New Polysulfur-Nitrogen Heterocycles by Thermolysis of 1,3λ4δ2,2,4-Benzodithiadiazines in the Hydrocarbon and Fluorocarbon Series

In contrast to thermolysis of 1,3λ4δ2,2,4-benzodithiadiazine (1) and its 5,6,7,8-tetrafluoro derivative 2 in dilute (10–3M) hydrocarbon solutions, which leads to persistent 1,2,3-benzodithiazolyls in nearly quantitative yields, the thermolysis of 1 and 2 (the 6-6 bicyclic system) in concentrated (0.5 M) solutions at 150–170 °C results in complex mixtures of various polysulfur-nitrogen heterocycles, in particular differently fused 5-5-6, 5-6-7 and 5-6-6-6 polycyclic systems that were previously unknown. The products were isolated by column chromatography, and the structures of the 5-5-6 (11, 12), 5-6-7 (5, 13), and 5-6-6-6 (6, 14, 15) polycyclic systems, as well as the 6-7 (4) and 5-6 (16) bicyclic derivatives, confirmed by X-ray diffraction. The crystal packing of 6 and 11–16 is discussed with special emphasis on π-stacking interactions. The fluorescent properties of the 5-6-6-6 systems synthesized are reported. An alternative approach to the linear 5-6-6-6 system 15 based on self-condensation of an R–N=PPh3 precursor (R = 4,5,6,7-tetrafluoro-1,2,3-benzodithiazol-2-yl) is described, and the free-radical character of this new reaction is proved. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)