Synthesis of enantiomerically enriched allenes by (-)-sparteine-mediated lithiation of alkynyl carbamates

The alpha -deprotonation of alkynyl carbamates 3 with the chiral base (-)-sparteine (4)/n-butyllithium, transmetalation with CITi((OPr)-Pr-/)B-3 and subsequent substitution with an aldehyde results in the formation of enantioenriched 4-hydroxyallenyl carbamates 11. Stereoselection is determined by dynamic resolution of the lithium/(-)-sparteine complexes by selective crystallization.