ASYMMETRIC [2,3]-WITTING REARRANGEMENTS IN THE PRESENCE OF SPARTEINE DERIVATIVES

Asymmetric [2,3]-Wittig rearrangements of allyl propargyl ethers in he xane were performed in the presence of s-butyllithium and (-)-alpha-is osparteine which is a C-2-symmetric chiral ligand for the alkyllithium reagent. The reactions of (Z)-or (E)-allyl 3-trimethylsilylpropargyl ethers at -78 degrees C showed good diastereoselectivities (74-100%) a nd moderate enantioselectivities (29-71%). The absolute configurations of the rearrangement products were determined by the corresponding Mo sher's esters. It was found that (-)-alpha-isosparteine induced CR) co nfiguration at the hydroxy carbon and syn stereochemistry more favorab ly. The possible transition state is discussed.