Reaction of N-alkylated imidazoles with 2-chloro-4quinazolinone gave mesomeric betaines, 2-(1-alkyl-1H-imidazolium-3-yl)quinazolin-4-olates, for which three tautomeric forms of N-heterocyclic carbenes (NHCs) can be formulated, in addition to an anionic NHC after deprotonation. The NHC tautomers were trapped with sulfur, selenium, triethylborane, and triphenylborane as thiones, selenones and borane adducts, respectively. We obtained two isomers of the cyclic borane adducts, diazaboroloquinazolinones with [1,5-a] and [5,1-b]-type fusion between the quinazolinone and the diazaborole rings.[a] Scheme 3. Synthesis of the target betaines; 15 N-labeled atoms are marked in blue. Numbering. The index "b" stands for "mesomeric betaine". Scheme 4. Betaine, NHC tautomers and anionic NHC of 13. 452 stants (J C-N3 ) and by 1D 15 N NMR spectra (see Table S1 and Fig. S2, Supporting Information). The long-range 1 H-15 N couplings (J HN ) with 15 N labeled and unlabeled nitrogen atoms (at natural 15 Eur.
The CÀ N coupling of 1,2,4-triazolo[1,5-a]pyrimidin-7-ones with 1-adamantanol/1-bromoadamantane leads to 1,2,4-triazolo[4,3-a]pyrimidinium-5-olates, which are represented as mesomeric betaines (MBs). The formation of MBs involves not only N-alkylation of heterocyclic framework but also the rearrangement leading to a change in the type of fusion between pyrimidine and 1,2,4-triazole fragments. The structures of the obtained products were confirmed by the Xray analysis and measurements of 13 CÀ 13 C (J CC ) coupling constants in the 1D 13 C NMR spectra of selectively 13 C-labeled samples. Treatment of the betaines with lithium bis(trimethylsilyl)amide (LiHMDS) gave anionic carbenes, which were detected by 13 C NMR spectroscopy and were trapped by reactions with phenyl isothiocyanate and sulfur. Density functional theory (DFT) and the quantum theory of atoms in molecules (QTAIM) analyses allowed for an insight into the electronic structure of the obtained betaines and N-heterocyclic carbene derivatives.[a] E.
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