Iron- and ruthenium-Lewis acid catalyzed asymmetric 1,3-dipolar cycloaddition reactions between enals and diaryl nitrones.

The highly tuned, one-point binding cationic cyclopentadienyl-iron and -ruthenium complexes 1 and 2 that incorporate chiral bidentate pentafluoroaryl-phosphinite ligands selectively coordinate and activate alpha,beta-unsaturated carbonyl compounds towards asymmetric catalytic cycloaddition reactions with diaryl nitrones. The reaction gives isoxazolidine products in good yields, with complete endo selectivity and high enantioselectivity. The products are obtained as a mixture of regioisomers in ratios varying from 96:4 to 15:85. The regioselectivity correlates directly with the electronic properties of the nitrone. This is shown by the experimental and computational data.