G. V. Bozhenkov

New Synthesis and Properties of 3-Alkyl-, 3-Chloroalkyl-, 3-Perfluoroalkyl-, and 3-Aryl-1-methyl-(5-halo)pyrazoles from Chloro(bromo)vinyl Ketones and N,N-Dimethylhydrazine

A new regioselective heterocyclization was revealed in the reaction of 2-chloro- and 2,2-dichloro(bromo)vinyl ketones with N,N-dimethylhydrazine to afford 3-substituted 1-methyl(5-halo)pyrazoles. The reaction is accompanied by elimination of methyl halide and formation of up to 90% of N,N,N-trimethylhydrazinium halide as the second product.

Synthesis, structure, and characteristics of 1,2-dichlorovinyl alkyl ketones

A method of alkyl 1,2-dichlorovinyl ketones preparation from acyl halides and 1,2-dichloroethylene was developed. The configurational equilibrium and electronic structure of alkyl 1,2-dichlorovinyl ketones was investigated by IR, 1H and 13C NMR spectroscopy, by measuring dipole moments, and by quantum-chemical calculations using methods RHF and B3LYP in the basis 6–311++G (d,p). Alkyl 1,2-dichlorovinyl ketones are stable in the Z, s-cis-configuration where the olefin proton is involved into an intramolecular hydrogen bond with the oxygen of the carbonyl group. Reaction of 1,2-dichlorovinyl ketones with alkylhydrazines afforded 1-alkyl-3-alkyl-4-chloropyrazoles. The reaction of alkyl 1,2-dichlorovinyl ketones with 1,1-dimethylhydrazine involved dehydrochlorination and afforded 1,1-dimethylhydrazinium hydrochloride and a mixture of compounds with uncertain structure.

Chloro(bromo)vinyl ketones and 2,2-Dichloroacrolein in Reactions with Hydrazines

Reactions of 2,2-dichlorovinyl and 2,2-dibromovinyl ketones with alkylhydrazines afford respectively 1-R-3-alkyl(aryl)-5-chloro- or 5-bromopyrazoles in preparative yields. The dichloroacrolein forms with alkylhydrazines and dimethylhydrazine only the corresponding hydrazones. Quantum-chemical calculations were performed characterizing the structure of the obtained ketones and dichloroacrolein alkylhydrazones, of dichloroacrolein dimethylhydrazone, of 1-alkyl-5-chloropyrazolinium halides, and 1-alkyl-5-chloropyrazoles.

Structure and Properties of 2,2-Dibromovinyl Trifluoromethyl Ketone

It was established by IR spectroscopy and quantum-chemical calculations along nonempirical DFT method in B3LYP version with the basis set 6-311 G(d,p) that 2,2-dibromovinyl trifluoromethyl ketone consisted of a mixture of s-cis planar conformer and s-trans-form deviating from a plane by 13°, whereas the s-cis-form is more energetically stable than the s-trans one (ΔE -5.07 kcal mol-1). Also in 2,2-dibromovinyl methyl ketone the planar s-cis conformer is more stable. Chlorine-containing analogs, 2,2-dichlorovinyl trifluoromethyl ketone and 2,2-dichlorovinyl methyl ketone, are more stable in the planar s-trans-conformation. Charge distribution and polarization in the dibromovinyl ketones are analogous to those in dichlorovinyl ketones in agreement with the established reactivity of dibromovinyl trifluoromethyl ketone. By reaction of 2,2-dibromovinyl trifluoromethyl ketone with 2,4-dinitrophenyl-, alkylhydrazines, N,N-dimethylhydrazine, N,N-, N,O-, N,S-binucleophiles were respectively obtained hydrazone, derivatives of pyrazole, imidazole, oxazole, and 1,3-thiazine containing a trifluoromethyl group.

Synthesis and properties of 5-chloro-4-nitropyrazoles

The nitration of 5-chloropyrazoles with a mixture of 100% nitric acid and 65% oleum or a mixture of 60% nitric acid and polyphosphoric acid gave substituted 5-chloro-4-nitropyrazoles in 45–91% yield. The nitration of 3-aryl-5-halopyrazoles was accompanied by introduction of a nitro group into the aromatic ring. 4-Chloropyrazoles failed to undergo nitration under these conditions. The reaction of 5-chloro-1,3-dimethyl-4-nitropyrazole with ethyl cyanoacetate in DMSO in the presence of K2CO3 led to the formation of ethyl 2-cyano-2-(1,3-dimethyl-4-nitro-1H-pyrazol-5-yl)acetate.

Synthesis and Properties of 2,2-Dichlorovinyl Trifluoromethyl Ketone

Highly reactive 2,2-dichlorovinyl trifluoromethyl ketone was synthesized. Its reactions with N,N-and N,S-nucleophiles gave 1,3-thiazine, pyrazole, and imidazole derivatives containing a trifluoromethyl substituent.

2-chlorovinyl 1,1-dichloroethyl ketone from 2-chloropropionyl chloride and 1,2-dichloroethene

We recently found [1, 2] that chloroacetyl chloride reacts with 1,2-dichloroethylene in the presence of AlCl3 to give an unexpected product, dichloromethyl 2-chlorovinyl ketone. In contrast, aliphatic carboxylic acid chlorides and dichloroacetyl chloride were reported [3, 4] to react with 1,2-dichloroethylene under analogous conditions with formation of alkyl 1,2-dichlorovinyl ketones and 1,2-dichlorovinyl dichloromethyl ketone, respectively. In continuation of our studies on the chemistry of highly reactive 2,2-, 1,2-, and 2-chlorovinyl chloroalkyl ketones [5] we examined the reaction of 2-chloropropionyl chloride with 1,2-dichloroethylene with a view to elucidate the mechanism of reactions of α-chloroalkanoyl chlorides with 1,2-dichloroethylene. We found that 2-chloropropionyl chloride reacts with commercially available mixture of cisand trans-1,2-dichloroethylenes (a large-scale chemical product) under the conditions described in [1–4] along two concurrent pathways. The first of these unexpectedly led to the formation of 49% of previously unknown 1,1-dichloroethyl 2-chlorovinyl ketone, while the second was the known process leading to diastereoisomeric 1-chloroethyl 1,2,2-trichloroethyl ketones II and 1-chloroethyl 1,2-dichlorovinyl ketone (III) at a ratio of 69 : 13; here, compound III is formed as a result of thermal dehydrochlorination of ketone II [3, 4]. The mechanism of formation of 1,1-dichloroethyl 2-chlorovinyl ketone (I) from 1,2-dichloroethylene and 2-chloropropionyl chloride, which involves chlorotropic rearrangement, is not completely clear. The product structure suggests that the mechanism proposed by us previously for the formation of dichloromethyl 2-chlorovinyl ketone [2] from chloroacetyl chloride and 1,2-dichloroethylene is not operative here. Saturated ketone II failed to undergo transformation into 2-chlorovinyl ketone I on heating in the presence of aluminum chloride. 1,4,4-Trichloropent-1-en-3-one (I). A mixture of 18.7 g (0.14 mol) of AlCl3, 17.74 g (0.14 mol) of 2-chloropropionyl chloride, and 30 ml of 1,2-dichloroethylene was heated for 6–8 h at the boiling point. The mixture was then cooled and poured onto ice. The organic phase was separated, the aqueous phase was extracted with methylene chloride, the extracts were combined with the organic phase, dried over CaCl2, and filtered, the solvent was distilled off, and the residue was distilled under reduced pressure, a fraction ISSN 1070-4280, Russian Journal of Organic Chemistry, 2009, Vol. 45, No. 4, pp. 617–618.

Unusual reaction of chloroacetyl chloride with 1,2-dichloroethene. Synthesis and properties of 2-chlorovinyl dichloromethyl ketone

The reaction of chloroacetyl chloride with 1,2-dichloroethene in the presence of AlCl3 unexpectedly led to the formation of (E)-1,1,4-trichlorobut-3-en-2-one whose structure was proved by 1H and 13C NMR, IR, and mass spectra and independent synthesis. A probable reaction scheme was proposed, which involves transformation of initially formed 1,2,4-trichloro-3-oxobutan-2-yl cation by the action of AlCl3. The high reactivity of the vinylic halogen atom in (E)-1,1,4-trichlorobut-3-en-2-one was demonstrated by its reactions with nitrogen-centered nucleophiles (triethylamine, aniline, 3,5-dimethyl-1H-pyrazole) and sodium sulfide. These reactions involved only the C-Cl bond in the vinyl fragment and afforded (4,4-dichloro-3-oxobut-2-en-1-yl)triethylammonium chloride, 1,1-dichloro-4-phenylaminobut-3-en-2-one, 1-(4,4-dichloro-3-oxobut-2-en-1-yl)-3,5-dimethyl-1H-pyrazole, and 4,4′-thiobis(1,1-dichlorobut-3-en-2-one), respectively. The reaction of 1,1,4-trichlorobut-3-en-2-one with benzylhydrazine gave a mixture of 1,3- and 1,5-disubstituted pyrazoles.

5(4)-Chloro-1-(2,4-dinitrophenyl)pyrazoles from 2,4-Dinitrophenylhydrazones of Chlorovinyl Ketones and β,β-Dichloroacrolein

A method has been developed for obtaining 3-alkyl(phenyl)-4(5)-chloro-1-(2,4-dinitrophenyl)pyrazoles from appropriate dinitrophenylhydrazones of 1-chloro-, 1,2-, and 2,2-dichlorovinyl ketones by heating the latter in polyphosphoric acid. The structure of the pyrazoles was studied by IR and 1H NMR spectroscopy.

1-Alkylpyrazoles and 1-alkyl-5-chloropyrazoles from halovinyl ketones and 1,1-dialkylhydrazines

Regioselective heterocyclization of alkyl 2-chloro-and 2,2-dichlorovinyl ketones with 1,1-dialkyl-hydrazines to 1,3-dialkyl-1H-pyrazoles and 1,3-dialkyl-5-chloro-1H-pyrazoles involves intermediate formation of the corresponding dialkylhydrazones. Fragmentation pattern of chlorine-containing pyrazoles, 3-chloromethyl-1-methyl-1H-pyrazole and 5-chloro-1-methyl-3-propyl-1H-pyrazole, depends on the position of the halogen atom.