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Enantioenriched carbanionic pairs generated by the asymmetric deprotonation of carbamate esters with the chiral base sbutyllithium/(−)-sparteine undergo smoothly intramolecular conjugate addition reactions to dienes and enynes in high yields.
The asymmetric deprotonation mediated by the chiral base s-butyllithium/(-)-sparteine of 4-substituted 5-hexynyl carbamates permits the synthesis of enantioenriched carbanionic pairs which undergo a regioselective 5-exo-dig ring closure with the triple bond acting as an internal electrophile. The functionalized five-membered rings are formed with complete stereoselectivity in high yields.
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