A new synthetic method for the preparation of polyazaacenes is described starting from two different nucleophilic building blocks. Disubstituted oxalic amidines 1 can be cyclized under mild conditions with 2,3-dichloro-5,6-dicyanopyrazine (3) to yield 5,6-dihydropyrazino[2,3-b]pyrazines 4a-c. By employing higher temperatures and 2 equiv. of 3, octaazanaphthacene 6 can be isolated. Similarly, pyrazino [2,3-b]pyrazines 2 and bielectrophile 3 yielded novel dodecaazahexacenes 8 in addition to semicyclized derivative 9. When tetraazafulva-

Employing three different syntheses a broad spectrum of 4H-imidazoles 3a - 3s has been synthesized. In the course of the two-fold aminolysis reaction leading to derivatives 3q - 3s, deeply colored byproducts could be isolated and structural characterized.These novel donor-acceptor derivatives of type 7 consist of an 1H- and 4H-imidazole which are connected by a nitrogen bridge and rearrange via rapid 1,3-/1,5-hydride shifts. Using 1H NMR experiments the aminolysis product 3p shows prototropic isomers which could be detected in equilibrium for the first time. Cyclovoltammetric measurements of a series of substituted 2-aryl derivatives 3d - 3i displayed two reversible single electron transfer steps with relatively small semiquinone formation constants between 102 and 4×103. The 4H-imidazole 3d was successfully converted into boratetraaza-pentalene 8a, which showed two well separated reduction potentials. The value of semiquinone formation constant of 8a (1.8×1015) is even higher than those reported for similar derivatives. 4H-imidazoles can also be employed for the efficient complexation of catalytically important metals as exemplified by copper complexes 11 and 12. Derivative 3m, which possesses an additional chelating pyridine substructure, formed a stable complex of structural composition Zn(3m)2 with diethyl zinc

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Tetraazafulvalenes 1 rearrange in the presence of Montmorillonite-clay to give strongly fluorescent 1,4,5,8-tetraazanaphthalenes of type 2. This observation agrees with that reported for the cross-conjugated systeme of indigo, thus indicating a dyotropic rearrangement has taken place. Inclusion of the extended p-electronsysteme of 1 should facilitate this symmetry forbidden [s 2 +s 2 ]-process. Based on these results, some reactions of heterofulvalenes and -fulvenes reported in the literature can now be explained by dyotropic rearrangements. The easy rearrangement of 1 in the presence of K10 and DMF opens the way for the synthesis of hard to obtain ring-fused pyrazines of type 2.Dyotropic rearrangements are uncatalyzed processes in which two s-bonds simultaneously undergo an intramolecular migration. 1 This process has been examined quite well in the case of organosilyl and organometallic compounds. 2 Such rearrangements have been widely employed for the stereoselective synthesis of highly substituted butyrolactones, 3 for novel transformations of silyl amides into N-cis-propenyl amides 4 as well as for tandem process from a-aminoaldehydes to aminobutyrolactones. 5In material sciences, the synthetic value of this procedure is emphasised by the direct, base-catalysed isomerisation of 1,4,5,8-tetrathianaphthalene into either tetrathiafulvalene (TTF) or BEDT-TTF. 6 Other authors have interpreted these results in the sense of an initial E1cB mechanism for this rearrangement yielding TTF and 1,4-dithiafulvenes. 7 Electrogenerated dications of tetrathioethylenes are capable to undergo an endocyclic to exocyclic (dyotropic) rearrangement. 8 In vacuo and at high temperatures (450°C), indigo can be isomerised into tetrahydro-dibenzonaphthyridine-dione 'epindolidione'. 9 Involvement of the extended p-electron-system which is capable of breaking such a symmetry-forbidden [s 2 +s 2 ]-process has been discussed in this case.The easy access of heterofulvalenes and -fulvenes together with their indigoid properties has prompted us to report a new isomerisation reaction of tetraazafulvalenes.In the course of derivatisation reactions of these heterofulvalenes, especially at temperatures above 110°C, a yellow; highly fluorescent compound was obtained. Upon isolation, mass spectroscopy indicated the same molecular composition as the starting material (1a, for example). In addition, the NMR data ( 1 H and 13 C) did not show significant differences to the starting compound. However, UV/Vis spectra revealed a clear distinction; the product (2a, for example) shows a significantly shorter wavelength absorption than compound 1a (1a: l max = 528 nm, 2a: l max = 467 nm). X-ray diffraction analysis 10 of a single crystal confirmed that 2a differs from 1a and is based on the structure of tetrakis[arylamino]-tetraazanaphthalene ( Figure 1). Figure 1 Solid state (X-ray) structure of compound 2aVariation of the reaction conditions of this rearrangement of the cross-conjugated derivatives 1 to the heteroaromatic bicycles 2 revealed that the best...

The cover picture shows the dyotropic rearrangement of 1,4,5,8‐tetraazafulvalenes into pyrazino‐[2,3‐b]pyrazines. In the case of Ar = 4‐tert‐butylphenyl, the products were immediately transformed, in the presence of oxygen, into derivatives of octaazahexacene through a cascade reaction. These highly ring‐fused compounds display a strong red fluorescence in solution and, in addition, can easily be reduced reversibly. In contact with air, the yellow fluorescent leuco compound formed quickly reoxidized, which is visible by red fluorescent streaks. Details are discussed in the article by R. Beckert et al. on p. 1237 ff.