Organocatalyzed asymmetric dearomative 1,3‐dipolar cycloaddition of 2‐nitrobenzofurans and <i>N</i>‐2,2,2‐trifluoroethylisatin ketimines
Xiao‐Jian Zhou, Jian‐Qiang Zhao, Yue‐Qin Lai, Yong You, Zhen‐Hua Wang, Wei‐Cheng Yuan
Abstract
A readily available chiral cyclohexanediamine-derived bifunctional tertiary amine-squaramide catalyst is more effective for the asymmetric dearomative 1,3-dipolar cycloaddition of 2-nitrobenzofurans and N-2,2,2-trifluoroethylisatin ketimines. A range of structurally diverse spiro-fused polyheterocyclic compounds containing oxindole, pyrrolidine, and hydrobenzofuran motifs were smoothly obtained in excellent results (up to 99% yield, >20:1 dr in all cases and up to 99% ee). This method features high efficiency, mild reaction conditions, exquisite asymmetric induction, wide functional group tolerance, great potential for scale-up synthesis, and attractive product diversification.