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DOI: 10.1055/s-0029-1219115
Copper-Catalyzed Synthesis of Isoxazoles
E. Trogu, L. Cecchi, F. De Sarlo*, L. Guideri, F. Ponticelli, F. Machetti*
Università di Firenze and Università di Siena, Italy
Publication History
Publication Date:
21 January 2010 (online)
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Significance
Reported is the copper(II)-catalyzed cycloaddition/condensation of activated methylene nitro compounds 1 and 1,3-dicarbonyl compounds 2 to give polysubstituted isoxazoles 3. The best results were achieved using a combination of N-methylpiperidine (NMP) as a base in combination with Cu(OAc)2 as a catalyst in chloroform or in toluene (depending on the nitro substrates). In the absence of the dipolarophiles, the nitro compounds 1 were found to undergo self-condensation to lead to the corresponding furoxans 4. In the case of the reaction of benzoylnitromethane (1a), 3-benzoyl-4-nitro-5-phenylisoxazole 5 was also obtained due to the stronger enolic character of the benzoylnitromethane. The structure of 5 was confirmed by X-ray crystallographic structure analysis.