Asymmetric Diels-Alder Reaction with 2-Alkenoyl Pyridine N-Oxides

Significance

Many chiral catalysts have been developed for enantioselective Diels-Alder reactions, most of them involving Cu(II) complexes. However, with pyridine alkenoyl substrates, the Cu-BOX system was restricted to cyclopenta­diene as effective diene partner. The use of the ­pyridine N-oxide increased the reactivity of the ­dienophile to allow a variety of less reactive acyclic dienes to react. It also greatly increased the selectivity, as the non-oxidized pyridine gave an endo/exo ratio of 86:14 with 19% ee for the endo-adduct 3, as opposed to the N-oxide, which gave 97.5:2.5 and 96% ee.