A novel synthesis of 5-perfluorophenyl 4,5-dihydro-1H-pyrazoles in THF or water

5-Perfluorophenyl 4,5-dihydro-1H-pyrazoles were synthesized from 1,3-dipolar cycloaddition reaction of perfluorobenyl 2,4,6-triisopropylbenzenesulfonylhydrazone and α,β-unsaturated carbonyl compounds or acrylonitrile in THF or water. It was worthy to note that better results were obtained when water was employed as the solvent, which was considered as an effective, economic and environmentally friendly method to synthesize these pyrazole derivatives.     

Five-membered 2,3-dioxoheterocycles: LXXXVII. [4+2]-cycloaddition of alkyl vinyl ethers and 3,4-dihydro-2H-pyran to 4,5-diaroyl-1 H-pyrrole-2,3-diones

1-Aryl-4,5-diaroyl-1H-pyrrole-2,3-diones react with alkyl vinyl ethers and 3,4-dihydro-2H-pyran affording 1,4-diaryl-7a-aroyl-6-ethoxy-7,7a-dihydropyrano[4,3-b]pyrrole-2,3(1H,6H)-diones and 1,4-diaryl-9baroyl-1,7,8,9,9a-hexahydro-5aH-pyrano[3??,2??:5,6]pyrano[4,3-b]-pyrrole-2,3-diones respectively.     

[4+2]-cycloaddition of alkyl vinyl ethers to 4,5-diaroyl-1H-pyrrole-2,3-diones

Russian Journal of Organic Chemistry -     

Thermolysis of hexasubstituted-4,5-dihydro-3H-pyrazoles: Synthesis of 1-alkoxy- and 1-acetoxy-1,2,2,3,3-pentasubstituted-cyclopropanes

A series of 5-alkoxy- and 5-acetoxy-4,4-dimethyl-3,3,5-trisubstituted-4,5-dihydro-3H-pyrazoles 2a-f (hexasubstituted pyrazolines) was synthesized by oxidation of the corresponding 3,4-dihydro-2H-pyrazoles with lead tetraacetate in the appropriate solvents. The 5-acetoxy compounds were produced when the oxidations were carried out in methylene chloride. Oxidation with lead tetraacetate in dry alcoholic solvents resulted in the formation of the 5-alkoxy derivatives as the major products. Thermolysis of the hexasubstituted-4,5-dihydro-3H-pyrazoles 2a-f in cyclohexane or as the melt at high temperature yielded the 1-alkoxy- and 1-acetoxy-1,2,2,3,3-pentasubstituted cyclopropanes 3a-f in good yields. Trace amounts of alkene products were formed in several reactions. No products attributable to cycloreversion pathways were detected. The product distributions were consistent with extrusion of nitrogen gas from 2a-f to yield the singlet 1,3-diradical, closure of which resulted in cyclopropane formation with partial retention of stereochemistry.     

Interaction of 4,5-diphenyl-2,3-dihydro-2,3-pyrroledione with ethoxycarbonylmethylenetriphenylphosphorane: synthesis and crystal structure of 4,5-diphenyl-Z-2-ethoxycarbonylmethylene-2,3-dihydro-3-pyrrolone

1-Unsubstituted 4,5-diphenyl-2,3-dihydro-2,3-pyrroledione interacts with ethoxycarbonyl-methylenetriphenylphosphorane regioselectively to give 4,5-diphenyl-Z-2-ethoxycarbonyl-methylene-2,3-dihydro-3-pyrrolone. The crystal and molecular structure of the latter was studied by X-ray analysis.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1556–1558, August, 1995.     

Reactions of fluoroalkanesulfonyl azides with cyclic vinyl ethers

The addition reactions of fluoroalkanesulfonyl azides to dihydropyran or dihydrofuran were studied. These reactions do not give the corresponding N-fluoroalkanesulfonyl azilidines but N-fluoroalkanesulfonyl-tetrahydropyranon-2-imines or N-fluoroalkanesulfonyl-tetrahydro-furano-2-imines. The reaction mechanism is discussed.     

Room temperature ICl-induced dehydration/iodination of 1-acyl-5-hydroxy-4,5-dihydro-1H-pyrazoles. a selective route to substituted 1-acyl-4-iodo-1H-pyrazoles

A number of new functionally substituted 1-acyl-5-hydroxy-4,5-dihydro-1H-pyrazoles have been prepared in moderate to excellent yields from the corresponding 2-alkyn-1-ones. The resulting dihydropyrazoles undergo dehydration and iodination in the presence of ICl and Li2CO3 at room temperature to provide 1-acyl-4-iodo-1H-pyrazoles.     

Synthesis of 3-substituted pyrazoles by oxidative dehydrogenation of 4,5-dihydro-3H-pyrazoles

Russian Journal of Organic Chemistry -     

Reactions of 2,3-dihydro-1H-cyclohepta[b]pyrazines with acyl halides

2 When3-dihydro-1H-cyclohepta[b]pyrazine ( 3 ) was treated with acetyl chloride under the Friedel-Crafts conditions, its pyrazine ring opened to afford 2-[N'-acetyl-(2-aminoethyl)amino]tropone. Reactions with propionyl and butyryl chloride also gave similarly ring-opened products. On the other hand, aromatic benzoyl chlorides reacted with compound 3 to afford N-benzoyl-substituted 2,3-dihydro-1H-cyclohepta[b]pyrazines, in addition to ring-opened compounds.     

Reaction of 3-(alken-1-yl)-4,5-dihydro-3H-pyrazoles with sodium nitrite in acetic acid

3-Vinyl-4,5-dihydro-3H-pyrazole reacted with sodium nitrite in acetic acid to give 3-vinyl-1-nitroso-4,5-dihydro-1H-pyrazole, whereas 3-isopropenyl-4,5-dihydro-3H-pyrazole under analogous conditions was unexpectedly converted into a nitro derivative, 3-(1-methyl-2-nitrovinyl)-4,5-dihydro-1H-pyrazole.     

Spiro heterocyclization of 4,5-diaroyl-2,3-dihydro-1H-pyrrole-2,3-diones with ethyl 3-amino-3-phenylprop-2-enoate

Russian Journal of Organic Chemistry -