2002 imidazole derivatives

imidazole derivativesR 0190

18 - 121Ketene-N,N-acetals as Key Intermediates in the Formation ofTetraazapentafulvadienes. — Reaction of bis-amidines (I) with carboxylicacid chlorides containing α-hydrogen atoms (II) gives cyclic ketene-N,N’-acetals(IV) which are unstable and subsequently afford the corresponding dimers (III).A mechanism for this reaction cascade is proposed. Cyclic ketene-N,N’-acetalscan be stabilized in the presence of bulky substituents at the acid chlorides [cf.(VI)]. When the carboxylic acid chloride does not contain α-hydrogen atoms,the reaction with bis-amidine (Ia) provides only imidazole derivatives like(VIII). — (MUELLER, DIRK; BECKERT, RAINER; WESTON, JENNIE;GUENTHER, WOLFGANG; GOERLS, HELMAR; FRIEDRICH, MANFRED;Eur. J. Org. Chem. (2001) 23, 4551-4555; Inst. Org. Makromol. Chem.,Friedrich-Schiller-Univ., D-07743 Jena, Germany; EN)

1