Betaine–N‐Heterocyclic Carbene Interconversions of Quinazolin‐4‐One Imidazolium Mesomeric Betaines. Sulfur, Selenium, and Borane Adduct Formation

Abstract

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.

15N Chemical Shifts and JNN-Couplings as Diagnostic Tools for Determination of the Azide–Tetrazole Equilibrium in Tetrazoloazines

“…Compound 7* was obtained by the reaction of 15 N-quinazolinone S2* (90%, 15 N) with hydrazine hydrate (see the Experimental Section and Scheme S1). The selective 15 N-labeling of quinazolinone was carried out according to a previously described protocol, using an in situ reaction of 15 N-anthranilamide S1* (90%, 15 N) with potassium ethyl xanthate (see Experimental Section and Scheme S1). The reaction of 15 N-heteroaryl hydrazine 7* with 15 N-labeled nitrous acid, generated from the 15 N-enriched sodium nitrite (98%, 15 N) and acetic acid, resulted in the formation of double 15 N-labeled azide 8**A .…”

“…The synthesis of 15 N-2-thioxo-2,3-dihydroquinazolin-4­(1 H )-one 7* is based on the interaction of 15 N-anthranilamide S1* ( 15 N, 90%) with in situ generated potassium ethylxanthate (see Scheme S1). Compound S1* was prepared according to a previously published protocol …”

“…Compound S1* was prepared according to a previously published protocol. 18 15 N 3 -Tetrazolo[1,5-b][1,2,4]triazine 6***T. CAUTION! Tetrazolyldiazonium salts are very sensitive to electrostatic discharge, friction, and impact.…”

Pyrazoles in the Intersection of Mesomeric Betaines and N-Heterocyclic Carbenes: Formation of NHC Selenium Adducts of Pyrazolium-4-aminides

“…A similar spectroscopic behavior was observed in the case of the aforementioned mesoionic compound Nitron, 21a which nevertheless undergoes typical NHC trapping reactions. Quinazolin-4-one imidazolium betaines, 40 purine-imidazolium betaines, 41 and imidazoliumphenolates, 42 which we examined earlier, behave similarly.…”

N-Heterocyclic Carbene Complexes of Nickel, Palladium, and Iridium Derived from Nitron: Synthesis, Structures, and Catalytic Properties

“…Conceptually related to Enders carbene is a derivative that features an exocyclic 4-NHPh rather than 4-Ph substituent (Figure ); however, while this NHC has not been isolated, its long-known mesoionic tautomer, (1,4-diphenyl-1,2,4-triazol-4-ium-3-yl)­phenylazanide (Nitron), − exhibits reactivity that provides access to the carbene form (Figure ). − For example, Nitron reacts with elemental sulfur to afford a thione derivative; likewise, Nitron has been used to obtain several metal complexes of the type (Nitron NHC )­ML n (M = Ru, Rh, Cu, Ag, Au) that feature the 1,2,4-triazol-5-ylidene ligand, Nitron NHC . − In view of this reactivity, Nitron has been referred to as a “crypto-NHC”. , Here, we describe further applications of Nitron as a crypto-NHC to afford 1,2,4-triazolylidene compounds of nickel, palladium, and iridium, together with their structural and catalytic properties.…”