G. D. Krapivin

Studies of 4H-3,1-benzoxazines: 13. Bromination of 1,2-dihydro-4H-3,1-benzoxazines

Bromination of 2,4-substituted 1,2-dihydro-4H-benzoxazines with bromine in acetic acid was conducted. It was shown that either the corresponding 6,8-dibromo-1,2-hydrobenzoxazines or the products of their dehydrogenation — 6,8-dibromobenzoxazines, are primarily formed as a function of the structure of the dihydrobenzoxazine and the concentration of bromine in the reaction mixture. The structure of 6,8-dibromo-2-(5-nitrofuryl-2)-4, 4-diphenyl-1,2-dihydro-4H-3,1-benzoxazine was investigated by XSA. A stacking interaction between the nitrofuran fragment of one molecule and the condensed benzene ring of the other was detected in the crystal.

Polyfuryl(aryl)alkanes and their derivatives. 17. Synthesis of compounds of the oxazulene series

Preparative methods were developed for the synthesis of various compounds of the benzofurooxazulene series. It was established that the formation of an oxazulenium salt and a dihydrooxazulene derivative during the treatment of 3-(5-methyl-2-furyl)-2-(3-oxobutyl)benzofurans with perchloric acid results from disproportionation of the intermediate compound—an oxazulene derivative.

Polyfuryl(aryl)alkanes and their derivatives. 7. New recyclization and cyclization reactions in the 2-hydroxyaryldifurylmethane series

Reaction of 2-hydroxybenzaldehydes with α-methylfuran (sylvan) under acid-catalysis conditions was investigated. It is shown that the reaction does not stop at the step involving formation of 2-hydroxyarylfuryl-methanes but proceeds further with opening of one of furan rings and recyclization to 3-furylbenzo-furan derivatives. The latter in turn undergo transformations that lead to new heterocyclic systems — 5,6-dihydro-2,4-dimethyl-4-(5-methyl-2-furyl)-4H-benzo[b]furo[2,3-h]cyclopenta[b]furans. Data from the IR, PMR, and mass spectra, alternative synthesis, and x-ray diffraction analysis were used to confirm structures of the synthesized compounds.

Furylcyclohexenones. Conversion of 6-ethoxycarbonylcyclohexenones into 4,5-dihydroindazoles. Molecular and crystal structure of 4-phenyl-6-(5-methyl-2-furyl)-4,5-dihydroindazol-3-one

Abstract4,5-Dihydrodiazoles containing furyl substituents in positions 4 or 6 were obtained by condensation of hydrazine hydrate and 6-ethoxycarbonylcyclohexenones. XSA showed that in the crystalline state, the pyrazolone fragment of the dihydroindazole molecules has a betaine structure.

Synthesis of Conjugated Systems Based on 3-(5-Methylfur-2-yl)-2-(3-oxobutyl)benzofurans

Methods were developed for the synthesis of 3-butyl-2-(3-oxobutenyl)benzofurans and 3-(3-furylbenzofuran-2-yl)acrylic acids on the basis of 3-furyl-2-(3-oxobutyl)benzofurans.

Sterically strained conjugated systems containing a trisubstituted furan ring. Molecular structure of 5-dimethylamino-2,4-bis[2,2-dimethyl-4,6-dioxo-1,3-dioxan-5-ylidene)methyl]furan

We have synthesized sterically strained conjugated systems containing a trisubstituted furan ring. We have used X-ray diffraction to study the three-dimensional structure of 5-dimethylamino-2,4-bis[(2,2-dimethyl-4,6-dioxo-1,3-dioxan-5-ylidene)methyl]furan. We have shown that such sterically strained systems undergo nonclassical deformations with distortion of mainly bond angles, but without loss of planarity.

Furylcyclohexenones. 1. Synthesis and properties of 3- and 5-furyl-6-ethoxycarbonylcyclohexenones

Abstract3- and 5-Furylcyclohexenones were obtained by the Michael reaction of furan chalcones with acetoacetic ester. Intermediate β-cycloketols were isolated in many cases. It was found that transformations of β-cycloketols by HClO4 and TrClO4 were a function of the nature of the substituent in position5 of the alicycle. 5-Arylketols undergo dehydration, while 5-furyl derivatives split both water and the furan fragment, resulting in aromatization of the alicycle. The structure of the synthesized compounds was confirmed by the IR and PMR spectra.

Polyfuryl(aryl)alkanes and their derivatives. 13. Molecular structure of bis(5-methyl-2-furyl)(4-methoxyphenyl)methane and tris(5-methyl-2furyl)methane

Abstract4-Methoxyphenylbis(5-methyl-2-furyl)methane (I) and tris(5-methyl-2-furyl)methane (II) were investigated by x-ray crystallographic analysis. It was established that the molecules of (I) have a propeller conformation with Cs symmetry, and the furan rings are turned with the oxygen atoms towards the methine hydrogen atom. The molecule of (II) has a different conformation with C2v symmetry; one of the furan rings and the methine C-H bond lie ideally in one plane, and the other two furan rings are arranged symmetrically with the oxygen atoms in relation to this bond and incline toward eclipsing of the exocyclic C-C bond.

Synthesis and properties of 5-furyl(aryl)-Δ2-1,2,4-triazolines and -Δ2-1,3,4-thiadiazolines. Molecular and crystal structure of 2-acetylamino-5-phenyl-Δ2-1,3,4-thiadiazoline

We show that upon acylation of arylidene amidrazones of 5-nitro-2-furancarboxylic acid, 3-(5-nitro-2-furyl)-Δ2-1,2,4-triazolines or 5-(5-nitro-2-furyl)-1,2,4-triazole are formed (depending on the structure of the arylidene moiety). Δ2-1,3,4-thiadiazolines are obtained by reaction of thiosemicarbazones of aromatic and furaldehydes and furan ketones. We discuss schemes for closure of the triazolidine, triazole, and thiadiazoline rings. We describe the molecular structure of 2-acetylamino-4-acetyl-5-phenyl-Δ2-1,3,4-thiadiazoline.

Polyfuryl(Aryl)alkanes and their derivatives. 6. Stereochemistry of intramolecular rotations about the C-C+ bonds in aryl(Alkyl)difurylcarbonium ions

It was demonstrated by dynamic 1H NMR spectroscopy that for difurylmethyl and gem-difurylethyl cations conformational changes are realized through rotation of one of the furan rings, whereas in the case of aryldifurylmethyl cations conformational transformations take place as the simultaneous rotation of two aromatic rings; the correlated rotation of the two furan rings proceeds with smaller energy expenditures.