(-)-sparteine-mediated asymmetric intramolecular carbolithiation of alkenes: Synthesis of enantiopure cyclopentanes with three consecutive stereogenic centers

An asymmetric intramolecular carbolithiation reaction was developed by comb ining the (-)-sparteine-mediated enantiotopos-differentiating deprotonation and the anionic 5-exo-trig cyclization. Achiral 6-phenyl-hex-5-enyl carbam ates were efficiently cyclized furnishing regio-, diastereo- (dr > 99:1),an d enantioselectively (er >98:2) 1,2-trans-substituted cyclopentanes. The in termediate primary benzylic Lithium-carbanion pairs were - in spite of thei r configurative lability - diastereoselectively substituted by versatile el ectrophiles creating a third consecutive stereogenic center. Additionally, some 4-functionalized 6-phenylhex-5-enyl carbamates were also cyclized in h igh yield to provide enantiomericaliy pure cyclopentanes incorporating thre e adjacent stereogenic centers.