Asymmetric [3 + 2] Cycloaddition of 3‑Amino Oxindole-Based Azomethine Ylides and α,β-Enones with Divergent Diastereocontrol on the Spiro[pyrrolidine-oxindoles]

A general and practical
organocatalytic asymmetric 1,3-dipolar
cycloaddition of 3-amino oxindole-based azomethine ylides and α,β-enones
has been developed. This reaction delivered spiro­[pyrrolidine-2,3′-oxindole]
products in high yields with excellent regio- and enantioselectivities
(up to 99% yield, >20:1 rr, 99% ee). In addition,
an array of spiro­[dihydropyrrole-2,3′-oxindoles] were readily
accessed by oxidative dehydrogenation. Notably, the inversion of the
diastereoselectivity of the spiro­[pyrrolidine-oxindole] product could
be easily achieved through a facile oxidation–reduction process.