The first successful example of the asymmetric hydrogenation of substituted a-keto ethers with Cinchona-modified Pt/Al2O3 is reported. In the absence of an additional base, kinetic resolution of the racemic starting material was observed with high diastereoselectivity and ee's up to 98% at conversions of < 50%. Addition of KOH gave a strong reaction acceleration but racemic product. Immobilization of OH- on solid ion exchangers resulted in the desired dynamic kinetic resolution, and ee's of > 80% were obtained at > 95% conversion. These effects are rationalized on the basis of a simple kinetic and structural model.
US7173141B2
申请人:——
公开号:US7173141B2
公开(公告)日:2007-02-06
Organocatalytic Enantioselective Acyloin Rearrangement of α-Hydroxy Acetals to α-Alkoxy Ketones
作者:Hua Wu、Qian Wang、Jieping Zhu
DOI:10.1002/anie.201701098
日期:2017.5.15
We report an unprecedented organocatalytic enantioselective acyloin rearrangement of α,α‐disubstituted α‐hydroxy acetals. In the presence of a catalytic amount of chiral binol‐derived N‐triflyl phosphoramide, α‐hydroxy acetals rearranged to α‐alkoxy ketones in good to high yields with high enantioselectivities. Formation of an ion pair between the in situ generated oxocarbenium ion and the chiral phosphoramide