Synthesis of Six-Membered Spirocyclic Oxindoles with Five Consecutive Stereocenters in an Asymmetric Organocatalytic One-Pot Michael/Michael/Aldol Addition Sequence

An
asymmetric organocatalytic one-pot synthesis of six-membered spirocyclic
oxindoles has been successfully developed through a relay Michael/Michael/aldol
addition reaction catalyzed by the combination of readily available
diphenylprolinol silyl ether and bifunctional quinine thiourea. The
one-pot protocol affords the highly substituted spirocyclic oxindoles
in high yields and perfect enantioselectivities. More importantly,
through judicious choice of the organocatalysts employed, this reaction
could be readily adapted to predominantly afford an alternative major
diastereomer of the product.