Dyotropic Rearrangements of Tetraazafulvalenes - A New Approach to ­Aminosubstituted 1,4,5,8-Tetraazanaphthalenes

Abstract

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...