Cyclopropanation reactions involving a 1,4-addition to an electrophilic alkene followed by a cyclization are known as Michael initiated ring closure (MIRC) reactions. In recent years catalytic MIRC processes have attracted great interest for the asymmetric construction of cyclopropanes. With the aim of expanding our previous studies on the synthesis of densely functionalized cyclopropanes, we now report preliminary results of investigations concerning novel cyclopropanations of vinyl selenones with dinucleophilic C1 synthons. The initially formed Michael adducts, after a proton transfer, can cyclize through an intramolecular nucleophilic substitution by taking advantage of the excellent leaving group ability of the phenylselenonyl group. Encouraging results were obtained from organocatalytic reactions with unsubstituted cyanoacetates, a bifunctional cinchona alkaloid-based organocatalyst and a base additive. Cyclopropanes bearing adjacent tertiary and quaternary stereocentres were generated in good yield, high diastereoselectivity and moderate enantioselectivity.Dedicated to Professor Lorenzo Testaferri on the occasion of his retirement.
Stereoselective synthesis of cyclopropanes from vinyl selenones via a Michael-initiated ring closure reaction.
STERNATIVO, Silvia;BAGNOLI, Luana;SANTI, Claudio;MARINI, Francesca
2013
Abstract
Cyclopropanation reactions involving a 1,4-addition to an electrophilic alkene followed by a cyclization are known as Michael initiated ring closure (MIRC) reactions. In recent years catalytic MIRC processes have attracted great interest for the asymmetric construction of cyclopropanes. With the aim of expanding our previous studies on the synthesis of densely functionalized cyclopropanes, we now report preliminary results of investigations concerning novel cyclopropanations of vinyl selenones with dinucleophilic C1 synthons. The initially formed Michael adducts, after a proton transfer, can cyclize through an intramolecular nucleophilic substitution by taking advantage of the excellent leaving group ability of the phenylselenonyl group. Encouraging results were obtained from organocatalytic reactions with unsubstituted cyanoacetates, a bifunctional cinchona alkaloid-based organocatalyst and a base additive. Cyclopropanes bearing adjacent tertiary and quaternary stereocentres were generated in good yield, high diastereoselectivity and moderate enantioselectivity.Dedicated to Professor Lorenzo Testaferri on the occasion of his retirement.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
