Base- and Copper-Catalysed Condensation of Primary Activated Nitro Compounds with Enolisable Compounds

Abstract. Primary nitro compounds have not been employed as nitrile oxides precursors in reactions with active methylene compounds because the reagents commonly used as dehydrating agents react with these dipolarophiles, too. However, the Cu(II) catalyzed cycloaddition-condensation procedure is shown to be practicable with these substrates leading directly to the expected polyfunctional isoxazoles, provided nitro compounds with enhanced acidity (“activated”) are used. In the absence of added dipolarophiles, these nitro compounds undergo self-condensation to the corresponding furoxans. However benzoylnitromethane, beside 3,4-dibenzoylfuroxan, gives predominantly the isomer 3-benzoyl-4-nitro-5-phenylisoxazole, whose structure has been confirmed by crystallographic analysis.