Reduction of 4H-Imidazoles — Synthesis and Reactivity of 4,5-Diaminoimidazoles Bearing a Tetraaminoethene Substructure

Abstract

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 %.Recently, we reported a new synthetic entry to tetraaminoethenes' via a reductionsubstitution sequence starting from oxalic amidines2 The latter may be readily reduced by alkali metak3 because of the acceptor properties of the including 1,4-diaza-1,3-diene substmcture.Subsequent reaction of the preformed dianion with various electrophiles constitutes a convenient route to highly substituted tetraaminoethenes.' Based on these experimental findings, an efficient one-pot synthesis of new macrocyclic compounds was developed.4