Highly Enantio- and Diastereoselective Generation of Two Quaternary Centers in Spirocyclopropanation of Oxindole Derivatives.
作者:Artur Noole、Natalia S. Sucman、Mikhail A. Kabeshov、Tõnis Kanger、Fliur Z. Macaev、Andrei V. Malkov
DOI:10.1002/chem.201203099
日期:2012.11.19
possible stereoisomers was obtained in the asymmetric cascade cyclopropanation of alkylidene oxindoles with ethyl 2‐chloroacetoacetate. Improved catalyst design ensured that spirocyclopropyl oxindoles featuring twoquaternarycenters were synthesized in high yield and high enantio‐ and diastereoselectivity (see scheme).
A new methodology was developed for the synthesis of enantiomerically enriched 3,3-disubstituted 3-chlorooxindoles 3 via a Michael addition of 3-chloroxindoles to nitroolefins 2, catalyzed by chiral squaramide 10. Products with adjacent quaternary–tertiary centers were isolated in excellent yields (up to 99%), high diastereoselectivities (up to 11:1), and enantiomeric purities (up to 92%). This is