Regiodivergence in the Cycloadditions between a Cyclic Nitrone and Carbonyl-Type Dipolarophiles

The present report details the 1,3-dipolar cycloaddition
between
a chiral cyclic nitrone (1) and different carbonyl-type
dipolarophiles, thus confirming the regiodivergence observed due to
the cyclic nature of the dipolarophile source. An ortho regioselectivity is observed in the resulting isoxazolidines when
the dipolarophile is acyclic, whereas the meta adducts
are obtained from the cyclic dipolarophiles. This evidence is supported
by both electronic calculations and X-ray diffraction.