Engaging Allene-Derived Zwitterions in an Unprecedented Mode of Asymmetric [3+2]-Annulation Reaction

• Published in: Angewandte Chemie International Edition Vol. 55; no. 33; pp. 9709 - 9713
• Main Authors: Sankar, Muthukumar G., Garcia-Castro, Miguel, Golz, Christopher, Strohmann, Carsten, Kumar, Kamal
• Format: Journal Article
• Language: English
• Published: Germany Blackwell Publishing Ltd 08-08-2016; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Allene; allenes; asymmetric synthesis; Catalysis; Chemical reactions; Dipoles; Imines; Organic chemistry; Phosphine; phosphine catalysis; spirooxindoles; Zwitterions; allenes; spirooxindoles; zwitterions; asymmetric synthesis; phosphine catalysis
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201603936

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 sp3‐rich and highly substituted 3,2′‐pyrrolidinyl spirooxindoles supporting many chiral centers.
Taming a zwitterion: Chiral phosphine (R)‐ or (S)‐SITCP generates a zwitterion from α‐substituted allene ester that can engage the isatine derived ketimines in an unprecedented mode of [3+2] annulation reaction. This provides a facile asymmetric access to 3,2′‐pyrrolidinyl spirooxindoles.