Enantioselective 1,3-dipolar cycloaddition of nitrones catalyzed by optically active cationic cobalt(III) complexes

[reaction: see text] The optically active beta-ketoiminato cationic cobalt(III) complexes were employed as efficient Lewis acid catalysts for the enantioselective 1,3-dipolar cycloaddition reaction of alpha,beta-unsaturated aldehydes with nitrones. Excellent endo selectivities and high enantioselectivities were achieved in the cycloaddition reaction of 1-cyclopentene-1-carbaldehyde and the nitrones derived from 2-halobenzaldehyde.