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

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 4 pi-electrocyclic ring opening and 6 pi-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.