Activating Pronucleophiles with High pKa Values: Chiral Organo‐Superbases

• Published in: Angewandte Chemie International Edition Vol. 59; no. 21; pp. 8004 - 8014
• Main Authors: Wang, Yu‐Hui, Cao, Zhong‐Yan, Li, Qing‐Hua, Lin, Guo‐Qiang, Zhou, Jian, Tian, Ping
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 18.05.2020
• Edition: International ed. in English
• Subjects: acidity; Amines; Asymmetry; Atom economy; Brønsted bases; Guanidines; organocatalysis; Stereoselectivity; superbases; synthetic methods
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.201913484

Direct deprotonation represents an extremely simple, straightforward, and atom‐economic strategy to activate pronucleophiles bearing an acidic proton. However, the difficulty often arises in activating pronucleophiles with high pKa values by using conventional chiral tertiary amines. To overcome this challenge, a handful of novel chiral Brønsted superbases, including amidines, guanidines, cyclopropenimines, and iminophosphoranes, have been discovered in recent years. This minireview focuses on the application of these organo‐superbases in the catalytic asymmetric reactions of weakly acidic pronucleophiles, and highlights their comparison to the conventional tertiary amines, demonstrating the highly efficient deprotonation processes and stereoselectivity controlled conversions of the superbases. The advantage of these new superbases brings a great opportunity for developing more asymmetric transformations of weakly acidic pronucleophiles. Superbase: This Minireview focuses on chiral organo‐superbases as catalysts in asymmetric reactions of pronucleophiles with high pKa values. The performance of the organo‐superbases, compared to conventional tertiary amine bases, is highlighted. The advantage of these new superbases lies in the opportunity to develop more asymmetric transformations of weakly acidic pronucleophiles.