Asymmetric Organocatalytic Assembly of Oxindoles Fused with Spiro-3,4-dihydropyrans with Three Contiguous Stereocenters Consisting of Vicinal Quaternary Centers

Diverse bispiro-3,4-dihydropyrans consisting of oxindole moieties with three contiguous chiral centers and vicinal quaternary stereocenters were synthesized with very good yields of up to 92% and excellent enantio-selectivity of up to 99% ee by using a proline-derived thiourea organocatalyst.