ISSN:
1434-193X
Keywords:
Imidazoles
;
Nucleophilic substitutions
;
Fulvenes
;
Pseudo-azulenes
;
Heterocycles
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
---The electrophilic properties of the 4H-imidazoles 1 and their protonated derivatives 2 permit the introduction of nucleophilic building blocks, as illustrated by reactions of 1 with selected amines. Depending on the nature of the amine and the substituents R1 on the heterocycle 1, single (3) or double (4) transamination is observed. The 1H-NMR spectra of the products, as well as X-ray structure analyses of compounds 3f and 4c, confirm that the residues at the 4- and/or 5-positions of 1 are exchanged. The tautomerism between 3e-h and 3e′-h′ seems to be central to the chemistry of these mixed substituted derivatives. Using orthoesters and acetophenone dimethylacetal as cyclization partners, the imidazo[4,5-d]imidazoles 5 and the 4H-imidazo[4,5-b]pyrazines 6 are obtained, respectively. Reduction of 3e with Zn/HCl or H2S leads to the air-sensitive, strongly fluorescent leuco compounds 8. Quenching of 8 by addition of aromatic aldehydes results in a condensation reaction and, coupled with the subsequent redox disproportionation, this conversion constitutes an alternative route to imidazo[4,5-d]imidazoles of type 11. The unexpected reaction of 3e-h with Lawesson's reagent allows synthesis of the 6-azapentafulvenes 14. The relevant spectral data show 14 to be members of a new chromophoric system, in which an electron-rich five-membered ring is coupled with an electron-deficient ring.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
Permalink
