2,3,6-trioxypentafulvenes .3. Reaction of 2,3,6-trioxypentafulvenes with Electrophiles

The reactivity of 2, 3, 6-trioxypentafulvenes in front of electrophiles is described. Thus the bromination of 3a,f and the nitration of 3f afforded the corresponding substitution products. The formylation of 3a,f using Smith-Bin-Manas reaction conditions initially proceeded through the C-4 substitution intermediate but it finally evolved to non fulvene structures. On the other hand, the treatment of 3a with the Vilsmeier reagent gave the 6-chloropentafulvene 13, involving the sustitution of the 6-hydroxyl group by chlorine. Finally, the treatment of 3a with p-substituted benzenediazonium chlorides afforded the hydrazones 16a-f. The H-1 NMR of the alpha-(N-15)-substituted analog of 16d showed the hydrazo tautomer as the only present in solution. When 16a-e were column chromatographed, an acetotropism took place and the rearranged products 18a-e were obtained. The structure of 18e was established by X-r-ay analysis. When the diazonium coupling reaction was carried out with the potassium salt of 3a and p-G-substituted benzenediazonium tetrafluoroborates, both the hydrazones 18 and the 6-azapentafulvenes 20 were obtained. The later products were formed by the diazonium coupling in C-5 followed by decarbonylation, in a process similar to the Japp-Klingeman reaction.