Organocatalytic Asymmetric Mannich Reaction of 3-Hydroxyoxindoles/3-Aminooxindoles with in Situ Generated <i>N</i>-Boc-Protected Aldimines for the Synthesis of Vicinal Oxindole–Diamines/Amino Alcohols
A highly efficient asymmetricMannichreaction of 3-monosubstituted 3-aminooxindoles/3-hydroxyoxindoles with in situ generated N-Boc-protected aldimines catalyzed by the chiral bifunctional thiourea–tertiary amine catalyst has been developed. Under mild reaction conditions, a series of structurally diverse vicinal oxindole–diamines/amino alcohols were smoothly obtained in moderate to high yields (up
conversion of 3-aminooxindoles for the diastereo- and enantioselective synthesis of homoallylic aminooxindoles has been described. The asymmetric allylicalkylation of 3-aminooxindoles with allyl carboxylates proceeded smoothly to afford a series of chiral 3-allyl-3-aminooxindoles. This work offers an alternative route to build these scaffolds. The application of this protocol is also highlighted by
copper-catalyzed intramolecular C(sp2)–N cross-coupling reaction of 3-aminooxindoles with 2-bromobenzyl bromides, a wide range of 2,3′-spirobi[indolin]-2-ones were smoothly obtained in moderate to good yields. A plausible catalytic cycle for this tandem reaction process was proposed based on the control experiments. This study represents a new perspective for the synthesis of structurally diverse spirocyclic oxindoles