ChemInform Abstract: C‐Mono‐ and ‐Dibenzoylation of 2‐Methylbenzimidazole with Benzoyl Chloride.

Kolehmainen

et al. 2013

IJMS

1H and 13C NMR spectra of eleven 2-phenacylbenzoxazoles (ketimine form) show that their CDCl3-solutions contains also (Z)-2-(benzo[d]oxazol-2-yl)-1-phenylethenols (enolimine form). Intramolecular hydrogen bonding in the latter tautomer was found to be significantly weaker than that one in respective (Z)-2-(2-hydroxy-2-phenylvinyl)pyridines. Integrals of the 1H NMR signals were used to evaluate the molar ratio of the tautomers. Strong electron-donating substituents were found to stabilize the ketimine tautomer. pKT (negative logarithm of the equilibrium constant, KT = [ketimine]/[enolimine]) was found to be linearly dependent on the Hammett substituent constant σ. The results of the MP2 ab initio calculations reveal enolimine including an intramolecular OH···N hydrogen bond to be the most stable form both with electron-donor and electron-acceptor substituents. The stability of ketimines is an intermediate of those found for enolimines and enaminones i.e., (E)-2-(benzo[d]oxazol-2(3H)-ylidene)-1-phenylethanones. 13C CPMAS NMR spectral data reveal that in the crystalline state the ketimine tautomer is predominant in p-NMe2 substituted congener. On the other hand, enolimine forms were detected there when the substituent has less electron-donating character or when it is an electron-acceptor by character.

Section: Resultsmentioning

confidence: 99%

Synthesis and Structural Characterization of Substituted 2-Phenacylbenzoxazoles

Kolehmainen

et al. 2013

IJMS

“…Non purified intermediate products 1a – 8a were always used in the subsequent synthetic step. By refluxing their morpholine solutions, 1a – 8a can be easily transformed into 2-phenacylbenzoxazoles 1b – 8b [ 14 ]. In solution, compounds 1b – 8b exist in two tautomeric forms, ketimine form ( K ) and enolimine form ( O ), through keto-enol tautomerization.…”

Section: Resultsmentioning

confidence: 99%

Substituted 2-Phenacylbenzoxazole Difluoroboranes: Synthesis, Structure and Properties

2020

Molecules

Novel fluorescent dyes such as benzoxazole-boron complexes, bearing β-ketoiminate ligands, have been synthesized and characterized with a focus on the influence of a substituent on the basic photophysical properties. 1H, 11B, 13C, 15N, and 19F nuclear magnetic resonance (NMR) spectra of substituted 2-phenacylbenzoxazole difluoroboranes have been recorded and discussed. It is worth mentioning that a high correlation coefficient was found between 15N-NMR parameters and substituent constants. The photophysical properties of these new dyes have been investigated by fluorescence and ultraviolet-visible (UV-Vis) absorption spectroscopy. The geometry optimization, vibrational spectra, and the HOMO and LUMO energies were calculated based on density functional theory with the use of the B3LYP functional and 6-311++G(d,p) basis set.

“…2-Phenacylbenzimidazoles can be obtained by a variety of methods [5][6][7][8][9][10][11][12][13]. The aforementioned syntheses are characterized by low yield; therefore, 2-phenacylbenzimidazoles were prepared by treating methylbenzimidazole 1 with benzoyl chlorides in the presence of triethylamine followed by thermal decomposition of formed (Z)-2-(1-benzoyl-1H-benzo[d]imidazol-2-yl)-1-phenylvinyl benzoates 2a-i (Scheme 2) [5,7,11]. In order to compare 2-phenacylbenzimidazoles with 2-phenacylbenzoxazoles and 1-methyl-2-phenacylbenzimidazoles studied earlier [1,2], the NMR spectra of the former compounds should be recorded from their deuterated chloroform solutions.…”

Section: Resultsmentioning

confidence: 99%

“…Light yellow solid; yield 1.22 g (87%); mp 182-183 ∘ C (lit. 176-178 [22], 179 [6], 178-178.5 [7], 178-179 ∘ C [4]); 1 H NMR (DMSO-d 6 from TMS) 4.68 (2H, s, CH 2 CO (K)), 6.10 (1H, s, CHO (O)), 7.17 (3H, m (O)), 7.42 (1H, m (O)), 7.45 7 (2H, m (O)), 7.49 (1H, m (K)), 7.57 (5H, m (K)), 7.68 (1H, m (K)), 7.86 (2H, m (O)), 8. 09 (2H, m (K)), 12.27 (1H, s, NH (O)), 12.34 (1H, s, NH (K)).…”

Section: Experimental Methodsmentioning

confidence: 99%

Tautomeric Equilibria in Solutions of 2-Phenacylbenzimidazoles

Gawinecki

2019

Heteroatom Chemistry

Detailed NMR spectral analysis of DMSO-d6 solutions of the series of substituted 2-phenacylbenzimidazoles (ketimine form, K) reveals two from three tautomeric forms. Integrals of the 1H NMR signals are used in establishing the molar ratio of tautomers. The experimental analyses are supported by quantum-chemical calculations, which satisfactorily reproduced the experimental trends. Although the reported semiempirical quantum-chemical calculations show that enaminone E, i.e., 2-(1,3-dihydro-2H-benzo[d]imidazol-2-ylidene)-1-phenylethan-1-one, was thermodynamically most stable, the results of MP2 ab initio calculations reveal the following order of stability: ketimine > enolimine > enaminone (substituents do not affect this sequence). 13C CPMAS NMR spectral data reveal that in the crystalline state the enolimine tautomer O is predominant in the p-CH3 and p-NO2 substituted congeners.