ChemInform Abstract: HETEROCYCLIC COMPOUNDS FROM 3,3‐DIMERCAPTO‐1‐ARYL‐2‐PROPEN‐1‐ONES, NOTE 2, CONDENSATION WITH O‐AMINOTHIOPHENOL AND O‐AMINOPHENOL

Nardi, D; Tajana, A; Pennini, R.

doi:10.1002/chin.197526259

Cited by 1 publication

(3 citation statements)

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“…2-Phenacylbenzoxazoles can be obtained in condensation of ortho-aminophenol with 3,3-dialkoxy-, 3,3-dimercapto-1-phenylprop-2-en-1-ones [9,12] or alkyl benzoylacetates [14]. These compounds were also conveniently prepared by subtraction of one of the methyl protons in 2-methylbenzoxazole and treatment of the formed carbanion with an acylating agent such as ester of benzoic acid or benzoyl chloride [6–8,13,15–17] (Scheme 2).…”

Section: Resultsmentioning

confidence: 99%

“…aBased on integrals of the H10 signals (present paper);bSince the 1 H NMR chemical shifts for various tautomers differ insignificantly (see Table 4), contributions based on integrals of the N(CH 3 ) 2 protons are not precise;cValues in parentheses are based on integrals of the substituent protons;dLiterature data for chloroform solutions at 298 K;eOnly K and O tautomers were detected in CDCl 3 ;fThere are three different forms in CDCl 3 : [K] + [O] + [E] = 20% + 37% + 43% [12]. …”

Section: Figurementioning

confidence: 99%

“…DMSO-d 6 solution of 2-(p-nitrophenacyl)benzoxazole was also found by 1 H NMR spectroscopy to contain some amount of an enaminone form [11]. However, other authors using the same technique [12] were not able to see which of the E and O forms is present in CDCl 3 -solution of 2-phenacylbenzoxazole. Identification of the tautomers was finally cleared out by More O’Ferrall and Murray [13].…”

Section: Introductionmentioning

confidence: 99%

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Synthesis and Structural Characterization of Substituted 2-Phenacylbenzoxazoles

Skotnicka

Kolehmainen

Czeleń

et al. 2013

IJMS

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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.

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