 et 2 presentent une seule vague polarographique de 2e-contrairement i la phtnazine qui donne deux vagues monoClectroniques. L'hydrogknation catalytique de 1 et 2 foumit 6 et 7 et ne conceme donc pas le noyau pyridine comme dans le cas des pyridopyrazines. A1LiH4 est sans action sur 2 alors que 1 fournit le derive dihydro-1,2 : 8; le comportement de 1 et 2 diffkre de celui des pyridopyrazines (qui donnent des derives tetrahydro-1,2,3,4) et de la phknazine (qui foumit le derive dihydro-5,lO). Avec NaBH4 1 fournit un melange de 6 et 8 tandis que 2 donne le derive tetrahydro-1,2,3,4. L'action de NaBH4 sur les pyridopyrazines a kt6 egalement 6tudiCe : selon la nature du substituant des derives dihydro-1,2, tetrahydro-1,2,3,4 ou dihydro-5,6 sont obtenus. Le chlorure de m&thylmagntsium conduit dans le cas de 1 i un melange de derive dihydro-1,2 methyl-2, de trimethyl-2,6,7 pyrido with 2-formyl-3 -aminoquinoxaline (4). The few pyrido [3,4-b]quinoxalines which are known have been obtained by cyclization of 3-amino-4-(2-aminoani1ino)pyridine (5) or of 3-amino-4-(2-aminoto1uidino)pyridine (3). In view of the rather low yields and the complicated experiments, we looked for alternative routes to prepare these compounds. W e reacted 2,3-and 3,4-diaminopyridine with a quinone: 4,5-dimethylcyclohexa-3,5-dien-1,2-dione. When the quinone is used as a monomer, ...