Highly enantioselective [2,3]-Wittigrearrangement of functionalized allyl benzyl ethers was accomplished using a chiral di-tert-butyl bis(oxazoline) ligand. The reaction proceeded with excellent diastereo- and enantioselectivity when no methoxy substituent was present at the ortho-position on the benzyl group. On the other hand, the enantioselectivity was drastically decreased in the presence of an
Asymmetric [2,3]-Wittig Rearrangement of Oxygenated Allyl Benzyl Ethers in the Presence of a Chiral di-<i>t</i>Bu-bis(oxazoline) Ligand: A Novel Synthetic Approach to THF Lignans
allyl benzyl ethers in the presence of a chiral di‐tBu‐bis(oxazoline) ligand. In various oxygenated benzylic ethers, the reactions proceeded with excellent diastereo‐ and enantioselectivities, although the presence of a methoxy substituent at the ortho‐position on the benzyl group drastically decreased the enantioselectivity. Conversely, o‐ethyl and o‐phenyl substituents had no significant effect on
stereoselective construction of (3R,4S,5R)- and (3R,4S,5S)-trisubstituted γ-butyrolactones 3 and 4 from (2R,3R)-2,3-dimethyl-4-pentenoic acid derivative 7, which was readily obtained via stereoselective conjugate addition of vinylmagnesium chloride to a chiral α,β-unsaturated N-acyl oxazolidinone (Evans’ auxiliary) followed by α-methylation.