Reaction of N-heteroaromatic cations with alkali-metal amides

N‐Heterocyclic Carbene Formation Induced Fluorescent and Colorimetric Sensing of Fluoride Using Perimidinium Derivatives

“…As illustrated in Scheme , the counterion Cl − of 1 is initially exchanged by F − (process I), followed by deprotonation to form a carbene (process II), which subsequently reacts with water to generate the colourless and fluorescent carbinol 7 a (process III), and finally the intermediate 7 a undergoes a redox disproportionation to give the fluorescent 8 a and non‐fluorescent 9 a (process IV). The insertion reaction and disproportionation that occur in processes III and IV, respectively, are possible since Pozharskii and co‐workers also observed that in the presence of both the base and water, the perimidinium salt could form a carbinol intermediate to give the products of perimidone and dihydroperimidine 16a. Formation of 10 a after adding TBAF in process V as reported by Yoon et al 10a.…”

“…The structure of 9 a was also confirmed by its X‐ray crystal structure (Scheme ). These results indicate that the carbinol 7 a was simultaneously reduced and oxidized to form two different products, and thus a redox disproportionation occurred 16a. 17 It is interesting to note that the dihydroperimidine 9 a was colourless and non‐fluorescent, while the colourless perimidone 8 a was strongly fluorescent (Figure S11 in the Supporting Information).…”

Crystal structure of (E)-2-(1-methoxyimidazol-2-yl)- 2-oxoacetaldehyde O-methyl oxime, C7H9N3O3

“…Subsequently, the product of ring-opening is assumed to react with the carbene under concomitant loss of one N-methoxy group. Asimilar fragmentation of N-methoxybenzimidazolium salts has been reported [11]. The molecules in the title crystal structure are almost planar, with one exception: the C1 methyl group is twisted out of the molecular plane by 1.25 Å. Aweak hydrogen bond is observed between the carbonyl oxygen atom O2 and the ring proton C4-H …”

“…It is known that imidazolium salts are sensitive to strong bases [11,12]. Only recently, the hydrolysis of imidazole-derived carbenes has been investigated in detail [13].N ow, the N-methoxy substitution allowed the isolation of this oximea sap roduct of the baseinduced degradation.…”

“…The mechanism of this reaction is not yet fully understood, but at entative interpretation is attempted. So far, threefacts canbesafelystated: (1) two molecules of the startingmaterial arerequired to yield one molecule of the product, (2) ar ing-opening of the first molecule must occur to produce the precursor of the new side chain, and (3) the formation of acarbene from the second molecule is most likely involved, even in water [14].The ring-opening is probably initiated by addition of ahydroxide ion to the 2-position of the imidazolium salt [11,12] or by hydrolysis of apreformed carbene [15]. Subsequently, the product of ring-opening is assumed to react with the carbene under concomitant loss of one N-methoxy group.…”