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 π-electron-systeme of 1 should facilitate this symmetry forbidden [σ²+σ²]-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.

Key words

heterocycles - dyotropic rearrangement - K10 clay - ­tetraazafulvalenes - pyrazinopyrazines

References

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Crystal Data for 2a.
C₃₄H₂₀F₁₂N₈·2C₄H₈O Mr = 912.79 g mol^-1, yellow prism, size 0.09 × 0.07 × 0.05 mm³, monoclinic, space group C2/c, a = 13.7887 (3), b = 25.0836 (6), c = 12.0504 (3) Å, β = 104.372 (1)°, V = 4037.44 (16) ų, T = -90 °C, Z = 4, ρ_calcd = 1.502 g cm^-3, µ (MoK_α) = 1.33 cm^-1, F(000) = 1872, 8327 reflections in h (-17/17), k (-29/32), l (-15/15), measured in the range 2.17°≤Θ≤27.48°, completeness Θ_max = 99.6%, 4627 independent reflections, R _int = 0.028, 3249 reflections with F _o>4σ(F _o), 383 parameters, 0 restraints, R1_obs = 0.047, wR2_obs = 0.115, R1_all = 0.076, wR2_all = 0.131, GOOF = 1.020, largest difference peak and hole: 0.353/-0.282 e Å^-3.
CCDC 252357 (FO1730) contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: [phone]; or [e-mail]].

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Typical Procedure for Rearranging the Tetraaza-fulvalenes.
A mixture of 1 (0.5 mmol) and 300 mg Montmorillonite in 20 mL of DMF was heated to 130 °C for 24 h. After addition of H₂O, the precipitate was filtered off and the crude product was purified by column chromatography (alumina, toluene-acetone 29:1). Compound 2a (134 mg, 35%). ¹H NMR (250 MHz, THF): δ = 8.58 (s, 4 H, NH), 8.28 (m, 8 H), 7.55 (t, J = 7.5 Hz, 4 H), 7.32 (d, J = 7.5 Hz, 4 H). ¹³C NMR (62 MHz, THF): δ = 142.0, 140.6, 134.8, 131.3, 131.3, 130.2, 127.0, 122.7, 118.4, 116.1. UV/Vis (THF): λ_max (lgε) = 329 (4.4), 440 (4.3), 467 (4.3) nm. MS (FAB in dmba): m/z = 768 (M⁺), 426, 400, 210.

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COLLECT, Data Collection Software; Nonius B.V., Netherlands, 1998.