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Enantioselective Copper-Catalyzed Formal [4 + 2] Cycloaddition of o‑Aminophenol Derivatives with Propargylic Esters for Synthesis of Optically Active 3,4-Dihydro‑2H‑1,4-benzoxazines

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journal contribution
posted on 23.02.2016, 00:00 by Zhen-Ting Liu, Ya-Hui Wang, Fu-Lin Zhu, Xiang-Ping Hu
The first copper-catalyzed asymmetric formal [4 + 2] cycloaddition of o-aminophenol derivatives with propargylic esters as the bis-electrophilic C2 synthons for the stereoselective construction of chiral 2,3,4-trisubstituted 2H-1,4-benzoxazines bearing an exocyclic double bond has been developed. By using a structurally modified chiral ketimine P,N,N-ligand, a wide range of optically active 2H-1,4-benzoxazines were prepared in high yields and with excellent enantioselectivities (up to 97% ee).