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- W4206365320 abstract "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." @default.
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- W4206365320 date "2000-04-01" @default.
- W4206365320 modified "2023-09-25" @default.
- W4206365320 title "Nucleophilic Substitution of 4H-Imidazoles - A Key Step in the Synthesis of Fused Imidazoles and New Chromophores" @default.
- W4206365320 doi "https://doi.org/10.1002/(sici)1099-0690(200004)2000:8<1661::aid-ejoc1661>3.3.co;2-t" @default.
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