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

Abstract Primary nitro compounds have not been employed as nitrile oxide precursors in reactions with active methylene compounds because the reagents commonly used as dehydrating agents also react with these dipolarophiles. However, the Cu II ‐catalysed cycloaddition/condensation procedure has been shown to be viable with these substrates, leading directly to the expected polyfunctional isoxazoles provided nitro compounds with enhanced acidity (“activated”) were used. In the absence of added dipolarophiles, these nitro compounds underwent self‐condensation to the corresponding furoxans. However, as well as 3,4‐dibenzoylfuroxan, benzoylnitromethane predominantly gave the isomer 3‐benzoyl‐4‐nitro‐5‐phenylisoxazole, the structure of which was confirmed by crystallographic analysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)