External chiral ligand-induced enantioselective versions of the [2,3]-Wittig sigmatropic rearrangement.
The external chiral ligand-induced enantioselective [2,3]-Wittig rearrangements of crotyl benzyl ethers and crotyl propargylic ethers are described. The most notable is that treatment of (E)-crotyl propargylic ethers with a t-butyllithium/(S;S)-bis(oxazoline) complex provides a relatively high enantioselectivity (up to 89% ee), together with a high threo-diastereoselectivity. Furthermore, examples of the "asymmetric catalytic version" of the rearrangement of crotyl benzyl ethers are presented.
Tomooka
K
K
Department of Chemical Technology, Tokyo Institute of Technology, Tokyo, Japan.
Komine
N
N
Nakai
T
T