Engaging Allene‐Derived Zwitterions in an Unprecedented Mode of Asymmetric [3+2]‐Annulation Reaction. (27th June 2016) - Sankar, Muthukumar G.
Abstract: Catalytic addition of chiral phosphine, that is, ( R )‐ or ( S )‐SITCP, to an α‐substituted allene ester generated a zwitterionic dipole. Under optimized reaction conditions, this dipole could engage isatine‐derived N ‐Boc‐ketimines in a novel mode of [3+2] annulation reaction. Pyrrolinyl spirooxindoles are thus afforded in high yields and with excellent enantioselectivities. The unprecedented annulation reaction successfully facilitated the construction of sp 3 ‐rich and highly substituted 3, 2′‐pyrrolidinyl spirooxindoles supporting many chiral centers.