title: Enantioselective Synthesis of Quaternary Carbon Stereocenters: Addition of 3-Substituted Oxindoles to Vinyl Sulfone Catalyzed by Pentanidiums.
abstract: A pentanidium-catalyzed highly enantioselective conjugate addition of 3-alkyloxindoles to phenyl vinyl sulfone has been demonstrated. This approach allows the construction of 3,3-dialkyl-substituted oxindole frameworks with high yield and excellent enantioselectivity (up to 99%) under simple phase-transfer conditions. A variety of oxindoles bearing all-carbon quaternary stereogenic centers were obtained in the presence of 0.25 mol% pentanidium. Meanwhile, practicality was illustrated by a gram-scale asymmetric synthesis of two 3,3-dialkyl-substituted oxindoles. The resulting adduct can be smoothly transformed to the natural product analogue in a short synthetic route.
authors.affiliation: Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371 (Singapore).
authors.forename: Lili
authors.initials: L
authors.lastname: Zong
authors.affiliation: Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371 (Singapore).
authors.forename: Shubo
authors.initials: S
authors.lastname: Du
authors.affiliation: Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371 (Singapore).
authors.forename: Kek Foo
authors.initials: KF
authors.lastname: Chin
authors.affiliation: Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371 (Singapore).
authors.forename: Chao
authors.initials: C
authors.lastname: Wang
authors.affiliation: Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371 (Singapore). choonhong@ntu.edu.sg.
authors.forename: Choon-Hong
authors.initials: CH
authors.lastname: Tan
keywords: conjugate addition; organocatalysis; pentanidium; quaternary carbon stereocenter; sulfones