Reduction of 4H-imidazoles - Synthesis and reactivity of 4,5-diaminoimidazoles bearing a tetraaminoethene substructure

The 4H-imidazoies (1) can be reduced after deprotonation to the trianion (4 ) by two consecutive single electron transfer reactions. Subsequent quenchi ng by simple electrophiles constitutes a convenient route to the title subs tances of type (5). The unexpected regioselectivity towards bielectrophilic building blocks facilitates the synthesis of highly substituted heterospir anes (7) and the imidazo crown ethers (8). The trianion (4) reacted with tw o molecules of CS2 at the exocyclic nitrogen atoms exclusively to afford af ter quenching the dithiocarbamates (10) and the cyclic thiuram sulfides (11 ). The new imidazole derivatives of type (5) showed only slight electron do nor properties. An electrophilic attack led with preference to a quarterniz ation of the unsubstituted ring nitrogen atom of 5, as shown by the synthes is of compound (13). A similar behaviour was observed by treatment of 5 wit h acetylenedicarboxylate, in which the red 1:2 adduct (14) was formed in yi elds up to 76 %.