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AlCl3‑Catalyzed Annulations of Ynamides Involving a Torquoselective Process for the Simultaneous Control of Central and Axial Chirality

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posted on 21.09.2016, 17:22 by Yanyan Yang, Hongxu Liu, Cheng Peng, Jie Wu, Jingyi Zhang, Yan Qiao, Xiao-Na Wang, Junbiao Chang
A highly torquoselective process for simultaneous control of central and axial chirality by the annulation of terminally substituted ynamides with o-quinone methides is reported. In the presence of AlCl3, a sequence comprising a [2 + 2] cycloaddition followed by the torquoselective 4π-electrocyclic ring opening and 6π-electrocyclic ring closure leads to highly stereoselective formation of diastereoisomeric 4-amino-2H-chromenes. Terminally unsubstituted ynamides undergo AlCl3-catalyzed [4 + 2] cycloaddition with o-quinone methides providing 2-amino-4H-chromenes.