Chiral Squaramide-Catalyzed Michael/Alkylation Cascade Reaction for the Asymmetric Synthesis of Nitro-Spirocyclopropanes

A new diastereoselective and enantioselective cyclopropanation reaction has been developed by employing a Michael/alkylation cascade reaction between (E)-3-arylenechroman-4-one or (E)-2-arylideneindan-1-one derivatives and a bromonitroalkane with a chiral squaramide catalyst. This reaction constitutes a facile asymmetric synthesis for nitro-spirocyclopropanes that have three adjacent stereogenic centers, including one quaternary center, in moderate to good yields (up to 90%) with excellent enantio- [up to >99%ee (enantiomeric excess)] and diastereoselectivities [up to >99:1 dr (diastereomeric ratio)]. A cascade cyclopropanation reaction between (E)-3-arylenechroman-4-one or (E)-2-arylideneindan-1-one derivatives and a bromonitroalkane with a chiral squaramide catalyst has been developed. Nitro-spirocyclopropanes were obtained in moderate to good yields (up to 90%) with enantioselectivities up to >99%ee (enantiomeric excess) and diastereoselectivities up to >99:1 dr (diastereomeric ratio).