Reaction of 1,2-hydroxylaminooximes with 1,2-diketones. Conversion of 2-acyl-1-hydroxy-3-imidazoline 3-oxides to pyrazine 1,4-dioxides

Synthesis of 2-aroyl-1-hydroxy-4,5-dimethylimidazoles by reaction of 3-hydroxyamino-2-butanone oxime with arylglyoxals*

“…The benzene ring deviates from this plane, the dihedral angle being 14.58 (5)º. There is no information in the Cambridge structural database regarding the structure of 1-hydroxyimidazoles containing an 4a-f and 5b).…”

“…Heating solutions of the nitrones 3a-c in methanol in the presence of acetic acid or nitrone 3a in acetic acid led to formation of the 1-hydroxyimidazoles 4a-c while TLC showed that the reaction mixture contained the pyrazine 1,4-dioxides 5a-c isomeric with the 1-hydroxyimidazoles 4a-c. The pyrazine 1,4-dioxide 5a was identified by TLC comparison with a known sample which is quantitatively formed by condensation of the E-isomer of 2-hydroxyamino-1-phenylethanone oxime with diacetyl [5]. As expected, carrying out the condensation of salt 1·AcOH with the arylglyoxal hydrates 2d-f by heating in methanol in the presence of acetic acid led to the 1-hydroxyimidazoles 4d-f. Typifying the 1 H NMR spectra of compounds 4a-f is the presence of a low field hydroxyl group proton signal at 13.7-14.4 ppm and for the pyrazine 1,4-dioxides 5b,c the signal for the heteroaromatic proton at 8.1-8.7 ppm (Table 1) (cf.…”

“…As expected, carrying out the condensation of salt 1·AcOH with the arylglyoxal hydrates 2d-f by heating in methanol in the presence of acetic acid led to the 1-hydroxyimidazoles 4d-f. Typifying the 1 H NMR spectra of compounds 4a-f is the presence of a low field hydroxyl group proton signal at 13.7-14.4 ppm and for the pyrazine 1,4-dioxides 5b,c the signal for the heteroaromatic proton at 8.1-8.7 ppm (Table 1) (cf. [4,5]). …”

Reaction of Z isomers of alkylaromatic 1,2-hydroxylamino oximes with 1,2-diketones

“…2 In the crystalline state, most of the condensation products (6a-f,i-o) presumably have the structure of α aroyl α methylnitrones 6A, because the IR spectra of these compounds (in KBr) show a C=O stretching band at 1650-1674 cm -1 , which is evidence for the conjugation between the aroyl and nitrone groups. 4 The position of the C=O stretching band in the IR spec trum of compound 6h (in KBr) at 1692 cm -1 is indicative of the absence of the conjugation between the aroyl and nitrone groups (tautomer B).…”

“…2 For 2 acyl 1 hydroxy 3 imidazoline 3 oxides, the tautomeric equilib rium with the open forms was not detected. 2 In the present study, we examined the reactions of Z isomers of 1,2 hydroxylamino oximes 1a-e with 1,2 diketones with the aim of preparing functional 5 hydroxy 5,6 dihydro 4H 1,2,5 oxadiazine derivatives containing the acyl group at position 6. Data on such compounds are lacking in the literature.…”