Enantioselective Cycloadditions of 2-Alkenoylpyridine-N-oxides Catalysed by a Bis(oxazoline)/CuII Complex: Structure of the Reactive Intermediate

Diels–Alder and 1,3-dipolar cycloadditions involving (E)-3-aryl-1-(pyridin-2-yl-N-oxide)prop-2-en-1-ones as the 2p components are efficiently catalysed by bis(oxazoline)–CuII complexes. The cycloadducts are obtained in quantitative yields with up to 98% ee; absolute configurations were determined by X-ray analysis. The structure of the reactive complex, determined by X-ray analysis, is fully consistent with the stereochemical outcome of the catalysed process (approach of the diene or nitrone to the less hindered face of the coordinated pyridine-N-oxide derivative).