Organocatalytic syn-Selective [3 + 2]/[4 + 2] Annulations of (E)-Pyrazoloneyldiene Oxindole
Jialiang Qin1,2, Yuzhen Chen1,3, Wenhong Suo1,2
1Chinese Medicine Guangdong Laboratory/State Key Laboratory of Traditional Chinese Medicine Syndrome, The Second Affiliated Hospital of Guangzhou University of Chinese Medicine (Guangdong Provincial Hospital of Chinese Medicine), Guangzhou 510006, China.
Abstract:
H-Bonding organocatalysis enables highly syn-diastereo- and enantioselective [3 + 2]/[4 + 2] annulations of (E)-pyrazoloneyldiene oxindoles with γ/δ-hydroxyenones, furnishing the bispirotetrahydrofuran/bispirotetrahydropyran derivatives bearing vicinal quaternary centers. The reaction tolerates diverse substitution patterns to give up to 88% yield, >20:1 dr, and 99% ee. Control experiments and density functional theory were used to elucidate the role of the hydrogen-bond donor in syn-selective diastereocontrol.
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