Zn(II)-Catalyzed Isomerization/Asymmetric [3+2] Cycloaddition of 3-Butynoyl Pyrazole with Nitrones: Subsequent
Jia-Yi Liu1, Xin-Yi Chen1, Ming-Sheng Xie1
1State Key Laboratory of Antiviral Drugs, Pingyuan Laboratory, Key Laboratory of Green Chemical Media and Reactions, Ministry of Education, School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang, Henan 453007, China.
Abstract:
A highly efficient Zn(OTf)2-catalyzed tandem isomerization/[3+2] cycloaddition cascade of 3-butynoyl pyrazole with nitrones was reported using a C1-symmetric imidazolidine-pyrroloimidazolone pyridine ligand. The resulting cycloadducts readily isomerize with silica gel or Et3N to chiral 4-isoxazolines containing an endocyclic C═C bond in up to 93% yield with 99% ee. The exocyclic olefin intermediate is effectively trapped by 1,4-benzoquinone ester under Cu(II) catalysis to afford chiral spiroketal analogues with >20:1 dr.
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