exo-Selective Catalysts for 1,3-Dipolar Nitrone Cycloaddition

Significance

There are numerous methods for endo-selective cycloaddition reactions; however, few examples addressing exo-selectivity can be found. 1,3-Dipolar nitrone cycloadditions serve as templates for developing selective catalysts, as regio-, diastereo- and enantioselectivity must all be addressed. Using Ph-BOX ligands and Lewis acids such as Mg(II), Co(II), Ni(II) and Zn(II), selectivity can be tuned for the 1,3-dipolar cycloaddition between acryloyloxazolidinone and diphenyl nitrone. Under the optimal exo-selective conditions, >98:2 regioselectivity, 10:90 endo/exo selectivity and 99% ee _exo was obtained with trans-diphenyl-BOX ligand and Ni(ClO₄)₂ as Lewis acid.