Benzenepentamine – Its Easy Accessibility and Use in Syntheses of Pyrazinoquinoxalines

Abstract

Bcnncncpentarnine (6) has been rediscoverud alter about 60 years. A sirnplc and very emcient synthctic route is described which yiclds the very sensitive, colourless 6 in mcthanolic solution in ncarly quantitative yield. Condcnsations or 6 with two masked forms A and B of glyoxal convenicntly lead to two typcs or amino-substih~ted pyra7.inoquinoxalincs. onc with an nngular phcnmthrcnc-type ropology (7a). or one with thc linear anthraccnc-typc structure @a), respectively. with avccptable yields. The r-tiiketone b e n d also reacts with 6, bu1 lcss wleclively. forming thc corresponding terraphenyl derivatives 7b an 8b ol both these hcicrcrtricyclic ring systems. Thc hcretolore unknown nitrobenzenepcntaminc (9). forrncd in addition to bcnzcnehexamine in rcduction rcactions of I.3.5-trinitrobcnxcnctriamine, has also h e n obtained. Based on spectroscopic data, the structures of these two multiamines have been deduced From their condensation products with n-diketones, in the case of the ncw penpamine 9 From its first derivatives 7c -e of pyrazino[2.3~~quinoxaliuv.Benzenehexamine having been studied2-6) very rarely in the past and neglected for almost 50 years is now readily acce~sible'~~) by Birch reduction of 1,3,5-trinitrobenzenetriamine. Previous work from both our laboratorie~~-~) has shown that benzenehexamine can be condensed with various a-diketones*-') and also with masked forms of glyoxa12) (e.g. A*) and B9)) to give numerous derivatives of dipyrazino[2,3-f2',3'-h]quinoxaline(1,4,5,8,9,12-hexaazatriphenylene) 2-4,10) or its parent heteroring system2), respectively, in good yields. This approach proved to be a considerable improvement over an earlier, long, and inefficient 10-step synthesis of the parent dipyrazinoquinoxaline and makes this interesting tetracyclic molecule now readily available for further studies as a ligand for transition metals and as a fundamental building block for compounds with either noncalamitic liquid-crystalline or potential ferromagnetic properties.On the other hand, benzenepentamine (6), the foregoing member of this series of multiamines, has been mentioned 12), prepared from 1,3,5-trinitrobenzenediamine (3) by reduction with tin in hydrochloric acidI3), and even applied to first condensation reactions 13) with carbonyl compounds already in the last century14). With the exception of another synthesis of 6 in which 3 has been reduced with the ' ' Deceased on November 30. 1988. hazardous phenylhydrazine exactly 60 years ago"), 6 was completely forgotten. Our work on N-heterocycles drew our attention also to this interesting multiamine 6 since it should, for instance, allow simple one-pot syntheses of a variety of amino-substituted tetraaza multicyclic aromatic compounds of manifold interest. It was thus necessary to develop a more efficient synthesis of benzenepentamine (6), which indeed could be realized on the basis of the experience gained during our former work on benzenehexamine 2-s,10!The best way to get to benzenepentamine (6) is outlined in Scheme 1. It starts from commercia...

Synthesis of Ru(ii) and Os(ii) photosensitizers bearing one 9,10-diamino-1,4,5,8-tetraazaphenanthrene scaffold

“…1). [68][69][70][71][72][73] First a condensation of 4-nitro-1,2-diaminobenzene and glyoxal in refluxing ethanol was performed to obtain the corresponding 6-nitroquinoxaline in 80% yield. Vicarious nucleophilic substitution with hydroxylamine using sodium methanolate yielded 5-amino-6nitroquinoxaline in a 56% yield, which was then reduced using hydrazine hydrate with 10% Pd/C to yield 5,6-diaminoquinoxaline in 98% yield.…”

“…1). [68][69][70][71][72][73] The 1,4,5,8-tetraazaphenanthrene (TAP) offers similar redox potential as the prototypical 2,2′-bipyrazine ligand while the inclusion of the diamino functionality would allow for the straightforward development of a series of bridging ligands, through condensation with o-diones, such as 1,10-phenanthroline-5,6-dione, for example. We found that 9,10-diNH 2 -1,4,5,8-tetraazaphenanthrene could be directly chelated onto Os(II) centres but that, with Ru(II), the chelation efficiency strongly depended on the ancillary ligands.…”

Redetermination of 1,3,5-trichloro-2,4-dinitrobenzene

“…Indeed, careful study of the kinetics of nitration of 1,3,5-trichlorobenzene to give both the title compound and 1,3,5-trichloro-2,4,6-trinitrobenzene has been carried out (Moodie et al, 1985) and revealed that the title compound is an intermediate in the formation of the trinitro product. Our interest stemmed from the knowledge that 1,3,5-trichloro-2,4,6-trinitrobenzene may be converted to hexaaminobenzene and subsequently to a variety of substituted hexaazatriphenylenes and pyrazinoquinoxalines (Praefcke et al, 1989;Rodgers, 1986;Kohne & Praefcke, 1985). During the course of synthesizing 1,3,5-trichloro-2,4,6-trinitrobenzene, we isolated colourless crystals of the title intermediate compound.…”