The pericyclic reactions of 4,5-dimethoxycarbonyl-substituted aza-and diazafulvenium methides generated un-der microwave-induced thermolysis conditions have been described. The 7,7-dimethyl-substituted derivatives undergo al-lowed suprafacial sigmatropic [1,8]-hydrogen shifts leading to the efficient synthesis of C-vinylpyrroles and C-vinylpyrazoles. These intermediates could not be trapped in [8+2] cycloaddition in the presence of dipolarophiles. Aza-and diazafulvenium methides unsubstituted at C-1 and C-7 behave as 8 1,7-dipoles in the presence of dipolarophiles un-der microwave irradiation, leading to a range of pyrrolo and pyrazolo annulated heterocycles resulting from addition across positions 1 and 7. Aza-and diazafulvenium methide derivatives bearing only one methyl group at C-7 are inter-cepted in sigmatropic hydrogen shifts to give functionalized pyrroles and pyrazoles, respectively. In the presence of elec-tron-deficient dipolarophiles, these 7-methyl-substituted derivatives act as 1,7-dipoles in [8+2] cycloadditions, how-ever, competitive formation of the corresponding vinyl pyrroles and vinylpyrazoles is also observed.