Abstract
A study on the metal ion-mediated stereo- and regiocontrol of 1,3-dipolar cycloaddition reactions, which have been developed and established in Kyushu University in Kasuga, is reviewed in this account. The first success involves the generation of metal-containing 1,3-dipoles. N-Metalated azomethine ylides are generated under reversible and irreversible conditions and undergo exclusively endo-selective 1,3-dipolar cycloadditions with carbonyl-activated alkenes through the chelated transition structure. The closely related intermediates derived from bulky imine esters can be utilized for the anti-selective Michael additions. The second topic is the regio- and syn-sclective nitrone and nitrile oxide cycloadditions to allylic alcohols in the presence of magnesium ions. These reactions are magnesium ion specific. Lewis acid-mediated nitrone cycloadditions to electron-deficient alkenes have been also been discovered in Kasuga and this discovery was a starting point for the chiral Lewis acid catalyzed enantioselective nitrone cycloadditions. With powerful Lewis acid catalysts in hand, the author's group has developed highly efficient enantioselective nitrone cycloadditions and diazo cycloadditions catalyzed by the transition metal aqua complexes derived from the DBFOX/Ph ligand.
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