Ketene-N,N-acetals as Key Intermediates in the Formation of Tetraazapentafulvadienes

Abstract

The easily accessible bis‐amidines 2 react with adamantane‐1‐carbonyl chloride 3 to yield the 4H‐imidazole 4. If the carbonic acid chloride contains an α‐hydrogen, the reaction takes a completely different path. In this case, tetraazapentafulvadienes 11 are formed via a cascade reaction that contains two single electron transfer (SET) steps. Cyclic ketene‐N,N‐acetals 7 are postulated to be the initial intermediates, which then readily form radical cations, the presence of which could be confirmed by ESR measurements even though intramolecular trapping proved impossible due to their extreme reactivity. DFT calculations at the B3LYP/6‐311+G(d,p) level support these experimental findings. The crucial ketene‐N,N‐acetals 7 can be stabilized through steric interactions and/or the introduction of conjugated substructures, thus leading to the formation of fulvenoid structures such as 14a and 14b.

Metal-Catalyzed Cross-Coupling Reactions for the Synthesis of Functionalized 1,4,5,8-Tetraazafulvalenes

“…In contrast to the thia compound 1, only a very few 1,4,5,8tetraazafulvalenes have been described in the literature. 2 In order to remedy this deficiency, we have developed numerous new syntheses for obtaining 2 [3][4][5][6][7] as well as their vinylogous 3,5 and phenylogous 5 derivatives. In addition, various derivatizations such as alkylations, 4,5 acylations 4,5 and ring closure reactions 4,5,8 of the four secondary amine groups present in 2 have been studied.…”