Asymmetric intramolecular carbolithiation of achiral substrates: synthesis of enantioenriched (R)-(+)-cuparene and (R)-(+)-herbertene.

Concise syntheses of the sesquiterpenes (R)-(+)-cuparene and (R)-(+)-herbertene by asymmetric cyclization of achiral olefinic alkyllithium precursors in the presence of (-)-sparteine are reported. The quaternary stereogenic center in each product is set at the final step of the synthesis by enantioselective (er = 61:39) 5-exo ring closure.