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

Article abstract of DOI:10.3987/com-98-8443

The 4H-imidazoles (1) can be reduced after deprotonation to the trianion (4) by two consecutive single electron transfer reactions. Subsequent quenching by simple electrophiles constitutes a convenient route to the title substances of type (5). The unexpected regioselectivity towards bielectrophilic building blocks facilitates the synthesis of highly substituted heterospiranes (7) and the imidazo crown ethers (8). The trianion (4) reacted with two molecules of CS₂ at the exocyclic nitrogen atoms exclusively to afford after quenching the dithiocarbamates (10) and the cyclic thiuram sulfides (11). The new imidazole derivatives of type (5) showed only slight electron donor properties. An electrophilic attack led with preference to a quarternization of the unsubstituted ring nitrogen atom of 5, as shown by the synthesis of compound (13). A similar behaviour was observed by treatment of 5 with acetylenedicarboxylate, in which the red 1:2 adduct (14) was formed in yields up to 76 %.