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Ketene‐ N , N ‐acetals as Key Intermediates in the Formation of Tetraazapentafulvadienes
Author(s) -
Müller Dirk,
Beckert Rainer,
Weston Jennie,
Günther Wolfgang,
Görls Helmar,
Friedrich Manfred
Publication year - 2001
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200112)2001:23<4551::aid-ejoc4551>3.0.co;2-9
Subject(s) - chemistry , ketene , reactivity (psychology) , steric effects , intramolecular force , reactive intermediate , reaction intermediate , yield (engineering) , medicinal chemistry , photochemistry , stereochemistry , organic chemistry , catalysis , medicine , materials science , alternative medicine , pathology , metallurgy
The easily accessible bis‐amidines 2 react with adamantane‐1‐carbonyl chloride 3 to yield the 4 H ‐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 .