Synthesis of 4,5-dihydroisoxazoles from N-nitroso-4,5-dihydropyrazoles under microwave activation

Synlett

Volumn , Issue 8, 2007, Pages 1235-1238

  Stepakov, Alexander V ^a   Galkin, Ivan A ^a   Kostikov, Rafael R ^a   Starova, Galina L ^a   Starikova, Zoya A ^b   Molchanov, Alexander P ^a  

^a ST PETERSBURG STATE UNIVERSITY   (Russian Federation)

^b A N NESMEYANOV INSTITUTE OF ORGANOELEMENT COMPOUNDS   (Russian Federation)

Author keywords

Dihydroisoxazoles; Elimination; Microwave activation; N nitrosodihydropyrazoles

Indexed keywords

4,5 DIHYDROISOXAZOLE DERIVATIVE; CHLOROBENZENE; N NITROSO 4,5 DIHYDROPYRAZOLE DERIVATIVE; PYRAZOLE DERIVATIVE; UNCLASSIFIED DRUG;

ARTICLE; CHEMICAL REACTION; CHEMICAL STRUCTURE; MICROWAVE IRRADIATION; SYNTHESIS;

EID: 34249802921     PISSN: 09365214     EISSN: None     Source Type: Journal    
DOI: 10.1055/s-2007-977455     Document Type: Article

References (25)

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15. General Procedures for the Synthesis of 4,5-Dihydroisoxazoles Procedure a: N-Nitroso-4,5-dihydropyrazole 1 or 3 in PhCI-DMF (or PhCT-AcOH) was irradiated in a sealed reaction vial by the focused microwave reactor (Minotavr®) at 160 W for the time indicated in Table 1 (max. temp. 110 °C). The solvent was distilled off under reduced pressure, and the residue was purified by crystallization from methanol. Procedure b: A mixture N-nitroso-4,5-dihydropyrazole 1 or 3 (500 mg) and 2 g silica gel (Chemapol LS 5/40) was irradiated in a focused microwave reactor (Minotavr®) at 160-200 W for the time indicated in Table 1. In all reactions the compounds were isolated by adding acetone to the mixture and separating the silica gel by filtration. The solvent was removed from the filtrate under reduced pressure, and the residue was purified by crystallization from MeOH.
16. The reaction vessel was placed in the MW reactor supplied with a safety valve for release of overpressure.
17. After the set temperature of 110 °C is reached, the power regulates itself to maintain the reaction temperature.
18. Heating of the reaction mixture in PhC1 under microwave activation proceeds very slowly. The mixture of PhC1 with a more polar solvent (AcOH or DMF) was used to allow for a rapid heating process. Use of the systems PhCl-AcOH and PhCl-DMF as solvents for realization of thermolysis of N- nitrosodihydropyrazoles by conventional heating leads to a decrease in the yields of the reaction products (see Table 1).
19. 5,: C, 60.75; H, 5.10; N, 8.86. Found: C, 60.69; H, 5.14; N. 8.80.
20. The complete set of crystallographic data for ester 2a was deposited to the Cambridge Crystallographic Data Center under the deposition number CCDC 624122.
21. 5: C, 45.80; H, 3.02; N, 7.63. Found: C, 45.77; H, 2.98; N, 7.55.
22. The complete set of crystallographic data for ester 4d was deposited to the Cambridge Crystallographic Data Center under the deposition number CCDC 624121.
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