Asymmetric [2,3]-wittig rearrangement of oxygenated allyl benzyl ethers in the presence of a chiral di-tBu-bis(oxazoline) ligand: a novel synthetic approach to THF lignans.
We have accomplished highly enantioselective [2,3]-Wittig rearrangements of functionalized 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 the selectivity. We found that the C2-substituent of the allylic moiety played an important role in producing high enantioselectivity. Highly enantioselective [2,3]-Wittig rearrangement in the presence of catalytic amounts of the chiral ligands is also described.
Kitamura
Maria
M
Faculty of Pharmacy, Osaka Ohtani University, 3-11-1 Nishikiori-Kita, Tondabayashi, Osaka 584-8540, Japan.
Hirokawa
Yoshimi
Y
Maezaki
Naoyoshi
N
D002384:Catalysis; D008024:Ligands; D017705:Lignans / Q000138:chemical synthesis* / Q000737:chemistry; D010080:Oxazoles / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D010647:Phenyl Ethers / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013237:Stereoisomerism
D008024:Ligands; D017705:Lignans; D010080:Oxazoles; D010647:Phenyl Ethers; D012997:Solvents; D010100:Oxygen