Tautomeric Equilibrium in Polyfluoroalkylated 5,6,7,8-Tetrahydrofurans by IR Spectroscopy

The tautomeric equilibrium in substituted 5,6,7,8-tetrahydroquinazolines was studied by IR spectroscopy. The effect of various substitutents in the pyrimidine ring and the solvent on the state of the tautomeric equilibrium was evaluated.     

Regioselective 1,4-trifluoromethylation of α,β-enones using ‘protect-in-situ’ methodology

In a convenient and efficient procedure, the nucleophilic 1,4-trifluoromethylation of several α,β-enones using (trifluoromethyl)trimethylsilane was achieved. The high regioselectivity of the reaction has been reached by blocking the carbonyl moiety of the electrophile with a bulky aluminum-centered Lewis acid.     

Synthesis of trans-2-(indol-3-yl)-3-nitrothiochroman-4-ones from 3-nitrothiochromone and indoles

1,4-Nucleophilic addition reactions of 3-nitrothiochromone with indoles gave a number of novel trans-2-(indol-3-yl)-3-nitrothiochroman-4-ones in 36–89% yields. During the reactions, the thiopyrone ring underwent no opening.     

Reactivity of 3-formyl- and 3-cyanothiochromones toward some N- and C-nucleophiles. Novel synthesis of 3-substituted 2-aminothiochromones

The reactions of 3-formylthiochromone with o-phenylenediamines, o-aminobenzenethiol, and indoles proceeded at the aldehyde group to give 3-(benzimidazol-2-yl)thiochromone, 3-(benzothiazol-2-yl)thiochromone, and 3-di(indol-3-yl)methylthiochromones, respectively. 3-Formyl- and 3-cyanothiochromones react with primary aromatic amines and phenylhydrazine to give the corresponding anils and phenylhydrazones of 3-formyl- and 2-amino-3-formylthiochromones. The reaction of 3-cyanochromones with o-phenylenediamines gave 2-amino-3-[(2-aminophenyl)iminomethyl]-4H-chromen-4-ones.     

Reaction of 2-polyfluoroacylcyclohexanones with semicarbazides

2-Polyfluoroacylcyclohexanones react with semicarbazide and thiosemicarbazide to give 2-(thio)carbamoyl-3-hydroxy-3-polyfluoroalkyl-3,3a,4,5,6,7-hexahydro-2H-indazoles, one of which was studied by X-ray diffraction. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 361–365, February, 1999.     

Reaction of 2‐(Polyfluoroacyl)cycloalkanones with Hydroxylamine

The 2‐acylcycloalkanones 1a – g and 3a – c , possessing a polyfluoroalkyl group, react with hydroxylamine regio‐ and stereoselectively to yield 4,5‐dihydroisoxazol‐5‐ols 2a – g and 4a – c , respectively, i.e., products of N‐addition to the oxo group at the cycloalkane ring (Schemes 1 and 2). The products 2 and 4 can be dehydrated under drastic conditions only (Schemes 3 and 4). The structure of one of the 4,5‐dihydroisoxazol‐5‐ols was confirmed by X‐ray crystal‐structure analysis.     

2-Trifluoromethyl-1,3-dithianylium triflate: a convenient ‘masked’ electrophilic pentafluoroethylation reagent

With 2-trifluoromethyl-1,3-dithianylium triflate for the first time the synthesis, isolation and full structural characterization of an α-perfluoroalkylcarbenium salt was achieved. The title compound can be easily obtained on a preparative scale. The thermally stable dithianylium salt in combination with fluorodesulfurization chemistry is a promising novel reagent for the electrophilic polyfluoroalkylation of organic substrates, demonstrated by the pentafluoroethylation of O-nucleophiles.     

Halogenation of Fluorinated 1,3,5‐Triketones

The behavior of linear and cyclic fluorinated 1,3,5‐triketones and their metal derivatives towards common halogenating agents was examined, and optimal reaction conditions for the straightforward synthesis of mono‐, di‐, and tetrahalogenated products were found (Schemes 1–3). An aromatization through a double HBr elimination from an α,α′‐dibrominated cyclohexanone was shown to be a promising synthetic route to 1,1′‐(2‐hydroxy‐1,3‐phenylene)bis[2,2,2‐trifluoroethanones] (= 2,6‐bis(trifluoroacetyl)phenols; Scheme 4). Additionally, the 1,3,5‐triketones prepared add readily H₂O or alcohols to produce novel bridged 2,6‐dihydroxypyran‐4‐ones (Scheme 2). The structure of the obtained compounds 6a and 7a was confirmed by X‐ray structure analysis.     

Noncyclic [10-S-5] sulfuranide dioxide salts with three S-C bonds: a new class of stable hypervalent compounds

Phenyl triflate reacts with CF3SiMe3/Q+F- (Q+ = [K(18-crown-6)]+, Me4N+) and (Me2N)3S+Me3SiF2- to afford the first noncyclic [10-S-5] sulfuranide dioxide salts, [(CF3)3SO2]-Q+, with three S-C bonds, whose molecular structure was determined by X-ray crystallography.     

3-Nitrothiochromone: simple synthesis and selected reactions

Russian Chemical Bulletin -