Asymmetric [3 + 3] cycloaddition of cinnamaldehyde-derived N-aryl nitrones with 2-indolemethanols enabled by chiral
Ning Zou1, Yu-Zheng Wu2, Zi-Wei Shang1
1College of Chemistry and Chemical Engineering, Neijiang Normal University, Neijiang 641100, China. weicui0831@163.com.
Abstract:
We described a chiral phosphoric acid (CPA) catalyzed asymmetric [3 + 3] cycloaddition of cinnamaldehyde-derived N-aryl nitrones with 2-indolylmethanols to prepare various indole-fused 1,2-oxazines in high yields (up to 96%) with excellent enantioselectivity (>99% ee). Control experiments indicate that hydrogen bonding plays important roles in controlling the enantioselectivity of products. This strategy provides an efficient pathway to construct enantioenriched indole-fused 1,2-oxazines from N-aryl nitrones with 2-indolylmethanols.
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