No abstract

This lecture describes some of our studies of lithio derivatives of allyl sulfone carbanions which add α-regioselectively as well as anti diastereoselectively to Michael acceptor olefins. This can be ascribed to chelation in the Michael addition step. When the reaction leads to subsequent ring closure by using a bromoallyl sulfone, the latter acts as a methylenemethane synthon in a (3+2) Michael-initiated ring closure, affording highly functionalized cyclopentane derivatives. Such additions proceed with high stereoselectivity and with asymmetric induction leading to nonracemic substituted cyclopentanones. Additions of allyl sulfone carbanions also proceed stereoselectively to C=N systems containing a chiral auxiliary on N. These can be used in the synthesis of optically active five- and six-membered ring N-heterocycles. Furthermore, chiral groups on the allyl sulfone moiety can induce significant remote asymmetric induction, made possible by the presence of an aromatic π-system which promotes intramolecular chelation to the Li cation.

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-028Remote Asymmetric Induction in Michael Additions of Allylic Sulfones.-A new pathway of remote asymmetric induction in Michael reactions involving allylic α-phenylsulfonyl carbanions in chiral donors is reported. The transmission of asymmetry is found to depend on the presence of an aromatic nucleus bound to the chiral center of the N-substituent in the donors. The change from phenyl to naphthyl improves the diastereocontrol of the reaction, whereas with cyclohexyl equal amounts of two diastereomers are formed.